https://openjdk.java.net/ 
/*
 * Copyright (c) 2003, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang;

import java.io.File;
import java.io.FileDescriptor;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import sun.security.action.GetPropertyAction;


This class is used to create operating system processes.

Each ProcessBuilder instance manages a collection of process attributes. The start() method creates a new Process instance with those attributes. The start() method can be invoked repeatedly from the same instance to create new subprocesses with identical or related attributes. 
 The startPipeline method can be invoked to create a pipeline of new processes that send the output of each process directly to the next process. Each process has the attributes of its respective ProcessBuilder. 
Each process builder manages these process attributes:

    

  • a command, a list of strings which signifies the
external program file to be invoked and its arguments, if any.
Which string lists represent a valid operating system command is
system-dependent.  For example, it is common for each conceptual
argument to be an element in this list, but there are operating
systems where programs are expected to tokenize command line
strings themselves - on such a system a Java implementation might
require commands to contain exactly two elements.

  • an environment, which is a system-dependent mapping from
variables to values. The initial value is a copy of the environment of the current process (see System.getenv()). 
  • a working directory. The default value is the current working directory of the current process, usually the directory named by the system property user.dir. 
  • a source of standard input. By default, the subprocess reads input from a pipe. Java code can access this pipe via the output stream returned by Process.getOutputStream(). However, standard input may be redirected to another source using redirectInput. In this case, Process.getOutputStream() will return a null output stream, for which:

      

    • the write methods always throw IOException 
    • the close method does nothing 
    

  • a destination for standard output
and standard error. By default, the subprocess writes standard output and standard error to pipes. Java code can access these pipes via the input streams returned by Process.getOutputStream() and Process.getErrorStream(). However, standard output and standard error may be redirected to other destinations using redirectOutput and redirectError. In this case, Process.getInputStream() and/or Process.getErrorStream() will return a null input
stream, for which:

      

    • the read methods always return -1 
    • the available method always returns 0 
    • the close method does nothing 
    

  • a redirectErrorStream property. Initially, this property is false, meaning that the standard output and error output of a subprocess are sent to two separate streams, which can be accessed using the Process.getInputStream() and Process.getErrorStream() methods. 
    If the value is set to true, then: 
      

    • standard error is merged with the standard output and always sent
to the same destination (this makes it easier to correlate error
messages with the corresponding output)

    • the common destination of standard error and standard output can be redirected using redirectOutput 
    • any redirection set by the redirectError method is ignored when creating a subprocess 
    • the stream returned from Process.getErrorStream() will always be a null input stream

    



Modifying a process builder's attributes will affect processes subsequently started by that object's start() method, but will never affect previously started processes or the Java process itself. 
Most error checking is performed by the start() method. It is possible to modify the state of an object so that start() will fail. For example, setting the command attribute to an empty list will not throw an exception unless start() is invoked. 
Note that this class is not synchronized. If multiple threads access a ProcessBuilder instance concurrently, and at least one of the threads modifies one of the attributes structurally, it must be synchronized externally.

Starting a new process which uses the default working directory
and environment is easy:

 
Process p = new ProcessBuilder("myCommand", "myArg").start();



Here is an example that starts a process with a modified working
directory and environment, and redirects standard output and error
to be appended to a log file:

 
ProcessBuilder pb =
  new ProcessBuilder("myCommand", "myArg1", "myArg2");
Map<String, String> env = pb.environment();
env.put("VAR1", "myValue");
env.remove("OTHERVAR");
env.put("VAR2", env.get("VAR1") + "suffix");
pb.directory(new File("myDir"));
File log = new File("log");
pb.redirectErrorStream(true);
pb.redirectOutput(Redirect.appendTo(log));
Process p = pb.start();
assert pb.redirectInput() == Redirect.PIPE;
assert pb.redirectOutput().file() == log;
assert p.getInputStream().read() == -1;



To start a process with an explicit set of environment variables, first call Map.clear() before adding environment variables. 
 Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown. 
Author:Martin Buchholz
Since:1.5
/**
 * This class is used to create operating system processes.
 *
 * <p>Each {@code ProcessBuilder} instance manages a collection
 * of process attributes.  The {@link #start()} method creates a new
 * {@link Process} instance with those attributes.  The {@link
 * #start()} method can be invoked repeatedly from the same instance
 * to create new subprocesses with identical or related attributes.
 * <p>
 * The {@link #startPipeline startPipeline} method can be invoked to create
 * a pipeline of new processes that send the output of each process
 * directly to the next process.  Each process has the attributes of
 * its respective ProcessBuilder.
 *
 * <p>Each process builder manages these process attributes:
 *
 * <ul>
 *
 * <li>a <i>command</i>, a list of strings which signifies the
 * external program file to be invoked and its arguments, if any.
 * Which string lists represent a valid operating system command is
 * system-dependent.  For example, it is common for each conceptual
 * argument to be an element in this list, but there are operating
 * systems where programs are expected to tokenize command line
 * strings themselves - on such a system a Java implementation might
 * require commands to contain exactly two elements.
 *
 * <li>an <i>environment</i>, which is a system-dependent mapping from
 * <i>variables</i> to <i>values</i>.  The initial value is a copy of
 * the environment of the current process (see {@link System#getenv()}).
 *
 * <li>a <i>working directory</i>.  The default value is the current
 * working directory of the current process, usually the directory
 * named by the system property {@code user.dir}.
 *
 * <li><a id="redirect-input">a source of <i>standard input</i></a>.
 * By default, the subprocess reads input from a pipe.  Java code
 * can access this pipe via the output stream returned by
 * {@link Process#getOutputStream()}.  However, standard input may
 * be redirected to another source using
 * {@link #redirectInput(Redirect) redirectInput}.
 * In this case, {@link Process#getOutputStream()} will return a
 * <i>null output stream</i>, for which:
 *
 * <ul>
 * <li>the {@link OutputStream#write(int) write} methods always
 * throw {@code IOException}
 * <li>the {@link OutputStream#close() close} method does nothing
 * </ul>
 *
 * <li><a id="redirect-output">a destination for <i>standard output</i>
 * and <i>standard error</i></a>.  By default, the subprocess writes standard
 * output and standard error to pipes.  Java code can access these pipes
 * via the input streams returned by {@link Process#getOutputStream()} and
 * {@link Process#getErrorStream()}.  However, standard output and
 * standard error may be redirected to other destinations using
 * {@link #redirectOutput(Redirect) redirectOutput} and
 * {@link #redirectError(Redirect) redirectError}.
 * In this case, {@link Process#getInputStream()} and/or
 * {@link Process#getErrorStream()} will return a <i>null input
 * stream</i>, for which:
 *
 * <ul>
 * <li>the {@link InputStream#read() read} methods always return
 * {@code -1}
 * <li>the {@link InputStream#available() available} method always returns
 * {@code 0}
 * <li>the {@link InputStream#close() close} method does nothing
 * </ul>
 *
 * <li>a <i>redirectErrorStream</i> property.  Initially, this property
 * is {@code false}, meaning that the standard output and error
 * output of a subprocess are sent to two separate streams, which can
 * be accessed using the {@link Process#getInputStream()} and {@link
 * Process#getErrorStream()} methods.
 *
 * <p>If the value is set to {@code true}, then:
 *
 * <ul>
 * <li>standard error is merged with the standard output and always sent
 * to the same destination (this makes it easier to correlate error
 * messages with the corresponding output)
 * <li>the common destination of standard error and standard output can be
 * redirected using
 * {@link #redirectOutput(Redirect) redirectOutput}
 * <li>any redirection set by the
 * {@link #redirectError(Redirect) redirectError}
 * method is ignored when creating a subprocess
 * <li>the stream returned from {@link Process#getErrorStream()} will
 * always be a <a href="#redirect-output">null input stream</a>
 * </ul>
 *
 * </ul>
 *
 * <p>Modifying a process builder's attributes will affect processes
 * subsequently started by that object's {@link #start()} method, but
 * will never affect previously started processes or the Java process
 * itself.
 *
 * <p>Most error checking is performed by the {@link #start()} method.
 * It is possible to modify the state of an object so that {@link
 * #start()} will fail.  For example, setting the command attribute to
 * an empty list will not throw an exception unless {@link #start()}
 * is invoked.
 *
 * <p><strong>Note that this class is not synchronized.</strong>
 * If multiple threads access a {@code ProcessBuilder} instance
 * concurrently, and at least one of the threads modifies one of the
 * attributes structurally, it <i>must</i> be synchronized externally.
 *
 * <p>Starting a new process which uses the default working directory
 * and environment is easy:
 *
 * <pre> {@code
 * Process p = new ProcessBuilder("myCommand", "myArg").start();
 * }</pre>
 *
 * <p>Here is an example that starts a process with a modified working
 * directory and environment, and redirects standard output and error
 * to be appended to a log file:
 *
 * <pre> {@code
 * ProcessBuilder pb =
 *   new ProcessBuilder("myCommand", "myArg1", "myArg2");
 * Map<String, String> env = pb.environment();
 * env.put("VAR1", "myValue");
 * env.remove("OTHERVAR");
 * env.put("VAR2", env.get("VAR1") + "suffix");
 * pb.directory(new File("myDir"));
 * File log = new File("log");
 * pb.redirectErrorStream(true);
 * pb.redirectOutput(Redirect.appendTo(log));
 * Process p = pb.start();
 * assert pb.redirectInput() == Redirect.PIPE;
 * assert pb.redirectOutput().file() == log;
 * assert p.getInputStream().read() == -1;
 * }</pre>
 *
 * <p>To start a process with an explicit set of environment
 * variables, first call {@link java.util.Map#clear() Map.clear()}
 * before adding environment variables.
 *
 * <p>
 * Unless otherwise noted, passing a {@code null} argument to a constructor
 * or method in this class will cause a {@link NullPointerException} to be
 * thrown.
 *
 * @author Martin Buchholz
 * @since 1.5
 */

public final class ProcessBuilder
{
    private List<String> command;
    private File directory;
    private Map<String,String> environment;
    private boolean redirectErrorStream;
    private Redirect[] redirects;

    
Constructs a process builder with the specified operating
system program and arguments.  This constructor does not make a copy of the command list. Subsequent updates to the list will be reflected in the state of the process builder. It is not checked whether command corresponds to a valid operating system command. 
Params:
  • command – the list containing the program and its arguments
/**
     * Constructs a process builder with the specified operating
     * system program and arguments.  This constructor does <i>not</i>
     * make a copy of the {@code command} list.  Subsequent
     * updates to the list will be reflected in the state of the
     * process builder.  It is not checked whether
     * {@code command} corresponds to a valid operating system
     * command.
     *
     * @param  command the list containing the program and its arguments
     */
    public ProcessBuilder(List<String> command) {
        if (command == null)
            throw new NullPointerException();
        this.command = command;
    }

    
Constructs a process builder with the specified operating system program and arguments. This is a convenience constructor that sets the process builder's command to a string list containing the same strings as the command array, in the same order. It is not checked whether command corresponds to a valid operating system command. 
Params:
  • command – a string array containing the program and its arguments
/**
     * Constructs a process builder with the specified operating
     * system program and arguments.  This is a convenience
     * constructor that sets the process builder's command to a string
     * list containing the same strings as the {@code command}
     * array, in the same order.  It is not checked whether
     * {@code command} corresponds to a valid operating system
     * command.
     *
     * @param command a string array containing the program and its arguments
     */
    public ProcessBuilder(String... command) {
        this.command = new ArrayList<>(command.length);
        for (String arg : command)
            this.command.add(arg);
    }

    
Sets this process builder's operating system program and
arguments.  This method does not make a copy of the command list. Subsequent updates to the list will be reflected in the state of the process builder. It is not checked whether command corresponds to a valid operating system command. 
Params:
  • command – the list containing the program and its arguments
Returns:this process builder
/**
     * Sets this process builder's operating system program and
     * arguments.  This method does <i>not</i> make a copy of the
     * {@code command} list.  Subsequent updates to the list will
     * be reflected in the state of the process builder.  It is not
     * checked whether {@code command} corresponds to a valid
     * operating system command.
     *
     * @param  command the list containing the program and its arguments
     * @return this process builder
     */
    public ProcessBuilder command(List<String> command) {
        if (command == null)
            throw new NullPointerException();
        this.command = command;
        return this;
    }

    
Sets this process builder's operating system program and arguments. This is a convenience method that sets the command to a string list containing the same strings as the command array, in the same order. It is not checked whether command corresponds to a valid operating system command. 
Params:
  • command – a string array containing the program and its arguments
Returns:this process builder
/**
     * Sets this process builder's operating system program and
     * arguments.  This is a convenience method that sets the command
     * to a string list containing the same strings as the
     * {@code command} array, in the same order.  It is not
     * checked whether {@code command} corresponds to a valid
     * operating system command.
     *
     * @param  command a string array containing the program and its arguments
     * @return this process builder
     */
    public ProcessBuilder command(String... command) {
        this.command = new ArrayList<>(command.length);
        for (String arg : command)
            this.command.add(arg);
        return this;
    }

    
Returns this process builder's operating system program and
arguments.  The returned list is not a copy.  Subsequent
updates to the list will be reflected in the state of this
process builder.

Returns:this process builder's program and its arguments
/**
     * Returns this process builder's operating system program and
     * arguments.  The returned list is <i>not</i> a copy.  Subsequent
     * updates to the list will be reflected in the state of this
     * process builder.
     *
     * @return this process builder's program and its arguments
     */
    public List<String> command() {
        return command;
    }

    
Returns a string map view of this process builder's environment. Whenever a process builder is created, the environment is initialized to a copy of the current process environment (see System.getenv()). Subprocesses subsequently started by this object's start() method will use this map as their environment. 
The returned object may be modified using ordinary Map operations. These modifications will be visible to subprocesses started via the start() method. Two ProcessBuilder instances always contain independent process environments, so changes to the returned map will never be reflected in any other ProcessBuilder instance or the values returned by System.getenv. 
If the system does not support environment variables, an
empty map is returned.

The returned map does not permit null keys or values. Attempting to insert or query the presence of a null key or value will throw a NullPointerException. Attempting to query the presence of a key or value which is not of type String will throw a ClassCastException. 
The behavior of the returned map is system-dependent. A system may not allow modifications to environment variables or may forbid certain variable names or values. For this reason, attempts to modify the map may fail with UnsupportedOperationException or IllegalArgumentException if the modification is not permitted by the operating system. 
Since the external format of environment variable names and
values is system-dependent, there may not be a one-to-one
mapping between them and Java's Unicode strings.  Nevertheless,
the map is implemented in such a way that environment variables
which are not modified by Java code will have an unmodified
native representation in the subprocess.

The returned map and its collection views may not obey the general contract of the Object.equals and Object.hashCode methods. 
The returned map is typically case-sensitive on all platforms.

If a security manager exists, its checkPermission method is called with a RuntimePermission("getenv.*") permission. This may result in a SecurityException being thrown. 
When passing information to a Java subprocess,
system properties
are generally preferred over environment variables.

Throws:
See Also:
Returns:this process builder's environment
/**
     * Returns a string map view of this process builder's environment.
     *
     * Whenever a process builder is created, the environment is
     * initialized to a copy of the current process environment (see
     * {@link System#getenv()}).  Subprocesses subsequently started by
     * this object's {@link #start()} method will use this map as
     * their environment.
     *
     * <p>The returned object may be modified using ordinary {@link
     * java.util.Map Map} operations.  These modifications will be
     * visible to subprocesses started via the {@link #start()}
     * method.  Two {@code ProcessBuilder} instances always
     * contain independent process environments, so changes to the
     * returned map will never be reflected in any other
     * {@code ProcessBuilder} instance or the values returned by
     * {@link System#getenv System.getenv}.
     *
     * <p>If the system does not support environment variables, an
     * empty map is returned.
     *
     * <p>The returned map does not permit null keys or values.
     * Attempting to insert or query the presence of a null key or
     * value will throw a {@link NullPointerException}.
     * Attempting to query the presence of a key or value which is not
     * of type {@link String} will throw a {@link ClassCastException}.
     *
     * <p>The behavior of the returned map is system-dependent.  A
     * system may not allow modifications to environment variables or
     * may forbid certain variable names or values.  For this reason,
     * attempts to modify the map may fail with
     * {@link UnsupportedOperationException} or
     * {@link IllegalArgumentException}
     * if the modification is not permitted by the operating system.
     *
     * <p>Since the external format of environment variable names and
     * values is system-dependent, there may not be a one-to-one
     * mapping between them and Java's Unicode strings.  Nevertheless,
     * the map is implemented in such a way that environment variables
     * which are not modified by Java code will have an unmodified
     * native representation in the subprocess.
     *
     * <p>The returned map and its collection views may not obey the
     * general contract of the {@link Object#equals} and
     * {@link Object#hashCode} methods.
     *
     * <p>The returned map is typically case-sensitive on all platforms.
     *
     * <p>If a security manager exists, its
     * {@link SecurityManager#checkPermission checkPermission} method
     * is called with a
     * {@link RuntimePermission}{@code ("getenv.*")} permission.
     * This may result in a {@link SecurityException} being thrown.
     *
     * <p>When passing information to a Java subprocess,
     * <a href=System.html#EnvironmentVSSystemProperties>system properties</a>
     * are generally preferred over environment variables.
     *
     * @return this process builder's environment
     *
     * @throws SecurityException
     *         if a security manager exists and its
     *         {@link SecurityManager#checkPermission checkPermission}
     *         method doesn't allow access to the process environment
     *
     * @see    Runtime#exec(String[],String[],java.io.File)
     * @see    System#getenv()
     */
    public Map<String,String> environment() {
        SecurityManager security = System.getSecurityManager();
        if (security != null)
            security.checkPermission(new RuntimePermission("getenv.*"));

        if (environment == null)
            environment = ProcessEnvironment.environment();

        assert environment != null;

        return environment;
    }

    // Only for use by Runtime.exec(...envp...)
    ProcessBuilder environment(String[] envp) {
        assert environment == null;
        if (envp != null) {
            environment = ProcessEnvironment.emptyEnvironment(envp.length);
            assert environment != null;

            for (String envstring : envp) {
                // Before 1.5, we blindly passed invalid envstrings
                // to the child process.
                // We would like to throw an exception, but do not,
                // for compatibility with old broken code.

                // Silently discard any trailing junk.
                if (envstring.indexOf((int) '\u0000') != -1)
                    envstring = envstring.replaceFirst("\u0000.*", "");

                int eqlsign =
                    envstring.indexOf('=', ProcessEnvironment.MIN_NAME_LENGTH);
                // Silently ignore envstrings lacking the required `='.
                if (eqlsign != -1)
                    environment.put(envstring.substring(0,eqlsign),
                                    envstring.substring(eqlsign+1));
            }
        }
        return this;
    }

    
Returns this process builder's working directory. Subprocesses subsequently started by this object's start() method will use this as their working directory. The returned value may be null -- this means to use the working directory of the current Java process, usually the directory named by the system property user.dir, as the working directory of the child process. 
Returns:this process builder's working directory
/**
     * Returns this process builder's working directory.
     *
     * Subprocesses subsequently started by this object's {@link
     * #start()} method will use this as their working directory.
     * The returned value may be {@code null} -- this means to use
     * the working directory of the current Java process, usually the
     * directory named by the system property {@code user.dir},
     * as the working directory of the child process.
     *
     * @return this process builder's working directory
     */
    public File directory() {
        return directory;
    }

    
Sets this process builder's working directory. Subprocesses subsequently started by this object's start() method will use this as their working directory. The argument may be null -- this means to use the working directory of the current Java process, usually the directory named by the system property user.dir, as the working directory of the child process. 
Params:
  • directory – the new working directory
Returns:this process builder
/**
     * Sets this process builder's working directory.
     *
     * Subprocesses subsequently started by this object's {@link
     * #start()} method will use this as their working directory.
     * The argument may be {@code null} -- this means to use the
     * working directory of the current Java process, usually the
     * directory named by the system property {@code user.dir},
     * as the working directory of the child process.
     *
     * @param  directory the new working directory
     * @return this process builder
     */
    public ProcessBuilder directory(File directory) {
        this.directory = directory;
        return this;
    }

    // ---------------- I/O Redirection ----------------

    
Implements a null input stream.

/**
     * Implements a <a href="#redirect-output">null input stream</a>.
     */
    static class NullInputStream extends InputStream {
        static final NullInputStream INSTANCE = new NullInputStream();
        private NullInputStream() {}
        public int read()      { return -1; }
        public int available() { return 0; }
    }

    
Implements a null output stream.

/**
     * Implements a <a href="#redirect-input">null output stream</a>.
     */
    static class NullOutputStream extends OutputStream {
        static final NullOutputStream INSTANCE = new NullOutputStream();
        private NullOutputStream() {}
        public void write(int b) throws IOException {
            throw new IOException("Stream closed");
        }
    }

    
Represents a source of subprocess input or a destination of subprocess output. Each Redirect instance is one of the following: 

Each of the above categories has an associated unique Type. 
Since:1.7
/**
     * Represents a source of subprocess input or a destination of
     * subprocess output.
     *
     * Each {@code Redirect} instance is one of the following:
     *
     * <ul>
     * <li>the special value {@link #PIPE Redirect.PIPE}
     * <li>the special value {@link #INHERIT Redirect.INHERIT}
     * <li>the special value {@link #DISCARD Redirect.DISCARD}
     * <li>a redirection to read from a file, created by an invocation of
     *     {@link Redirect#from Redirect.from(File)}
     * <li>a redirection to write to a file,  created by an invocation of
     *     {@link Redirect#to Redirect.to(File)}
     * <li>a redirection to append to a file, created by an invocation of
     *     {@link Redirect#appendTo Redirect.appendTo(File)}
     * </ul>
     *
     * <p>Each of the above categories has an associated unique
     * {@link Type Type}.
     *
     * @since 1.7
     */
    public abstract static class Redirect {
        private static final File NULL_FILE = new File(
                (GetPropertyAction.privilegedGetProperty("os.name")
                        .startsWith("Windows") ? "NUL" : "/dev/null")
        );

        
The type of a Redirect. 
/**
         * The type of a {@link Redirect}.
         */
        public enum Type {
            
The type of Redirect.PIPE. 
/**
             * The type of {@link Redirect#PIPE Redirect.PIPE}.
             */
            PIPE,

            
The type of Redirect.INHERIT. 
/**
             * The type of {@link Redirect#INHERIT Redirect.INHERIT}.
             */
            INHERIT,

            
The type of redirects returned from Redirect.from(File). 
/**
             * The type of redirects returned from
             * {@link Redirect#from Redirect.from(File)}.
             */
            READ,

            
The type of redirects returned from Redirect.to(File). 
/**
             * The type of redirects returned from
             * {@link Redirect#to Redirect.to(File)}.
             */
            WRITE,

            
The type of redirects returned from Redirect.appendTo(File). 
/**
             * The type of redirects returned from
             * {@link Redirect#appendTo Redirect.appendTo(File)}.
             */
            APPEND
        };

        
Returns the type of this Redirect. 
Returns:the type of this Redirect
/**
         * Returns the type of this {@code Redirect}.
         * @return the type of this {@code Redirect}
         */
        public abstract Type type();

        
Indicates that subprocess I/O will be connected to the
current Java process over a pipe.
This is the default handling of subprocess standard I/O.

It will always be true that
 
 
Redirect.PIPE.file() == null &&
Redirect.PIPE.type() == Redirect.Type.PIPE



/**
         * Indicates that subprocess I/O will be connected to the
         * current Java process over a pipe.
         *
         * This is the default handling of subprocess standard I/O.
         *
         * <p>It will always be true that
         *  <pre> {@code
         * Redirect.PIPE.file() == null &&
         * Redirect.PIPE.type() == Redirect.Type.PIPE
         * }</pre>
         */
        public static final Redirect PIPE = new Redirect() {
                public Type type() { return Type.PIPE; }
                public String toString() { return type().toString(); }};

        
Indicates that subprocess I/O source or destination will be the
same as those of the current process.  This is the normal
behavior of most operating system command interpreters (shells).

It will always be true that
 
 
Redirect.INHERIT.file() == null &&
Redirect.INHERIT.type() == Redirect.Type.INHERIT



/**
         * Indicates that subprocess I/O source or destination will be the
         * same as those of the current process.  This is the normal
         * behavior of most operating system command interpreters (shells).
         *
         * <p>It will always be true that
         *  <pre> {@code
         * Redirect.INHERIT.file() == null &&
         * Redirect.INHERIT.type() == Redirect.Type.INHERIT
         * }</pre>
         */
        public static final Redirect INHERIT = new Redirect() {
                public Type type() { return Type.INHERIT; }
                public String toString() { return type().toString(); }};


        
Indicates that subprocess output will be discarded.
A typical implementation discards the output by writing to
an operating system specific "null file".

It will always be true that

 
Redirect.DISCARD.file() is the filename appropriate for the operating system
and may be null &&
Redirect.DISCARD.type() == Redirect.Type.WRITE



Since:9
/**
         * Indicates that subprocess output will be discarded.
         * A typical implementation discards the output by writing to
         * an operating system specific "null file".
         *
         * <p>It will always be true that
         * <pre> {@code
         * Redirect.DISCARD.file() is the filename appropriate for the operating system
         * and may be null &&
         * Redirect.DISCARD.type() == Redirect.Type.WRITE
         * }</pre>
         * @since 9
         */
        public static final Redirect DISCARD = new Redirect() {
                public Type type() { return Type.WRITE; }
                public String toString() { return type().toString(); }
                public File file() { return NULL_FILE; }
                boolean append() { return false; }
        };

        
Returns the File source or destination associated with this redirect, or null if there is no such file. 
Returns:the file associated with this redirect, or null if there is no such file
/**
         * Returns the {@link File} source or destination associated
         * with this redirect, or {@code null} if there is no such file.
         *
         * @return the file associated with this redirect,
         *         or {@code null} if there is no such file
         */
        public File file() { return null; }

        
When redirected to a destination file, indicates if the output
is to be written to the end of the file.

/**
         * When redirected to a destination file, indicates if the output
         * is to be written to the end of the file.
         */
        boolean append() {
            throw new UnsupportedOperationException();
        }

        
Returns a redirect to read from the specified file.

It will always be true that
 
 
Redirect.from(file).file() == file &&
Redirect.from(file).type() == Redirect.Type.READ



Params:
  • file – The File for the Redirect.
Returns:a redirect to read from the specified file
/**
         * Returns a redirect to read from the specified file.
         *
         * <p>It will always be true that
         *  <pre> {@code
         * Redirect.from(file).file() == file &&
         * Redirect.from(file).type() == Redirect.Type.READ
         * }</pre>
         *
         * @param file The {@code File} for the {@code Redirect}.
         * @return a redirect to read from the specified file
         */
        public static Redirect from(final File file) {
            if (file == null)
                throw new NullPointerException();
            return new Redirect() {
                    public Type type() { return Type.READ; }
                    public File file() { return file; }
                    public String toString() {
                        return "redirect to read from file \"" + file + "\"";
                    }
                };
        }

        
Returns a redirect to write to the specified file.
If the specified file exists when the subprocess is started,
its previous contents will be discarded.

It will always be true that
 
 
Redirect.to(file).file() == file &&
Redirect.to(file).type() == Redirect.Type.WRITE



Params:
  • file – The File for the Redirect.
Returns:a redirect to write to the specified file
/**
         * Returns a redirect to write to the specified file.
         * If the specified file exists when the subprocess is started,
         * its previous contents will be discarded.
         *
         * <p>It will always be true that
         *  <pre> {@code
         * Redirect.to(file).file() == file &&
         * Redirect.to(file).type() == Redirect.Type.WRITE
         * }</pre>
         *
         * @param file The {@code File} for the {@code Redirect}.
         * @return a redirect to write to the specified file
         */
        public static Redirect to(final File file) {
            if (file == null)
                throw new NullPointerException();
            return new Redirect() {
                    public Type type() { return Type.WRITE; }
                    public File file() { return file; }
                    public String toString() {
                        return "redirect to write to file \"" + file + "\"";
                    }
                    boolean append() { return false; }
                };
        }

        
Returns a redirect to append to the specified file.
Each write operation first advances the position to the
end of the file and then writes the requested data.
Whether the advancement of the position and the writing
of the data are done in a single atomic operation is
system-dependent and therefore unspecified.

It will always be true that
 
 
Redirect.appendTo(file).file() == file &&
Redirect.appendTo(file).type() == Redirect.Type.APPEND



Params:
  • file – The File for the Redirect.
Returns:a redirect to append to the specified file
/**
         * Returns a redirect to append to the specified file.
         * Each write operation first advances the position to the
         * end of the file and then writes the requested data.
         * Whether the advancement of the position and the writing
         * of the data are done in a single atomic operation is
         * system-dependent and therefore unspecified.
         *
         * <p>It will always be true that
         *  <pre> {@code
         * Redirect.appendTo(file).file() == file &&
         * Redirect.appendTo(file).type() == Redirect.Type.APPEND
         * }</pre>
         *
         * @param file The {@code File} for the {@code Redirect}.
         * @return a redirect to append to the specified file
         */
        public static Redirect appendTo(final File file) {
            if (file == null)
                throw new NullPointerException();
            return new Redirect() {
                    public Type type() { return Type.APPEND; }
                    public File file() { return file; }
                    public String toString() {
                        return "redirect to append to file \"" + file + "\"";
                    }
                    boolean append() { return true; }
                };
        }

        
Compares the specified object with this Redirect for equality. Returns true if and only if the two objects are identical or both objects are Redirect instances of the same type associated with non-null equal File instances. 
/**
         * Compares the specified object with this {@code Redirect} for
         * equality.  Returns {@code true} if and only if the two
         * objects are identical or both objects are {@code Redirect}
         * instances of the same type associated with non-null equal
         * {@code File} instances.
         */
        public boolean equals(Object obj) {
            if (obj == this)
                return true;
            if (! (obj instanceof Redirect))
                return false;
            Redirect r = (Redirect) obj;
            if (r.type() != this.type())
                return false;
            assert this.file() != null;
            return this.file().equals(r.file());
        }

        
Returns a hash code value for this Redirect. 
Returns:a hash code value for this Redirect
/**
         * Returns a hash code value for this {@code Redirect}.
         * @return a hash code value for this {@code Redirect}
         */
        public int hashCode() {
            File file = file();
            if (file == null)
                return super.hashCode();
            else
                return file.hashCode();
        }

        
No public constructors. Clients must use predefined static Redirect instances or factory methods. 
/**
         * No public constructors.  Clients must use predefined
         * static {@code Redirect} instances or factory methods.
         */
        private Redirect() {}
    }

    
Private implementation subclass of Redirect that holds a FileDescriptor for the
output of a previously started Process.
The FileDescriptor is used as the standard input of the next Process
to be started.

/**
     * Private implementation subclass of Redirect that holds a FileDescriptor for the
     * output of a previously started Process.
     * The FileDescriptor is used as the standard input of the next Process
     * to be started.
     */
    static class RedirectPipeImpl extends Redirect {
        final FileDescriptor fd;

        RedirectPipeImpl() {
            this.fd = new FileDescriptor();
        }
        @Override
        public Type type() { return Type.PIPE; }

        @Override
        public String toString() { return type().toString();}

        FileDescriptor getFd() { return fd; }
    }

    
Return the array of redirects, creating the default as needed.

Returns:the array of redirects
/**
     * Return the array of redirects, creating the default as needed.
     * @return the array of redirects
     */
    private Redirect[] redirects() {
        if (redirects == null) {
            redirects = new Redirect[] {
                    Redirect.PIPE, Redirect.PIPE, Redirect.PIPE
            };
        }
        return redirects;
    }

    
Sets this process builder's standard input source. Subprocesses subsequently started by this object's start() method obtain their standard input from this source. 
If the source is Redirect.PIPE (the initial value), then the standard input of a subprocess can be written to using the output stream returned by Process.getOutputStream(). If the source is set to any other value, then Process.getOutputStream() will return a null output stream.

Params:
  • source – the new standard input source
Throws:
Returns:this process builder
Since: 1.7
/**
     * Sets this process builder's standard input source.
     *
     * Subprocesses subsequently started by this object's {@link #start()}
     * method obtain their standard input from this source.
     *
     * <p>If the source is {@link Redirect#PIPE Redirect.PIPE}
     * (the initial value), then the standard input of a
     * subprocess can be written to using the output stream
     * returned by {@link Process#getOutputStream()}.
     * If the source is set to any other value, then
     * {@link Process#getOutputStream()} will return a
     * <a href="#redirect-input">null output stream</a>.
     *
     * @param  source the new standard input source
     * @return this process builder
     * @throws IllegalArgumentException
     *         if the redirect does not correspond to a valid source
     *         of data, that is, has type
     *         {@link Redirect.Type#WRITE WRITE} or
     *         {@link Redirect.Type#APPEND APPEND}
     * @since  1.7
     */
    public ProcessBuilder redirectInput(Redirect source) {
        if (source.type() == Redirect.Type.WRITE ||
            source.type() == Redirect.Type.APPEND)
            throw new IllegalArgumentException(
                "Redirect invalid for reading: " + source);
        redirects()[0] = source;
        return this;
    }

    
Sets this process builder's standard output destination. Subprocesses subsequently started by this object's start() method send their standard output to this destination. 
If the destination is Redirect.PIPE (the initial value), then the standard output of a subprocess can be read using the input stream returned by Process.getInputStream(). If the destination is set to any other value, then Process.getInputStream() will return a null input stream.

Params:
  • destination – the new standard output destination
Throws:
Returns:this process builder
Since: 1.7
/**
     * Sets this process builder's standard output destination.
     *
     * Subprocesses subsequently started by this object's {@link #start()}
     * method send their standard output to this destination.
     *
     * <p>If the destination is {@link Redirect#PIPE Redirect.PIPE}
     * (the initial value), then the standard output of a subprocess
     * can be read using the input stream returned by {@link
     * Process#getInputStream()}.
     * If the destination is set to any other value, then
     * {@link Process#getInputStream()} will return a
     * <a href="#redirect-output">null input stream</a>.
     *
     * @param  destination the new standard output destination
     * @return this process builder
     * @throws IllegalArgumentException
     *         if the redirect does not correspond to a valid
     *         destination of data, that is, has type
     *         {@link Redirect.Type#READ READ}
     * @since  1.7
     */
    public ProcessBuilder redirectOutput(Redirect destination) {
        if (destination.type() == Redirect.Type.READ)
            throw new IllegalArgumentException(
                "Redirect invalid for writing: " + destination);
        redirects()[1] = destination;
        return this;
    }

    
Sets this process builder's standard error destination. Subprocesses subsequently started by this object's start() method send their standard error to this destination. 
If the destination is Redirect.PIPE (the initial value), then the error output of a subprocess can be read using the input stream returned by Process.getErrorStream(). If the destination is set to any other value, then Process.getErrorStream() will return a null input stream.

If the redirectErrorStream attribute has been set true, then the redirection set by this method has no effect. 
Params:
  • destination – the new standard error destination
Throws:
Returns:this process builder
Since: 1.7
/**
     * Sets this process builder's standard error destination.
     *
     * Subprocesses subsequently started by this object's {@link #start()}
     * method send their standard error to this destination.
     *
     * <p>If the destination is {@link Redirect#PIPE Redirect.PIPE}
     * (the initial value), then the error output of a subprocess
     * can be read using the input stream returned by {@link
     * Process#getErrorStream()}.
     * If the destination is set to any other value, then
     * {@link Process#getErrorStream()} will return a
     * <a href="#redirect-output">null input stream</a>.
     *
     * <p>If the {@link #redirectErrorStream() redirectErrorStream}
     * attribute has been set {@code true}, then the redirection set
     * by this method has no effect.
     *
     * @param  destination the new standard error destination
     * @return this process builder
     * @throws IllegalArgumentException
     *         if the redirect does not correspond to a valid
     *         destination of data, that is, has type
     *         {@link Redirect.Type#READ READ}
     * @since  1.7
     */
    public ProcessBuilder redirectError(Redirect destination) {
        if (destination.type() == Redirect.Type.READ)
            throw new IllegalArgumentException(
                "Redirect invalid for writing: " + destination);
        redirects()[2] = destination;
        return this;
    }

    
Sets this process builder's standard input source to a file.

This is a convenience method. An invocation of the form redirectInput(file) behaves in exactly the same way as the invocation redirectInput (Redirect.from(file)). 
Params:
  • file – the new standard input source
Returns:this process builder
Since: 1.7
/**
     * Sets this process builder's standard input source to a file.
     *
     * <p>This is a convenience method.  An invocation of the form
     * {@code redirectInput(file)}
     * behaves in exactly the same way as the invocation
     * {@link #redirectInput(Redirect) redirectInput}
     * {@code (Redirect.from(file))}.
     *
     * @param  file the new standard input source
     * @return this process builder
     * @since  1.7
     */
    public ProcessBuilder redirectInput(File file) {
        return redirectInput(Redirect.from(file));
    }

    
Sets this process builder's standard output destination to a file.

This is a convenience method. An invocation of the form redirectOutput(file) behaves in exactly the same way as the invocation redirectOutput (Redirect.to(file)). 
Params:
  • file – the new standard output destination
Returns:this process builder
Since: 1.7
/**
     * Sets this process builder's standard output destination to a file.
     *
     * <p>This is a convenience method.  An invocation of the form
     * {@code redirectOutput(file)}
     * behaves in exactly the same way as the invocation
     * {@link #redirectOutput(Redirect) redirectOutput}
     * {@code (Redirect.to(file))}.
     *
     * @param  file the new standard output destination
     * @return this process builder
     * @since  1.7
     */
    public ProcessBuilder redirectOutput(File file) {
        return redirectOutput(Redirect.to(file));
    }

    
Sets this process builder's standard error destination to a file.

This is a convenience method. An invocation of the form redirectError(file) behaves in exactly the same way as the invocation redirectError (Redirect.to(file)). 
Params:
  • file – the new standard error destination
Returns:this process builder
Since: 1.7
/**
     * Sets this process builder's standard error destination to a file.
     *
     * <p>This is a convenience method.  An invocation of the form
     * {@code redirectError(file)}
     * behaves in exactly the same way as the invocation
     * {@link #redirectError(Redirect) redirectError}
     * {@code (Redirect.to(file))}.
     *
     * @param  file the new standard error destination
     * @return this process builder
     * @since  1.7
     */
    public ProcessBuilder redirectError(File file) {
        return redirectError(Redirect.to(file));
    }

    
Returns this process builder's standard input source. Subprocesses subsequently started by this object's start() method obtain their standard input from this source. The initial value is Redirect.PIPE. 
Returns:this process builder's standard input source
Since: 1.7
/**
     * Returns this process builder's standard input source.
     *
     * Subprocesses subsequently started by this object's {@link #start()}
     * method obtain their standard input from this source.
     * The initial value is {@link Redirect#PIPE Redirect.PIPE}.
     *
     * @return this process builder's standard input source
     * @since  1.7
     */
    public Redirect redirectInput() {
        return (redirects == null) ? Redirect.PIPE : redirects[0];
    }

    
Returns this process builder's standard output destination. Subprocesses subsequently started by this object's start() method redirect their standard output to this destination. The initial value is Redirect.PIPE. 
Returns:this process builder's standard output destination
Since: 1.7
/**
     * Returns this process builder's standard output destination.
     *
     * Subprocesses subsequently started by this object's {@link #start()}
     * method redirect their standard output to this destination.
     * The initial value is {@link Redirect#PIPE Redirect.PIPE}.
     *
     * @return this process builder's standard output destination
     * @since  1.7
     */
    public Redirect redirectOutput() {
        return (redirects == null) ? Redirect.PIPE : redirects[1];
    }

    
Returns this process builder's standard error destination. Subprocesses subsequently started by this object's start() method redirect their standard error to this destination. The initial value is Redirect.PIPE. 
Returns:this process builder's standard error destination
Since: 1.7
/**
     * Returns this process builder's standard error destination.
     *
     * Subprocesses subsequently started by this object's {@link #start()}
     * method redirect their standard error to this destination.
     * The initial value is {@link Redirect#PIPE Redirect.PIPE}.
     *
     * @return this process builder's standard error destination
     * @since  1.7
     */
    public Redirect redirectError() {
        return (redirects == null) ? Redirect.PIPE : redirects[2];
    }

    
Sets the source and destination for subprocess standard I/O
to be the same as those of the current Java process.

This is a convenience method.  An invocation of the form
 
 
pb.inheritIO()


behaves in exactly the same way as the invocation
 
 
pb.redirectInput(Redirect.INHERIT)
  .redirectOutput(Redirect.INHERIT)
  .redirectError(Redirect.INHERIT)

 This gives behavior equivalent to most operating system command interpreters, or the standard C library function system(). 
Returns:this process builder
Since: 1.7
/**
     * Sets the source and destination for subprocess standard I/O
     * to be the same as those of the current Java process.
     *
     * <p>This is a convenience method.  An invocation of the form
     *  <pre> {@code
     * pb.inheritIO()
     * }</pre>
     * behaves in exactly the same way as the invocation
     *  <pre> {@code
     * pb.redirectInput(Redirect.INHERIT)
     *   .redirectOutput(Redirect.INHERIT)
     *   .redirectError(Redirect.INHERIT)
     * }</pre>
     *
     * This gives behavior equivalent to most operating system
     * command interpreters, or the standard C library function
     * {@code system()}.
     *
     * @return this process builder
     * @since  1.7
     */
    public ProcessBuilder inheritIO() {
        Arrays.fill(redirects(), Redirect.INHERIT);
        return this;
    }

    
Tells whether this process builder merges standard error and
standard output.

If this property is true, then any error output generated by subprocesses subsequently started by this object's start() method will be merged with the standard output, so that both can be read using the Process.getInputStream() method. This makes it easier to correlate error messages with the corresponding output. The initial value is false. 
Returns:this process builder's redirectErrorStream property
/**
     * Tells whether this process builder merges standard error and
     * standard output.
     *
     * <p>If this property is {@code true}, then any error output
     * generated by subprocesses subsequently started by this object's
     * {@link #start()} method will be merged with the standard
     * output, so that both can be read using the
     * {@link Process#getInputStream()} method.  This makes it easier
     * to correlate error messages with the corresponding output.
     * The initial value is {@code false}.
     *
     * @return this process builder's {@code redirectErrorStream} property
     */
    public boolean redirectErrorStream() {
        return redirectErrorStream;
    }

    
Sets this process builder's redirectErrorStream property. 
If this property is true, then any error output generated by subprocesses subsequently started by this object's start() method will be merged with the standard output, so that both can be read using the Process.getInputStream() method. This makes it easier to correlate error messages with the corresponding output. The initial value is false. 
Params:
  • redirectErrorStream – the new property value
Returns:this process builder
/**
     * Sets this process builder's {@code redirectErrorStream} property.
     *
     * <p>If this property is {@code true}, then any error output
     * generated by subprocesses subsequently started by this object's
     * {@link #start()} method will be merged with the standard
     * output, so that both can be read using the
     * {@link Process#getInputStream()} method.  This makes it easier
     * to correlate error messages with the corresponding output.
     * The initial value is {@code false}.
     *
     * @param  redirectErrorStream the new property value
     * @return this process builder
     */
    public ProcessBuilder redirectErrorStream(boolean redirectErrorStream) {
        this.redirectErrorStream = redirectErrorStream;
        return this;
    }

    
Starts a new process using the attributes of this process builder.

The new process will invoke the command and arguments given by command(), in a working directory as given by directory(), with a process environment as given by environment(). 
This method checks that the command is a valid operating
system command.  Which commands are valid is system-dependent,
but at the very least the command must be a non-empty list of
non-null strings.

A minimal set of system dependent environment variables may be required to start a process on some operating systems. As a result, the subprocess may inherit additional environment variable settings beyond those in the process builder's environment(). 
If there is a security manager, its checkExec method is called with the first component of this object's command array as its argument. This may result in a SecurityException being thrown. 
Starting an operating system process is highly system-dependent.
Among the many things that can go wrong are:

    

  • The operating system program file was not found.

  • Access to the program file was denied.

  • The working directory does not exist.

  • Invalid character in command argument, such as NUL.



In such cases an exception will be thrown. The exact nature of the exception is system-dependent, but it will always be a subclass of IOException. 
If the operating system does not support the creation of processes, an UnsupportedOperationException will be thrown. 
Subsequent modifications to this process builder will not affect the returned Process. 
Throws:
See Also:
Returns:a new Process object for managing the subprocess
/**
     * Starts a new process using the attributes of this process builder.
     *
     * <p>The new process will
     * invoke the command and arguments given by {@link #command()},
     * in a working directory as given by {@link #directory()},
     * with a process environment as given by {@link #environment()}.
     *
     * <p>This method checks that the command is a valid operating
     * system command.  Which commands are valid is system-dependent,
     * but at the very least the command must be a non-empty list of
     * non-null strings.
     *
     * <p>A minimal set of system dependent environment variables may
     * be required to start a process on some operating systems.
     * As a result, the subprocess may inherit additional environment variable
     * settings beyond those in the process builder's {@link #environment()}.
     *
     * <p>If there is a security manager, its
     * {@link SecurityManager#checkExec checkExec}
     * method is called with the first component of this object's
     * {@code command} array as its argument. This may result in
     * a {@link SecurityException} being thrown.
     *
     * <p>Starting an operating system process is highly system-dependent.
     * Among the many things that can go wrong are:
     * <ul>
     * <li>The operating system program file was not found.
     * <li>Access to the program file was denied.
     * <li>The working directory does not exist.
     * <li>Invalid character in command argument, such as NUL.
     * </ul>
     *
     * <p>In such cases an exception will be thrown.  The exact nature
     * of the exception is system-dependent, but it will always be a
     * subclass of {@link IOException}.
     *
     * <p>If the operating system does not support the creation of
     * processes, an {@link UnsupportedOperationException} will be thrown.
     *
     * <p>Subsequent modifications to this process builder will not
     * affect the returned {@link Process}.
     *
     * @return a new {@link Process} object for managing the subprocess
     *
     * @throws NullPointerException
     *         if an element of the command list is null
     *
     * @throws IndexOutOfBoundsException
     *         if the command is an empty list (has size {@code 0})
     *
     * @throws SecurityException
     *         if a security manager exists and
     *         <ul>
     *
     *         <li>its
     *         {@link SecurityManager#checkExec checkExec}
     *         method doesn't allow creation of the subprocess, or
     *
     *         <li>the standard input to the subprocess was
     *         {@linkplain #redirectInput redirected from a file}
     *         and the security manager's
     *         {@link SecurityManager#checkRead(String) checkRead} method
     *         denies read access to the file, or
     *
     *         <li>the standard output or standard error of the
     *         subprocess was
     *         {@linkplain #redirectOutput redirected to a file}
     *         and the security manager's
     *         {@link SecurityManager#checkWrite(String) checkWrite} method
     *         denies write access to the file
     *
     *         </ul>
     *
     * @throws  UnsupportedOperationException
     *          If the operating system does not support the creation of processes.
     *
     * @throws IOException if an I/O error occurs
     *
     * @see Runtime#exec(String[], String[], java.io.File)
     */
    public Process start() throws IOException {
        return start(redirects);
    }

    
Start a new Process using an explicit array of redirects. See start for details of starting each Process. 
Params:
  • redirect – array of redirects for stdin, stdout, stderr
Throws:
Returns:the new Process
/**
     * Start a new Process using an explicit array of redirects.
     * See {@link #start} for details of starting each Process.
     *
     * @param redirect array of redirects for stdin, stdout, stderr
     * @return the new Process
     * @throws IOException if an I/O error occurs
     */
    private Process start(Redirect[] redirects) throws IOException {
        // Must convert to array first -- a malicious user-supplied
        // list might try to circumvent the security check.
        String[] cmdarray = command.toArray(new String[command.size()]);
        cmdarray = cmdarray.clone();

        for (String arg : cmdarray)
            if (arg == null)
                throw new NullPointerException();
        // Throws IndexOutOfBoundsException if command is empty
        String prog = cmdarray[0];

        SecurityManager security = System.getSecurityManager();
        if (security != null)
            security.checkExec(prog);

        String dir = directory == null ? null : directory.toString();

        for (int i = 1; i < cmdarray.length; i++) {
            if (cmdarray[i].indexOf('\u0000') >= 0) {
                throw new IOException("invalid null character in command");
            }
        }

        try {
            return ProcessImpl.start(cmdarray,
                                     environment,
                                     dir,
                                     redirects,
                                     redirectErrorStream);
        } catch (IOException | IllegalArgumentException e) {
            String exceptionInfo = ": " + e.getMessage();
            Throwable cause = e;
            if ((e instanceof IOException) && security != null) {
                // Can not disclose the fail reason for read-protected files.
                try {
                    security.checkRead(prog);
                } catch (SecurityException se) {
                    exceptionInfo = "";
                    cause = se;
                }
            }
            // It's much easier for us to create a high-quality error
            // message than the low-level C code which found the problem.
            throw new IOException(
                "Cannot run program \"" + prog + "\""
                + (dir == null ? "" : " (in directory \"" + dir + "\")")
                + exceptionInfo,
                cause);
        }
    }

    
Starts a Process for each ProcessBuilder, creating a pipeline of processes linked by their standard output and standard input streams. The attributes of each ProcessBuilder are used to start the respective process except that as each process is started, its standard output is directed to the standard input of the next. The redirects for standard input of the first process and standard output of the last process are initialized using the redirect settings of the respective ProcessBuilder. All other ProcessBuilder redirects should be Redirect.PIPE. 
 All input and output streams between the intermediate processes are not accessible. The standard input of all processes except the first process are null output streams The standard output of all processes except the last process are null input streams.

 The redirectErrorStream() of each ProcessBuilder applies to the respective process. If set to true, the error stream is written to the same stream as standard output. 

If starting any of the processes throws an Exception, all processes
are forcibly destroyed.

 The startPipeline method performs the same checks on each ProcessBuilder as does the start method. The new process will invoke the command and arguments given by command(), in a working directory as given by directory(), with a process environment as given by environment(). 

This method checks that the command is a valid operating
system command.  Which commands are valid is system-dependent,
but at the very least the command must be a non-empty list of
non-null strings.

 A minimal set of system dependent environment variables may be required to start a process on some operating systems. As a result, the subprocess may inherit additional environment variable settings beyond those in the process builder's environment(). 
 If there is a security manager, its checkExec method is called with the first component of this object's command array as its argument. This may result in a SecurityException being thrown. 

Starting an operating system process is highly system-dependent.
Among the many things that can go wrong are:

    

  • The operating system program file was not found.

  • Access to the program file was denied.

  • The working directory does not exist.

  • Invalid character in command argument, such as NUL.



 In such cases an exception will be thrown. The exact nature of the exception is system-dependent, but it will always be a subclass of IOException. 
 If the operating system does not support the creation of processes, an UnsupportedOperationException will be thrown. 
 Subsequent modifications to this process builder will not affect the returned Process. 
Params:
  • builders – a List of ProcessBuilders
Throws:
API Note:
For example to count the unique imports for all the files in a file hierarchy
on a Unix compatible platform:


String directory = "/home/duke/src";
ProcessBuilder[] builders = {
             new ProcessBuilder("find", directory, "-type", "f"),
new ProcessBuilder("xargs", "grep", "-h", "^import "),
new ProcessBuilder("awk", "{print $2;}"),
new ProcessBuilder("sort", "-u")};
List<Process> processes = ProcessBuilder.startPipeline(
        Arrays.asList(builders));
Process last = processes.get(processes.size()-1);
try (InputStream is = last.getInputStream();
        Reader isr = new InputStreamReader(is);
        BufferedReader r = new BufferedReader(isr)) {
    long count = r.lines().count();
 }

Returns:a List<Process>es started from the corresponding ProcessBuilder
Since:9
/**
     * Starts a Process for each ProcessBuilder, creating a pipeline of
     * processes linked by their standard output and standard input streams.
     * The attributes of each ProcessBuilder are used to start the respective
     * process except that as each process is started, its standard output
     * is directed to the standard input of the next.  The redirects for standard
     * input of the first process and standard output of the last process are
     * initialized using the redirect settings of the respective ProcessBuilder.
     * All other {@code ProcessBuilder} redirects should be
     * {@link Redirect#PIPE Redirect.PIPE}.
     * <p>
     * All input and output streams between the intermediate processes are
     * not accessible.
     * The {@link Process#getOutputStream standard input} of all processes
     * except the first process are <i>null output streams</i>
     * The {@link Process#getInputStream standard output} of all processes
     * except the last process are <i>null input streams</i>.
     * <p>
     * The {@link #redirectErrorStream()} of each ProcessBuilder applies to the
     * respective process.  If set to {@code true}, the error stream is written
     * to the same stream as standard output.
     * <p>
     * If starting any of the processes throws an Exception, all processes
     * are forcibly destroyed.
     * <p>
     * The {@code startPipeline} method performs the same checks on
     * each ProcessBuilder as does the {@link #start} method. The new process
     * will invoke the command and arguments given by {@link #command()},
     * in a working directory as given by {@link #directory()},
     * with a process environment as given by {@link #environment()}.
     * <p>
     * This method checks that the command is a valid operating
     * system command.  Which commands are valid is system-dependent,
     * but at the very least the command must be a non-empty list of
     * non-null strings.
     * <p>
     * A minimal set of system dependent environment variables may
     * be required to start a process on some operating systems.
     * As a result, the subprocess may inherit additional environment variable
     * settings beyond those in the process builder's {@link #environment()}.
     * <p>
     * If there is a security manager, its
     * {@link SecurityManager#checkExec checkExec}
     * method is called with the first component of this object's
     * {@code command} array as its argument. This may result in
     * a {@link SecurityException} being thrown.
     * <p>
     * Starting an operating system process is highly system-dependent.
     * Among the many things that can go wrong are:
     * <ul>
     * <li>The operating system program file was not found.
     * <li>Access to the program file was denied.
     * <li>The working directory does not exist.
     * <li>Invalid character in command argument, such as NUL.
     * </ul>
     * <p>
     * In such cases an exception will be thrown.  The exact nature
     * of the exception is system-dependent, but it will always be a
     * subclass of {@link IOException}.
     * <p>
     * If the operating system does not support the creation of
     * processes, an {@link UnsupportedOperationException} will be thrown.
     * <p>
     * Subsequent modifications to this process builder will not
     * affect the returned {@link Process}.
     * @apiNote
     * For example to count the unique imports for all the files in a file hierarchy
     * on a Unix compatible platform:
     * <pre>{@code
     * String directory = "/home/duke/src";
     * ProcessBuilder[] builders = {
     *              new ProcessBuilder("find", directory, "-type", "f"),
                    new ProcessBuilder("xargs", "grep", "-h", "^import "),
                    new ProcessBuilder("awk", "{print $2;}"),
                    new ProcessBuilder("sort", "-u")};
     * List<Process> processes = ProcessBuilder.startPipeline(
     *         Arrays.asList(builders));
     * Process last = processes.get(processes.size()-1);
     * try (InputStream is = last.getInputStream();
     *         Reader isr = new InputStreamReader(is);
     *         BufferedReader r = new BufferedReader(isr)) {
     *     long count = r.lines().count();
     * }
     * }</pre>
     *
     * @param builders a List of ProcessBuilders
     * @return a {@code List<Process>}es started from the corresponding
     *         ProcessBuilder
     * @throws IllegalArgumentException any of the redirects except the
     *          standard input of the first builder and the standard output of
     *          the last builder are not {@link Redirect#PIPE}.
     * @throws NullPointerException
     *         if an element of the command list is null or
     *         if an element of the ProcessBuilder list is null or
     *         the builders argument is null
     * @throws IndexOutOfBoundsException
     *         if the command is an empty list (has size {@code 0})
     * @throws SecurityException
     *         if a security manager exists and
     *         <ul>
     *         <li>its
     *         {@link SecurityManager#checkExec checkExec}
     *         method doesn't allow creation of the subprocess, or
     *         <li>the standard input to the subprocess was
     *         {@linkplain #redirectInput redirected from a file}
     *         and the security manager's
     *         {@link SecurityManager#checkRead(String) checkRead} method
     *         denies read access to the file, or
     *         <li>the standard output or standard error of the
     *         subprocess was
     *         {@linkplain #redirectOutput redirected to a file}
     *         and the security manager's
     *         {@link SecurityManager#checkWrite(String) checkWrite} method
     *         denies write access to the file
     *         </ul>
     *
     * @throws  UnsupportedOperationException
     *          If the operating system does not support the creation of processes
     *
     * @throws IOException if an I/O error occurs
     * @since 9
     */
    public static List<Process> startPipeline(List<ProcessBuilder> builders) throws IOException {
        // Accumulate and check the builders
        final int numBuilders = builders.size();
        List<Process> processes = new ArrayList<>(numBuilders);
        try {
            Redirect prevOutput = null;
            for (int index = 0; index < builders.size(); index++) {
                ProcessBuilder builder = builders.get(index);
                Redirect[] redirects = builder.redirects();
                if (index > 0) {
                    // check the current Builder to see if it can take input from the previous
                    if (builder.redirectInput() != Redirect.PIPE) {
                        throw new IllegalArgumentException("builder redirectInput()" +
                                " must be PIPE except for the first builder: "
                                + builder.redirectInput());
                    }
                    redirects[0] = prevOutput;
                }
                if (index < numBuilders - 1) {
                    // check all but the last stage has output = PIPE
                    if (builder.redirectOutput() != Redirect.PIPE) {
                        throw new IllegalArgumentException("builder redirectOutput()" +
                                " must be PIPE except for the last builder: "
                                + builder.redirectOutput());
                    }
                    redirects[1] = new RedirectPipeImpl();  // placeholder for new output
                }
                processes.add(builder.start(redirects));
                prevOutput = redirects[1];
            }
        } catch (Exception ex) {
            // Cleanup processes already started
            processes.forEach(Process::destroyForcibly);
            processes.forEach(p -> {
                try {
                    p.waitFor();        // Wait for it to exit
                } catch (InterruptedException ie) {
                    // If interrupted; continue with next Process
                    Thread.currentThread().interrupt();
                }
            });
            throw ex;
        }
        return processes;
    }
}