https://openjdk.java.net/ 
/*
 * Copyright (c) 2014, 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 jdk.jshell;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URI;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.TreeMap;

import javax.tools.JavaFileObject.Kind;
import static javax.tools.StandardLocation.CLASS_PATH;
import javax.tools.FileObject;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardLocation;


import static jdk.internal.jshell.debug.InternalDebugControl.DBG_FMGR;


File manager for the compiler API.  Reads from memory (Strings) and writes
class files to memory (cached OutputMemoryJavaFileObject).

Author:Robert Field
/**
 * File manager for the compiler API.  Reads from memory (Strings) and writes
 * class files to memory (cached OutputMemoryJavaFileObject).
 *
 * @author Robert Field
 */
class MemoryFileManager implements JavaFileManager {

    private final StandardJavaFileManager stdFileManager;

    private final Map<String, OutputMemoryJavaFileObject> classObjects = new TreeMap<>();

    private ClassFileCreationListener classListener = null;

    private final JShell proc;

    Iterable<? extends Path> getLocationAsPaths(Location loc) {
        return this.stdFileManager.getLocationAsPaths(loc);
    }

    static abstract class MemoryJavaFileObject extends SimpleJavaFileObject {

        public MemoryJavaFileObject(String name, JavaFileObject.Kind kind) {
            super(URI.create("string:///" + name.replace('.', '/')
                    + kind.extension), kind);
        }
    }

    class SourceMemoryJavaFileObject extends MemoryJavaFileObject {
        private final String src;
        private final Object origin;

        SourceMemoryJavaFileObject(Object origin, String className, String code) {
            super(className, JavaFileObject.Kind.SOURCE);
            this.origin = origin;
            this.src = code;
        }

        public Object getOrigin() {
            return origin;
        }

        @Override
        public CharSequence getCharContent(boolean ignoreEncodingErrors) {
            return src;
        }
    }

    static class OutputMemoryJavaFileObject extends MemoryJavaFileObject {

        
Byte code created by the compiler will be stored in this
ByteArrayOutputStream.

/**
         * Byte code created by the compiler will be stored in this
         * ByteArrayOutputStream.
         */
        private ByteArrayOutputStream bos = new ByteArrayOutputStream();
        private byte[] bytes = null;

        private final String className;

        public OutputMemoryJavaFileObject(String name, JavaFileObject.Kind kind) {
            super(name, kind);
            this.className = name;
        }

        public byte[] getBytes() {
            if (bytes == null) {
                bytes = bos.toByteArray();
                bos = null;
            }
            return bytes;
        }

        public void dump() {
            try {
                Path dumpDir = FileSystems.getDefault().getPath("dump");
                if (Files.notExists(dumpDir)) {
                    Files.createDirectory(dumpDir);
                }
                Path file = FileSystems.getDefault().getPath("dump", getName() + ".class");
                Files.write(file, getBytes());
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            }
        }

        @Override
        public String getName() {
            return className;
        }

        
Will provide the compiler with an output stream that leads to our
byte array.

/**
         * Will provide the compiler with an output stream that leads to our
         * byte array.
         */
        @Override
        public OutputStream openOutputStream() throws IOException {
            return bos;
        }

        @Override
        public InputStream openInputStream() throws IOException {
            return new ByteArrayInputStream(getBytes());
        }
    }

    public MemoryFileManager(StandardJavaFileManager standardManager, JShell proc) {
        this.stdFileManager = proc.fileManagerMapping != null
                ? proc.fileManagerMapping.apply(standardManager)
                : standardManager;
        this.proc = proc;
    }

    private Collection<OutputMemoryJavaFileObject> generatedClasses() {
        return classObjects.values();
    }

    // For debugging dumps
    public void dumpClasses() {
        for (OutputMemoryJavaFileObject co : generatedClasses()) {
            co.dump();
        }
    }

    public JavaFileObject createSourceFileObject(Object origin, String name, String code) {
        return new SourceMemoryJavaFileObject(origin, name, code);
    }

    
Returns a class loader for loading plug-ins from the given location. For example, to load annotation processors, a compiler will request a class loader for the 
ANNOTATION_PROCESSOR_PATH location. 
Params:
  • location – a location
Throws:
Returns:a class loader for the given location; or null if loading plug-ins from the given location is disabled or if the location is not known
/**
     * Returns a class loader for loading plug-ins from the given location. For
     * example, to load annotation processors, a compiler will request a class
     * loader for the {@link
     * StandardLocation#ANNOTATION_PROCESSOR_PATH
     * ANNOTATION_PROCESSOR_PATH} location.
     *
     * @param location a location
     * @return a class loader for the given location; or {@code null}
     * if loading plug-ins from the given location is disabled or if
     * the location is not known
     * @throws SecurityException if a class loader can not be created
     * in the current security context
     * @throws IllegalStateException if {@link #close} has been called
     * and this file manager cannot be reopened
     */
    @Override
    public ClassLoader getClassLoader(JavaFileManager.Location location) {
        proc.debug(DBG_FMGR, "getClassLoader: location\n", location);
        return stdFileManager.getClassLoader(location);
    }

    
Lists all file objects matching the given criteria in the given
location.  List file objects in "subpackages" if recurse is
true.

Note: even if the given location is unknown to this file manager, it may not return null. Also, an unknown location may not cause an exception. 
Params:
  • location –     a location
  • packageName –  a package name
  • kinds –        return objects only of these kinds
  • recurse –      if true include "subpackages"
Throws:
Returns:an Iterable of file objects matching the given criteria
/**
     * Lists all file objects matching the given criteria in the given
     * location.  List file objects in "subpackages" if recurse is
     * true.
     *
     * <p>Note: even if the given location is unknown to this file
     * manager, it may not return {@code null}.  Also, an unknown
     * location may not cause an exception.
     *
     * @param location     a location
     * @param packageName  a package name
     * @param kinds        return objects only of these kinds
     * @param recurse      if true include "subpackages"
     * @return an Iterable of file objects matching the given criteria
     * @throws IOException if an I/O error occurred, or if {@link
     * #close} has been called and this file manager cannot be
     * reopened
     * @throws IllegalStateException if {@link #close} has been called
     * and this file manager cannot be reopened
     */
    @Override
    public Iterable<JavaFileObject> list(JavaFileManager.Location location,
            String packageName,
            Set<JavaFileObject.Kind> kinds,
            boolean recurse)
            throws IOException {
        Iterable<JavaFileObject> stdList = stdFileManager.list(location, packageName, kinds, recurse);
        if (location==CLASS_PATH && packageName.equals("REPL")) {
            // if the desired list is for our JShell package, lazily iterate over
            // first the standard list then any generated classes.
            return () -> new Iterator<JavaFileObject>() {
                boolean stdDone = false;
                Iterator<? extends JavaFileObject> it;

                @Override
                public boolean hasNext() {
                    if (it == null) {
                        it = stdList.iterator();
                    }
                    if (it.hasNext()) {
                        return true;
                    }
                    if (stdDone) {
                        return false;
                    } else {
                        stdDone = true;
                        it = generatedClasses().iterator();
                        return it.hasNext();
                    }
                }

                @Override
                public JavaFileObject next() {
                    if (!hasNext()) {
                        throw new NoSuchElementException();
                    }
                    return it.next();
                }

            };
        } else {
            return stdList;
        }
    }

    
Infers a binary name of a file object based on a location.  The
binary name returned might not be a valid binary name according to
The Java&trade {        throw new UnsupportedOperationException("Not supported yet.");  } Language Specification.

Params:
  • location – a location
  • file – a file object
Throws:
Returns:a binary name or null the file object is not found in the given location
/**
     * Infers a binary name of a file object based on a location.  The
     * binary name returned might not be a valid binary name according to
     * <cite>The Java&trade {        throw new UnsupportedOperationException("Not supported yet.");  } Language Specification</cite>.
     *
     * @param location a location
     * @param file a file object
     * @return a binary name or {@code null} the file object is not
     * found in the given location
     * @throws IllegalStateException if {@link #close} has been called
     * and this file manager cannot be reopened
     */
    @Override
    public String inferBinaryName(JavaFileManager.Location location, JavaFileObject file) {
        if (file instanceof OutputMemoryJavaFileObject) {
            OutputMemoryJavaFileObject ofo = (OutputMemoryJavaFileObject) file;
            proc.debug(DBG_FMGR, "inferBinaryName %s => %s\n", file, ofo.getName());
            return ofo.getName();
        } else {
            return stdFileManager.inferBinaryName(location, file);
        }
    }

    
Compares two file objects and return true if they represent the
same underlying object.

Params:
  • a – a file object
  • b – a file object
Throws:
  • IllegalArgumentException – if either of the arguments
were created with another file manager and this file manager
does not support foreign file objects
Returns:true if the given file objects represent the same
underlying object
/**
     * Compares two file objects and return true if they represent the
     * same underlying object.
     *
     * @param a a file object
     * @param b a file object
     * @return true if the given file objects represent the same
     * underlying object
     *
     * @throws IllegalArgumentException if either of the arguments
     * were created with another file manager and this file manager
     * does not support foreign file objects
     */
    @Override
    public boolean isSameFile(FileObject a, FileObject b) {
        return stdFileManager.isSameFile(b, b);
    }

    
Determines if the given option is supported and if so, the
number of arguments the option takes.

Params:
  • option – an option
Returns:the number of arguments the given option takes or -1 if
the option is not supported
/**
     * Determines if the given option is supported and if so, the
     * number of arguments the option takes.
     *
     * @param option an option
     * @return the number of arguments the given option takes or -1 if
     * the option is not supported
     */
    @Override
    public int isSupportedOption(String option) {
        proc.debug(DBG_FMGR, "isSupportedOption: %s\n", option);
        return stdFileManager.isSupportedOption(option);
    }

    
Handles one option. If current is an option to this file manager it will consume any arguments to that option from remaining and return true, otherwise return false. 
Params:
  • current – current option
  • remaining – remaining options
Throws:
Returns:true if this option was handled by this file manager,
false otherwise
/**
     * Handles one option.  If {@code current} is an option to this
     * file manager it will consume any arguments to that option from
     * {@code remaining} and return true, otherwise return false.
     *
     * @param current current option
     * @param remaining remaining options
     * @return true if this option was handled by this file manager,
     * false otherwise
     * @throws IllegalArgumentException if this option to this file
     * manager is used incorrectly
     * @throws IllegalStateException if {@link #close} has been called
     * and this file manager cannot be reopened
     */
    @Override
    public boolean handleOption(String current, Iterator<String> remaining) {
        proc.debug(DBG_FMGR, "handleOption: current: %s\n", current +
                ", remaining: " + remaining);
        return stdFileManager.handleOption(current, remaining);
    }

    
Determines if a location is known to this file manager.

Params:
  • location – a location
Returns:true if the location is known
/**
     * Determines if a location is known to this file manager.
     *
     * @param location a location
     * @return true if the location is known
     */
    @Override
    public boolean hasLocation(JavaFileManager.Location location) {
        proc.debug(DBG_FMGR, "hasLocation: location: %s\n", location);
        return stdFileManager.hasLocation(location);
    }

    interface ClassFileCreationListener {
        void newClassFile(OutputMemoryJavaFileObject jfo, JavaFileManager.Location location,
                String className, Kind kind, FileObject sibling);
    }

    void registerClassFileCreationListener(ClassFileCreationListener listen) {
        this.classListener = listen;
    }

    
Returns a file object for input representing the specified class of the specified kind in the given location. 
Params:
  • location – a location
  • className – the name of a class
  • kind – the kind of file, must be one of SOURCE or CLASS
Throws:
  • IllegalArgumentException – if the location is not known
to this file manager and the file manager does not support
unknown locations, or if the kind is not valid
  • IOException – if an I/O error occurred, or if close has been called and this file manager cannot be reopened
  • IllegalStateException – if close has been called and this file manager cannot be reopened
Returns:a file object, might return null if the file does not exist
/**
     * Returns a {@linkplain JavaFileObject file object} for input
     * representing the specified class of the specified kind in the
     * given location.
     *
     * @param location a location
     * @param className the name of a class
     * @param kind the kind of file, must be one of {@link
     * JavaFileObject.Kind#SOURCE SOURCE} or {@link
     * JavaFileObject.Kind#CLASS CLASS}
     * @return a file object, might return {@code null} if the
     * file does not exist
     * @throws IllegalArgumentException if the location is not known
     * to this file manager and the file manager does not support
     * unknown locations, or if the kind is not valid
     * @throws IOException if an I/O error occurred, or if {@link
     * #close} has been called and this file manager cannot be
     * reopened
     * @throws IllegalStateException if {@link #close} has been called
     * and this file manager cannot be reopened
     */
    @Override
    public JavaFileObject getJavaFileForInput(JavaFileManager.Location location,
            String className,
            JavaFileObject.Kind kind)
            throws IOException {
        return stdFileManager.getJavaFileForInput(location, className, kind);
    }

    
Returns a file object for output representing the specified class of the specified kind in the given location. 
Optionally, this file manager might consider the sibling as
a hint for where to place the output.  The exact semantics of
this hint is unspecified.  The JDK compiler, javac, for
example, will place class files in the same directories as
originating source files unless a class file output directory
is provided.  To facilitate this behavior, javac might provide
the originating source file as sibling when calling this
method.

Params:
  • location – a location
  • className – the name of a class
  • kind – the kind of file, must be one of SOURCE or CLASS
  • sibling – a file object to be used as hint for placement; might be null
Throws:
  • IllegalArgumentException – if sibling is not known to
this file manager, or if the location is not known to this file
manager and the file manager does not support unknown
locations, or if the kind is not valid
  • IOException – if an I/O error occurred, or if close has been called and this file manager cannot be reopened
  • IllegalStateException – close has been called and this file manager cannot be reopened
Returns:a file object for output
/**
     * Returns a {@linkplain JavaFileObject file object} for output
     * representing the specified class of the specified kind in the
     * given location.
     *
     * <p>Optionally, this file manager might consider the sibling as
     * a hint for where to place the output.  The exact semantics of
     * this hint is unspecified.  The JDK compiler, javac, for
     * example, will place class files in the same directories as
     * originating source files unless a class file output directory
     * is provided.  To facilitate this behavior, javac might provide
     * the originating source file as sibling when calling this
     * method.
     *
     * @param location a location
     * @param className the name of a class
     * @param kind the kind of file, must be one of {@link
     * JavaFileObject.Kind#SOURCE SOURCE} or {@link
     * JavaFileObject.Kind#CLASS CLASS}
     * @param sibling a file object to be used as hint for placement;
     * might be {@code null}
     * @return a file object for output
     * @throws IllegalArgumentException if sibling is not known to
     * this file manager, or if the location is not known to this file
     * manager and the file manager does not support unknown
     * locations, or if the kind is not valid
     * @throws IOException if an I/O error occurred, or if {@link
     * #close} has been called and this file manager cannot be
     * reopened
     * @throws IllegalStateException {@link #close} has been called
     * and this file manager cannot be reopened
     */
    @Override
    public JavaFileObject getJavaFileForOutput(JavaFileManager.Location location,
            String className, Kind kind, FileObject sibling) throws IOException {

        OutputMemoryJavaFileObject fo;
        fo = new OutputMemoryJavaFileObject(className, kind);
        classObjects.put(className, fo);
        proc.debug(DBG_FMGR, "Set out file: %s = %s\n", className, fo);
        if (classListener != null) {
            classListener.newClassFile(fo, location, className, kind, sibling);
        }
        return fo;
    }

    
Returns a file object for input representing the specified relative
name in the specified package in the given location.

If the returned object represents a source or class file, it must be an instance of JavaFileObject. 
Informally, the file object returned by this method is located in the concatenation of the location, package name, and relative name. For example, to locate the properties file "resources/compiler.properties" in the package "com.sun.tools.javac" in the SOURCE_PATH location, this method might be called like so: 
getFileForInput(SOURCE_PATH, "com.sun.tools.javac", "resources/compiler.properties");


If the call was executed on Windows, with SOURCE_PATH set to
"C:\Documents and Settings\UncleBob\src\share\classes",
a valid result would be a file object representing the file
"C:\Documents and Settings\UncleBob\src\share\classes\com\sun\tools\javac\resources\compiler.properties".

Params:
  • location – a location
  • packageName – a package name
  • relativeName – a relative name
Throws:
  • IllegalArgumentException – if the location is not known to this file manager and the file manager does not support unknown locations, or if relativeName is not valid
  • IOException – if an I/O error occurred, or if close has been called and this file manager cannot be reopened
  • IllegalStateException – if close has been called and this file manager cannot be reopened
Returns:a file object, might return null if the file does not exist
/**
     * Returns a {@linkplain FileObject file object} for input
     * representing the specified <a href="JavaFileManager.html#relative_name">relative
     * name</a> in the specified package in the given location.
     *
     * <p>If the returned object represents a {@linkplain
     * JavaFileObject.Kind#SOURCE source} or {@linkplain
     * JavaFileObject.Kind#CLASS class} file, it must be an instance
     * of {@link JavaFileObject}.
     *
     * <p>Informally, the file object returned by this method is
     * located in the concatenation of the location, package name, and
     * relative name.  For example, to locate the properties file
     * "resources/compiler.properties" in the package
     * "com.sun.tools.javac" in the {@linkplain
     * StandardLocation#SOURCE_PATH SOURCE_PATH} location, this method
     * might be called like so:
     *
     * <pre>getFileForInput(SOURCE_PATH, "com.sun.tools.javac", "resources/compiler.properties");</pre>
     *
     * <p>If the call was executed on Windows, with SOURCE_PATH set to
     * <code>"C:\Documents&nbsp;and&nbsp;Settings\UncleBob\src\share\classes"</code>,
     * a valid result would be a file object representing the file
     * <code>"C:\Documents&nbsp;and&nbsp;Settings\UncleBob\src\share\classes\com\sun\tools\javac\resources\compiler.properties"</code>.
     *
     * @param location a location
     * @param packageName a package name
     * @param relativeName a relative name
     * @return a file object, might return {@code null} if the file
     * does not exist
     * @throws IllegalArgumentException if the location is not known
     * to this file manager and the file manager does not support
     * unknown locations, or if {@code relativeName} is not valid
     * @throws IOException if an I/O error occurred, or if {@link
     * #close} has been called and this file manager cannot be
     * reopened
     * @throws IllegalStateException if {@link #close} has been called
     * and this file manager cannot be reopened
     */
    @Override
    public FileObject getFileForInput(JavaFileManager.Location location,
            String packageName,
            String relativeName)
            throws IOException {
        proc.debug(DBG_FMGR, "getFileForInput location=%s packageName=%s\n", location, packageName);
        return stdFileManager.getFileForInput(location, packageName, relativeName);
    }

    
Returns a file object for output representing the specified relative
name in the specified package in the given location.

Optionally, this file manager might consider the sibling as
a hint for where to place the output.  The exact semantics of
this hint is unspecified.  The JDK compiler, javac, for
example, will place class files in the same directories as
originating source files unless a class file output directory
is provided.  To facilitate this behavior, javac might provide
the originating source file as sibling when calling this
method.

If the returned object represents a source or class file, it must be an instance of JavaFileObject. 
Informally, the file object returned by this method is located in the concatenation of the location, package name, and relative name or next to the sibling argument. See getFileForInput for an example. 
Params:
  • location – a location
  • packageName – a package name
  • relativeName – a relative name
  • sibling – a file object to be used as hint for placement; might be null
Throws:
  • IllegalArgumentException – if sibling is not known to this file manager, or if the location is not known to this file manager and the file manager does not support unknown locations, or if relativeName is not valid
  • IOException – if an I/O error occurred, or if close has been called and this file manager cannot be reopened
  • IllegalStateException – if close has been called and this file manager cannot be reopened
Returns:a file object
/**
     * Returns a {@linkplain FileObject file object} for output
     * representing the specified <a href="JavaFileManager.html#relative_name">relative
     * name</a> in the specified package in the given location.
     *
     * <p>Optionally, this file manager might consider the sibling as
     * a hint for where to place the output.  The exact semantics of
     * this hint is unspecified.  The JDK compiler, javac, for
     * example, will place class files in the same directories as
     * originating source files unless a class file output directory
     * is provided.  To facilitate this behavior, javac might provide
     * the originating source file as sibling when calling this
     * method.
     *
     * <p>If the returned object represents a {@linkplain
     * JavaFileObject.Kind#SOURCE source} or {@linkplain
     * JavaFileObject.Kind#CLASS class} file, it must be an instance
     * of {@link JavaFileObject}.
     *
     * <p>Informally, the file object returned by this method is
     * located in the concatenation of the location, package name, and
     * relative name or next to the sibling argument.  See {@link
     * #getFileForInput getFileForInput} for an example.
     *
     * @param location a location
     * @param packageName a package name
     * @param relativeName a relative name
     * @param sibling a file object to be used as hint for placement;
     * might be {@code null}
     * @return a file object
     * @throws IllegalArgumentException if sibling is not known to
     * this file manager, or if the location is not known to this file
     * manager and the file manager does not support unknown
     * locations, or if {@code relativeName} is not valid
     * @throws IOException if an I/O error occurred, or if {@link
     * #close} has been called and this file manager cannot be
     * reopened
     * @throws IllegalStateException if {@link #close} has been called
     * and this file manager cannot be reopened
     */
    @Override
    public FileObject getFileForOutput(JavaFileManager.Location location,
            String packageName,
            String relativeName,
            FileObject sibling)
            throws IOException {
        throw new UnsupportedOperationException("getFileForOutput: location: " + location +
                ", packageName: " + packageName +
                ", relativeName: " + relativeName +
                ", sibling: " + sibling);
    }

    @Override
    public Location getLocationForModule(Location location, String moduleName) throws IOException {
        return stdFileManager.getLocationForModule(location, moduleName);
    }

    @Override
    public Location getLocationForModule(Location location, JavaFileObject fo) throws IOException {
        return stdFileManager.getLocationForModule(location, fo);
    }

    @Override
    public String inferModuleName(Location location) throws IOException {
        return stdFileManager.inferModuleName(location);
    }

    @Override
    public Iterable<Set<Location>> listLocationsForModules(Location location) throws IOException {
        return stdFileManager.listLocationsForModules(location);
    }

    @Override
    public boolean contains(Location location, FileObject file) throws IOException {
        return stdFileManager.contains(location, file);
    }

    
Flushes any resources opened for output by this file manager
directly or indirectly.  Flushing a closed file manager has no
effect.

Throws:
  • IOException – if an I/O error occurred
See Also:
/**
     * Flushes any resources opened for output by this file manager
     * directly or indirectly.  Flushing a closed file manager has no
     * effect.
     *
     * @throws IOException if an I/O error occurred
     * @see #close
     */
    @Override
    public void flush() throws IOException {
        // Nothing to flush
    }

    
Releases any resources opened by this file manager directly or
indirectly.  This might render this file manager useless and
the effect of subsequent calls to methods on this object or any
objects obtained through this object is undefined unless
explicitly allowed.  However, closing a file manager which has
already been closed has no effect.

Throws:
  • IOException – if an I/O error occurred
See Also:
/**
     * Releases any resources opened by this file manager directly or
     * indirectly.  This might render this file manager useless and
     * the effect of subsequent calls to methods on this object or any
     * objects obtained through this object is undefined unless
     * explicitly allowed.  However, closing a file manager which has
     * already been closed has no effect.
     *
     * @throws IOException if an I/O error occurred
     * @see #flush
     */
    @Override
    public void close() throws IOException {
        // Nothing to close
    }
}