https://openjdk.java.net/ 
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 * Copyright (c) 1994, 2020, 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
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 */

package java.io;

import java.nio.channels.FileChannel;
import sun.nio.ch.FileChannelImpl;



A FileInputStream obtains input bytes from a file in a file system. What files are available depends on the host environment. 
FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader. 
Author: Arthur van Hoff
See Also:
API Note: To release resources used by this stream close should be called directly or by try-with-resources. Subclasses are responsible for the cleanup of resources acquired by the subclass. Subclasses that override Object.finalize in order to perform cleanup should be modified to use alternative cleanup mechanisms such as Cleaner and remove the overriding finalize method.
Implementation Requirements: If this FileInputStream has been subclassed and the close method has been overridden, the close method will be called when the FileInputStream is unreachable. Otherwise, it is implementation specific how the resource cleanup described in close is performed.
Since:  1.0
/**
 * A {@code FileInputStream} obtains input bytes
 * from a file in a file system. What files
 * are  available depends on the host environment.
 *
 * <p>{@code FileInputStream} is meant for reading streams of raw bytes
 * such as image data. For reading streams of characters, consider using
 * {@code FileReader}.
 *
 * @apiNote
 * To release resources used by this stream {@link #close} should be called
 * directly or by try-with-resources. Subclasses are responsible for the cleanup
 * of resources acquired by the subclass.
 * Subclasses that override {@link #finalize} in order to perform cleanup
 * should be modified to use alternative cleanup mechanisms such as
 * {@link java.lang.ref.Cleaner} and remove the overriding {@code finalize} method.
 *
 * @implSpec
 * If this FileInputStream has been subclassed and the {@link #close}
 * method has been overridden, the {@link #close} method will be
 * called when the FileInputStream is unreachable.
 * Otherwise, it is implementation specific how the resource cleanup described in
 * {@link #close} is performed.
 *
 * @author  Arthur van Hoff
 * @see     java.io.File
 * @see     java.io.FileDescriptor
 * @see     java.io.FileOutputStream
 * @see     java.nio.file.Files#newInputStream
 * @since   1.0
 */
public class FileInputStream extends InputStream
{
    /* File Descriptor - handle to the open file */
    private final FileDescriptor fd;

    
The path of the referenced file
(null if the stream is created with a file descriptor)

/**
     * The path of the referenced file
     * (null if the stream is created with a file descriptor)
     */
    private final String path;

    private volatile FileChannel channel;

    private final Object closeLock = new Object();

    private volatile boolean closed;

    
Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system. A new FileDescriptor object is created to represent this file connection. 
 First, if there is a security manager, its checkRead method is called with the name argument as its argument. 
 If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a FileNotFoundException is thrown. 
Params:
  • name –   the system-dependent file name.
Throws:
  • FileNotFoundException –  if the file does not exist,
            is a directory rather than a regular file,
            or for some other reason cannot be opened for
            reading.
  • SecurityException –  if a security manager exists and its checkRead method denies read access to the file.
See Also:
/**
     * Creates a {@code FileInputStream} by
     * opening a connection to an actual file,
     * the file named by the path name {@code name}
     * in the file system.  A new {@code FileDescriptor}
     * object is created to represent this file
     * connection.
     * <p>
     * First, if there is a security
     * manager, its {@code checkRead} method
     * is called with the {@code name} argument
     * as its argument.
     * <p>
     * If the named file does not exist, is a directory rather than a regular
     * file, or for some other reason cannot be opened for reading then a
     * {@code FileNotFoundException} is thrown.
     *
     * @param      name   the system-dependent file name.
     * @throws     FileNotFoundException  if the file does not exist,
     *             is a directory rather than a regular file,
     *             or for some other reason cannot be opened for
     *             reading.
     * @throws     SecurityException      if a security manager exists and its
     *             {@code checkRead} method denies read access
     *             to the file.
     * @see        java.lang.SecurityManager#checkRead(java.lang.String)
     */
    public FileInputStream(String name) throws FileNotFoundException {
        this(name != null ? new File(name) : null);
    }

    
Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system. A new FileDescriptor object is created to represent this file connection. 
 First, if there is a security manager, its checkRead method is called with the path represented by the file argument as its argument. 
 If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a FileNotFoundException is thrown. 
Params:
  • file –   the file to be opened for reading.
Throws:
  • FileNotFoundException –  if the file does not exist,
            is a directory rather than a regular file,
            or for some other reason cannot be opened for
            reading.
  • SecurityException –  if a security manager exists and its checkRead method denies read access to the file.
See Also:
/**
     * Creates a {@code FileInputStream} by
     * opening a connection to an actual file,
     * the file named by the {@code File}
     * object {@code file} in the file system.
     * A new {@code FileDescriptor} object
     * is created to represent this file connection.
     * <p>
     * First, if there is a security manager,
     * its {@code checkRead} method  is called
     * with the path represented by the {@code file}
     * argument as its argument.
     * <p>
     * If the named file does not exist, is a directory rather than a regular
     * file, or for some other reason cannot be opened for reading then a
     * {@code FileNotFoundException} is thrown.
     *
     * @param      file   the file to be opened for reading.
     * @throws     FileNotFoundException  if the file does not exist,
     *             is a directory rather than a regular file,
     *             or for some other reason cannot be opened for
     *             reading.
     * @throws     SecurityException      if a security manager exists and its
     *             {@code checkRead} method denies read access to the file.
     * @see        java.io.File#getPath()
     * @see        java.lang.SecurityManager#checkRead(java.lang.String)
     */
    public FileInputStream(File file) throws FileNotFoundException {
        String name = (file != null ? file.getPath() : null);
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(name);
        }
        if (name == null) {
            throw new NullPointerException();
        }
        if (file.isInvalid()) {
            throw new FileNotFoundException("Invalid file path");
        }
        fd = new FileDescriptor();
        fd.attach(this);
        path = name;
        open(name);
        FileCleanable.register(fd);       // open set the fd, register the cleanup
    }

    
Creates a FileInputStream by using the file descriptor fdObj, which represents an existing connection to an actual file in the file system. 
 If there is a security manager, its checkRead method is called with the file descriptor fdObj as its argument to see if it's ok to read the file descriptor. If read access is denied to the file descriptor a SecurityException is thrown. 
 If fdObj is null then a NullPointerException is thrown. 
 This constructor does not throw an exception if fdObj is invalid. However, if the methods are invoked on the resulting stream to attempt I/O on the stream, an IOException is thrown. 
Params:
  • fdObj –   the file descriptor to be opened for reading.
Throws:
  • SecurityException –  if a security manager exists and its checkRead method denies read access to the file descriptor.
See Also:
/**
     * Creates a {@code FileInputStream} by using the file descriptor
     * {@code fdObj}, which represents an existing connection to an
     * actual file in the file system.
     * <p>
     * If there is a security manager, its {@code checkRead} method is
     * called with the file descriptor {@code fdObj} as its argument to
     * see if it's ok to read the file descriptor. If read access is denied
     * to the file descriptor a {@code SecurityException} is thrown.
     * <p>
     * If {@code fdObj} is null then a {@code NullPointerException}
     * is thrown.
     * <p>
     * This constructor does not throw an exception if {@code fdObj}
     * is {@link java.io.FileDescriptor#valid() invalid}.
     * However, if the methods are invoked on the resulting stream to attempt
     * I/O on the stream, an {@code IOException} is thrown.
     *
     * @param      fdObj   the file descriptor to be opened for reading.
     * @throws     SecurityException      if a security manager exists and its
     *             {@code checkRead} method denies read access to the
     *             file descriptor.
     * @see        SecurityManager#checkRead(java.io.FileDescriptor)
     */
    public FileInputStream(FileDescriptor fdObj) {
        SecurityManager security = System.getSecurityManager();
        if (fdObj == null) {
            throw new NullPointerException();
        }
        if (security != null) {
            security.checkRead(fdObj);
        }
        fd = fdObj;
        path = null;

        /*
         * FileDescriptor is being shared by streams.
         * Register this stream with FileDescriptor tracker.
         */
        fd.attach(this);
    }

    
Opens the specified file for reading.

Params:
  • name – the name of the file
/**
     * Opens the specified file for reading.
     * @param name the name of the file
     */
    private native void open0(String name) throws FileNotFoundException;

    // wrap native call to allow instrumentation
    
Opens the specified file for reading.

Params:
  • name – the name of the file
/**
     * Opens the specified file for reading.
     * @param name the name of the file
     */
    private void open(String name) throws FileNotFoundException {
        open0(name);
    }

    
Reads a byte of data from this input stream. This method blocks
if no input is yet available.

Throws:
Returns: the next byte of data, or -1 if the end of the file is reached.
/**
     * Reads a byte of data from this input stream. This method blocks
     * if no input is yet available.
     *
     * @return     the next byte of data, or {@code -1} if the end of the
     *             file is reached.
     * @throws     IOException  if an I/O error occurs.
     */
    public int read() throws IOException {
        return read0();
    }

    private native int read0() throws IOException;

    
Reads a subarray as a sequence of bytes.

Params:
  • b – the data to be written
  • off – the start offset in the data
  • len – the number of bytes that are written
Throws:
/**
     * Reads a subarray as a sequence of bytes.
     * @param     b the data to be written
     * @param     off the start offset in the data
     * @param     len the number of bytes that are written
     * @throws    IOException If an I/O error has occurred.
     */
    private native int readBytes(byte b[], int off, int len) throws IOException;

    
Reads up to b.length bytes of data from this input stream into an array of bytes. This method blocks until some input is available. 
Params:
  • b –   the buffer into which the data is read.
Throws:
Returns: the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.
/**
     * Reads up to {@code b.length} bytes of data from this input
     * stream into an array of bytes. This method blocks until some input
     * is available.
     *
     * @param      b   the buffer into which the data is read.
     * @return     the total number of bytes read into the buffer, or
     *             {@code -1} if there is no more data because the end of
     *             the file has been reached.
     * @throws     IOException  if an I/O error occurs.
     */
    public int read(byte b[]) throws IOException {
        return readBytes(b, 0, b.length);
    }

    
Reads up to len bytes of data from this input stream into an array of bytes. If len is not zero, the method blocks until some input is available; otherwise, no bytes are read and 0 is returned. 
Params:
  • b –     the buffer into which the data is read.
  • off –  the start offset in the destination array b
  • len –   the maximum number of bytes read.
Throws:
Returns: the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.
/**
     * Reads up to {@code len} bytes of data from this input stream
     * into an array of bytes. If {@code len} is not zero, the method
     * blocks until some input is available; otherwise, no
     * bytes are read and {@code 0} is returned.
     *
     * @param      b     the buffer into which the data is read.
     * @param      off   the start offset in the destination array {@code b}
     * @param      len   the maximum number of bytes read.
     * @return     the total number of bytes read into the buffer, or
     *             {@code -1} if there is no more data because the end of
     *             the file has been reached.
     * @throws     NullPointerException If {@code b} is {@code null}.
     * @throws     IndexOutOfBoundsException If {@code off} is negative,
     *             {@code len} is negative, or {@code len} is greater than
     *             {@code b.length - off}
     * @throws     IOException  if an I/O error occurs.
     */
    public int read(byte b[], int off, int len) throws IOException {
        return readBytes(b, off, len);
    }

    
Skips over and discards n bytes of data from the input stream. 
The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. If n is negative, the method will try to skip backwards. In case the backing file does not support backward skip at its current position, an IOException is thrown. The actual number of bytes skipped is returned. If it skips forwards, it returns a positive value. If it skips backwards, it returns a negative value. 
This method may skip more bytes than what are remaining in the
backing file. This produces no exception and the number of bytes skipped
may include some number of bytes that were beyond the EOF of the
backing file. Attempting to read from the stream after skipping past
the end will result in -1 indicating the end of the file.

Params:
  • n –   the number of bytes to be skipped.
Throws:
  • IOException –  if n is negative, if the stream does not
            support seek, or if an I/O error occurs.
Returns:    the actual number of bytes skipped.
/**
     * Skips over and discards {@code n} bytes of data from the
     * input stream.
     *
     * <p>The {@code skip} method may, for a variety of
     * reasons, end up skipping over some smaller number of bytes,
     * possibly {@code 0}. If {@code n} is negative, the method
     * will try to skip backwards. In case the backing file does not support
     * backward skip at its current position, an {@code IOException} is
     * thrown. The actual number of bytes skipped is returned. If it skips
     * forwards, it returns a positive value. If it skips backwards, it
     * returns a negative value.
     *
     * <p>This method may skip more bytes than what are remaining in the
     * backing file. This produces no exception and the number of bytes skipped
     * may include some number of bytes that were beyond the EOF of the
     * backing file. Attempting to read from the stream after skipping past
     * the end will result in -1 indicating the end of the file.
     *
     * @param      n   the number of bytes to be skipped.
     * @return     the actual number of bytes skipped.
     * @throws     IOException  if n is negative, if the stream does not
     *             support seek, or if an I/O error occurs.
     */
    public long skip(long n) throws IOException {
        return skip0(n);
    }

    private native long skip0(long n) throws IOException;

    
Returns an estimate of the number of remaining bytes that can be read (or
skipped over) from this input stream without blocking by the next
invocation of a method for this input stream. Returns 0 when the file
position is beyond EOF. The next invocation might be the same thread
or another thread. A single read or skip of this many bytes will not
block, but may read or skip fewer bytes.

 In some cases, a non-blocking read (or skip) may appear to be
blocked when it is merely slow, for example when reading large
files over slow networks.

Throws:
  • IOException –  if this file input stream has been closed by calling close or an I/O error occurs.
Returns:    an estimate of the number of remaining bytes that can be read
            (or skipped over) from this input stream without blocking.
/**
     * Returns an estimate of the number of remaining bytes that can be read (or
     * skipped over) from this input stream without blocking by the next
     * invocation of a method for this input stream. Returns 0 when the file
     * position is beyond EOF. The next invocation might be the same thread
     * or another thread. A single read or skip of this many bytes will not
     * block, but may read or skip fewer bytes.
     *
     * <p> In some cases, a non-blocking read (or skip) may appear to be
     * blocked when it is merely slow, for example when reading large
     * files over slow networks.
     *
     * @return     an estimate of the number of remaining bytes that can be read
     *             (or skipped over) from this input stream without blocking.
     * @throws     IOException  if this file input stream has been closed by calling
     *             {@code close} or an I/O error occurs.
     */
    public int available() throws IOException {
        return available0();
    }

    private native int available0() throws IOException;

    
Closes this file input stream and releases any system resources
associated with the stream.

 If this stream has an associated channel then the channel is closed
as well.

Throws:
API Note: Overriding close to perform cleanup actions is reliable only when called directly or when called by try-with-resources. Do not depend on finalization to invoke close; finalization is not reliable and is deprecated. If cleanup of native resources is needed, other mechanisms such as Cleaner should be used.
@revised1.4
/**
     * Closes this file input stream and releases any system resources
     * associated with the stream.
     *
     * <p> If this stream has an associated channel then the channel is closed
     * as well.
     *
     * @apiNote
     * Overriding {@link #close} to perform cleanup actions is reliable
     * only when called directly or when called by try-with-resources.
     * Do not depend on finalization to invoke {@code close};
     * finalization is not reliable and is deprecated.
     * If cleanup of native resources is needed, other mechanisms such as
     * {@linkplain java.lang.ref.Cleaner} should be used.
     *
     * @throws     IOException  if an I/O error occurs.
     *
     * @revised 1.4
     */
    public void close() throws IOException {
        if (closed) {
            return;
        }
        synchronized (closeLock) {
            if (closed) {
                return;
            }
            closed = true;
        }

        FileChannel fc = channel;
        if (fc != null) {
            // possible race with getChannel(), benign since
            // FileChannel.close is final and idempotent
            fc.close();
        }

        fd.closeAll(new Closeable() {
            public void close() throws IOException {
               fd.close();
           }
        });
    }

    
Returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream. 
Throws:
See Also:
Returns:    the file descriptor object associated with this stream.
/**
     * Returns the {@code FileDescriptor}
     * object  that represents the connection to
     * the actual file in the file system being
     * used by this {@code FileInputStream}.
     *
     * @return     the file descriptor object associated with this stream.
     * @throws     IOException  if an I/O error occurs.
     * @see        java.io.FileDescriptor
     */
    public final FileDescriptor getFD() throws IOException {
        if (fd != null) {
            return fd;
        }
        throw new IOException();
    }

    
Returns the unique FileChannel object associated with this file input stream. 
 The initial 
position of the returned channel will be equal to the number of bytes read from the file so far. Reading bytes from this stream will increment the channel's position. Changing the channel's position, either explicitly or by reading, will change this stream's file position. 
Returns: the file channel associated with this file input stream
Since:1.4
/**
     * Returns the unique {@link java.nio.channels.FileChannel FileChannel}
     * object associated with this file input stream.
     *
     * <p> The initial {@link java.nio.channels.FileChannel#position()
     * position} of the returned channel will be equal to the
     * number of bytes read from the file so far.  Reading bytes from this
     * stream will increment the channel's position.  Changing the channel's
     * position, either explicitly or by reading, will change this stream's
     * file position.
     *
     * @return  the file channel associated with this file input stream
     *
     * @since 1.4
     */
    public FileChannel getChannel() {
        FileChannel fc = this.channel;
        if (fc == null) {
            synchronized (this) {
                fc = this.channel;
                if (fc == null) {
                    this.channel = fc = FileChannelImpl.open(fd, path, true,
                        false, false, this);
                    if (closed) {
                        try {
                            // possible race with close(), benign since
                            // FileChannel.close is final and idempotent
                            fc.close();
                        } catch (IOException ioe) {
                            throw new InternalError(ioe); // should not happen
                        }
                    }
                }
            }
        }
        return fc;
    }

    private static native void initIDs();

    static {
        initIDs();
    }
}