https://openjdk.java.net/ 
/*
 * Copyright (c) 1994, 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.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 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</code> obtains input bytes
 * from a file in a file system. What files
 * are  available depends on the host environment.
 *
 * <p><code>FileInputStream</code> is meant for reading streams of raw bytes
 * such as image data. For reading streams of characters, consider using
 * <code>FileReader</code>.
 *
 * @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;

    private final Object altFinalizer;

    
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</code> by
     * opening a connection to an actual file,
     * the file named by the path name <code>name</code>
     * in the file system.  A new <code>FileDescriptor</code>
     * object is created to represent this file
     * connection.
     * <p>
     * First, if there is a security
     * manager, its <code>checkRead</code> method
     * is called with the <code>name</code> 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</code> is thrown.
     *
     * @param      name   the system-dependent file name.
     * @exception  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.
     * @exception  SecurityException      if a security manager exists and its
     *               <code>checkRead</code> 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</code> by
     * opening a connection to an actual file,
     * the file named by the <code>File</code>
     * object <code>file</code> in the file system.
     * A new <code>FileDescriptor</code> object
     * is created to represent this file connection.
     * <p>
     * First, if there is a security manager,
     * its <code>checkRead</code> method  is called
     * with the path represented by the <code>file</code>
     * 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</code> is thrown.
     *
     * @param      file   the file to be opened for reading.
     * @exception  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.
     * @exception  SecurityException      if a security manager exists and its
     *               <code>checkRead</code> 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);
        altFinalizer = getFinalizer(this);
        if (altFinalizer == null) {
            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</code> by using the file descriptor
     * <code>fdObj</code>, which represents an existing connection to an
     * actual file in the file system.
     * <p>
     * If there is a security manager, its <code>checkRead</code> method is
     * called with the file descriptor <code>fdObj</code> 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</code> is thrown.
     * <p>
     * If <code>fdObj</code> is null then a <code>NullPointerException</code>
     * is thrown.
     * <p>
     * This constructor does not throw an exception if <code>fdObj</code>
     * 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</code> is thrown.
     *
     * @param      fdObj   the file descriptor to be opened for reading.
     * @throws     SecurityException      if a security manager exists and its
     *                 <code>checkRead</code> 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;
        altFinalizer = 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</code> if the end of the
     *             file is reached.
     * @exception  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
     * @exception 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</code> 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</code> if there is no more data because the end of
     *             the file has been reached.
     * @exception  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</code> bytes of data from this input stream
     * into an array of bytes. If <code>len</code> is not zero, the method
     * blocks until some input is available; otherwise, no
     * bytes are read and <code>0</code> is returned.
     *
     * @param      b     the buffer into which the data is read.
     * @param      off   the start offset in the destination array <code>b</code>
     * @param      len   the maximum number of bytes read.
     * @return     the total number of bytes read into the buffer, or
     *             <code>-1</code> if there is no more data because the end of
     *             the file has been reached.
     * @exception  NullPointerException If <code>b</code> is <code>null</code>.
     * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
     * <code>len</code> is negative, or <code>len</code> is greater than
     * <code>b.length - off</code>
     * @exception  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</code> bytes of data from the
     * input stream.
     *
     * <p>The <code>skip</code> method may, for a variety of
     * reasons, end up skipping over some smaller number of bytes,
     * possibly <code>0</code>. If <code>n</code> 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</code> 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.
     * @exception  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.
     * @exception  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
@specJSR-51
/**
     * 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.
     *
     * @exception  IOException  if an I/O error occurs.
     *
     * @revised 1.4
     * @spec JSR-51
     */
    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</code>
     * object  that represents the connection to
     * the actual file in the file system being
     * used by this <code>FileInputStream</code>.
     *
     * @return     the file descriptor object associated with this stream.
     * @exception  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
@specJSR-51
/**
     * 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
     * @spec JSR-51
     */
    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();
    }

    
Ensures that the close method of this file input stream is called when there are no more references to it. The finalize method does not call close directly. 
Throws:
See Also:
API Note: To release resources used by this stream close should be called directly or by try-with-resources.
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.
Deprecated:The finalize method has been deprecated and will be removed. Subclasses that override finalize in order to perform cleanup should be modified to use alternative cleanup mechanisms and to remove the overriding finalize method. When overriding the finalize method, its implementation must explicitly ensure that super.finalize() is invoked as described in Object.finalize. See the specification for Object.finalize() for further information about migration options.
/**
     * Ensures that the {@link #close} method of this file input stream is
     * called when there are no more references to it.
     * The {@link #finalize} method does not call {@link #close} directly.
     *
     * @apiNote
     * To release resources used by this stream {@link #close} should be called
     * directly or by try-with-resources.
     *
     * @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.
     *
     * @deprecated The {@code finalize} method has been deprecated and will be removed.
     *     Subclasses that override {@code finalize} in order to perform cleanup
     *     should be modified to use alternative cleanup mechanisms and
     *     to remove the overriding {@code finalize} method.
     *     When overriding the {@code finalize} method, its implementation must explicitly
     *     ensure that {@code super.finalize()} is invoked as described in {@link Object#finalize}.
     *     See the specification for {@link Object#finalize()} for further
     *     information about migration options.
     *
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FileInputStream#close()
     */
    @Deprecated(since="9", forRemoval = true)
    protected void finalize() throws IOException {
    }

    /*
     * Returns a finalizer object if the FIS needs a finalizer; otherwise null.
     * If the FIS has a close method; it needs an AltFinalizer.
     */
    private static Object getFinalizer(FileInputStream fis) {
        Class<?> clazz = fis.getClass();
        while (clazz != FileInputStream.class) {
            try {
                clazz.getDeclaredMethod("close");
                return new AltFinalizer(fis);
            } catch (NoSuchMethodException nsme) {
                // ignore
            }
            clazz = clazz.getSuperclass();
        }
        return null;
    }
    
Class to call FileInputStream.close when finalized. If finalization of the stream is needed, an instance is created in its constructor(s). When the set of instances related to the stream is unreachable, the AltFinalizer performs the needed call to the stream's close method. 
/**
     * Class to call {@code FileInputStream.close} when finalized.
     * If finalization of the stream is needed, an instance is created
     * in its constructor(s).  When the set of instances
     * related to the stream is unreachable, the AltFinalizer performs
     * the needed call to the stream's {@code close} method.
     */
    static class AltFinalizer {
        private final FileInputStream fis;

        AltFinalizer(FileInputStream fis) {
            this.fis = fis;
        }

        @Override
        @SuppressWarnings("deprecation")
        protected final void finalize() {
            try {
                if ((fis.fd != null) && (fis.fd != FileDescriptor.in)) {
                    /* if fd is shared, the references in FileDescriptor
                     * will ensure that finalizer is only called when
                     * safe to do so. All references using the fd have
                     * become unreachable. We can call close()
                     */
                    fis.close();
                }
            } catch (IOException ioe) {
                // ignore
            }
        }
    }
}