- 001
/* - 002
* @(#)FileDescriptor.java 1.4 05/11/17 - 003 *
- 004 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
- 005 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
- 006
*/ - 007
- 008package java.io;
- 009
- 010/**
- 011 * Instances of the file descriptor class serve as an opaque handle
- 012 * to the underlying machine-specific structure representing an open
- 013 * file, an open socket, or another source or sink of bytes. The
- 014 * main practical use for a file descriptor is to create a
- 015 * <code>FileInputStream</code> or <code>FileOutputStream</code> to
- 016 * contain it.
- 017 * <p>
- 018 * Applications should not create their own file descriptors.
- 019 *
- 020 * @author Pavani Diwanji
- 021 * @version 1.4, 11/17/05
- 022 * @see java.io.FileInputStream
- 023 * @see java.io.FileOutputStream
- 024 * @since JDK1.0
- 025 */
- 026public final class FileDescriptor {
- 027
- 028 private int fd;
- 029
- 030 private long handle;
- 031
- 032 /**
- 033 * Constructs an (invalid) FileDescriptor
- 034 * object.
- 035 */
- 036 public /**/FileDescriptor() {
- 037 fd = -1;
- 038 handle = -1;
- 039 }
- 040
- 041 private /* */FileDescriptor(int fd) {
- 042 this.fd = fd;
- 043 handle = -1;
- 044 }
- 045
- 046 static {
- 047 initIDs();
- 048 }
- 049
- 050 /**
- 051 * A handle to the standard input stream. Usually, this file
- 052 * descriptor is not used directly, but rather via the input stream
- 053 * known as <code>System.in</code>.
- 054 *
- 055 * @see java.lang.System#in
- 056 */
- 057 public static final FileDescriptor in = standardStream(0);
- 058
- 059 /**
- 060 * A handle to the standard output stream. Usually, this file
- 061 * descriptor is not used directly, but rather via the output stream
- 062 * known as <code>System.out</code>.
- 063 * @see java.lang.System#out
- 064 */
- 065 public static final FileDescriptor out = standardStream(1);
- 066
- 067 /**
- 068 * A handle to the standard error stream. Usually, this file
- 069 * descriptor is not used directly, but rather via the output stream
- 070 * known as <code>System.err</code>.
- 071 *
- 072 * @see java.lang.System#err
- 073 */
- 074 public static final FileDescriptor err = standardStream(2);
- 075
- 076 /**
- 077 * Tests if this file descriptor object is valid.
- 078 *
- 079 * @return <code>true</code> if the file descriptor object represents a
- 080 * valid, open file, socket, or other active I/O connection;
- 081 * <code>false</code> otherwise.
- 082 */
- 083 public boolean valid() {
- 084 return ((handle != -1) || (fd != -1));
- 085 }
- 086
- 087 /**
- 088 * Force all system buffers to synchronize with the underlying
- 089 * device. This method returns after all modified data and
- 090 * attributes of this FileDescriptor have been written to the
- 091 * relevant device(s). In particular, if this FileDescriptor
- 092 * refers to a physical storage medium, such as a file in a file
- 093 * system, sync will not return until all in-memory modified copies
- 094 * of buffers associated with this FileDesecriptor have been
- 095 * written to the physical medium.
- 096 *
- 097 * sync is meant to be used by code that requires physical
- 098 * storage (such as a file) to be in a known state For
- 099 * example, a class that provided a simple transaction facility
- 100 * might use sync to ensure that all changes to a file caused
- 101 * by a given transaction were recorded on a storage medium.
- 102 *
- 103 * sync only affects buffers downstream of this FileDescriptor. If
- 104 * any in-memory buffering is being done by the application (for
- 105 * example, by a BufferedOutputStream object), those buffers must
- 106 * be flushed into the FileDescriptor (for example, by invoking
- 107 * OutputStream.flush) before that data will be affected by sync.
- 108 *
- 109 * @exception SyncFailedException
- 110 * Thrown when the buffers cannot be flushed,
- 111 * or because the system cannot guarantee that all the
- 112 * buffers have been synchronized with physical media.
- 113 * @since JDK1.1
- 114 */
- 115 public native void sync() throws SyncFailedException;
- 116
- 117 /* This routine initializes JNI field offsets for the class */
- 118 private static native void initIDs();
- 119
- 120 private static native long set(int d);
- 121
- 122 private static FileDescriptor standardStream(int fd) {
- 123 FileDescriptor desc = new FileDescriptor();
- 124 desc.handle = set(fd);
- 125 return desc;
- 126 }
- 127
- 128}
