Java tutorial
/* * Copyright (c) 1994, 2018, 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 <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) */ private final String path; private volatile FileChannel channel; private final Object closeLock = new Object(); private volatile boolean closed; /** * 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 <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); FileCleanable.register(fd); // open set the fd, register the cleanup } /** * 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; /* * FileDescriptor is being shared by streams. * Register this stream with FileDescriptor tracker. */ fd.attach(this); } /** * 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. * @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. * * @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. * @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 <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 <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 <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. * * <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. * * <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 <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 {@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(); } }