Java tutorial
/* * 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; /** * This class is the superclass of all classes that filter output * streams. These streams sit on top of an already existing output * stream (the <i>underlying</i> output stream) which it uses as its * basic sink of data, but possibly transforming the data along the * way or providing additional functionality. * <p> * The class <code>FilterOutputStream</code> itself simply overrides * all methods of <code>OutputStream</code> with versions that pass * all requests to the underlying output stream. Subclasses of * <code>FilterOutputStream</code> may further override some of these * methods as well as provide additional methods and fields. * * @author Jonathan Payne * @since 1.0 */ public class FilterOutputStream extends OutputStream { /** * The underlying output stream to be filtered. */ protected OutputStream out; /** * Whether the stream is closed; implicitly initialized to false. */ private volatile boolean closed; /** * Object used to prevent a race on the 'closed' instance variable. */ private final Object closeLock = new Object(); /** * Creates an output stream filter built on top of the specified * underlying output stream. * * @param out the underlying output stream to be assigned to * the field {@code this.out} for later use, or * <code>null</code> if this instance is to be * created without an underlying stream. */ public FilterOutputStream(OutputStream out) { this.out = out; } /** * Writes the specified <code>byte</code> to this output stream. * <p> * The <code>write</code> method of <code>FilterOutputStream</code> * calls the <code>write</code> method of its underlying output stream, * that is, it performs {@code out.write(b)}. * <p> * Implements the abstract {@code write} method of {@code OutputStream}. * * @param b the <code>byte</code>. * @exception IOException if an I/O error occurs. */ @Override public void write(int b) throws IOException { out.write(b); } /** * Writes <code>b.length</code> bytes to this output stream. * <p> * The <code>write</code> method of <code>FilterOutputStream</code> * calls its <code>write</code> method of three arguments with the * arguments <code>b</code>, <code>0</code>, and * <code>b.length</code>. * <p> * Note that this method does not call the one-argument * <code>write</code> method of its underlying output stream with * the single argument <code>b</code>. * * @param b the data to be written. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#write(byte[], int, int) */ @Override public void write(byte b[]) throws IOException { write(b, 0, b.length); } /** * Writes <code>len</code> bytes from the specified * <code>byte</code> array starting at offset <code>off</code> to * this output stream. * <p> * The <code>write</code> method of <code>FilterOutputStream</code> * calls the <code>write</code> method of one argument on each * <code>byte</code> to output. * <p> * Note that this method does not call the <code>write</code> method * of its underlying output stream with the same arguments. Subclasses * of <code>FilterOutputStream</code> should provide a more efficient * implementation of this method. * * @param b the data. * @param off the start offset in the data. * @param len the number of bytes to write. * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#write(int) */ @Override public void write(byte b[], int off, int len) throws IOException { if ((off | len | (b.length - (len + off)) | (off + len)) < 0) throw new IndexOutOfBoundsException(); for (int i = 0; i < len; i++) { write(b[off + i]); } } /** * Flushes this output stream and forces any buffered output bytes * to be written out to the stream. * <p> * The <code>flush</code> method of <code>FilterOutputStream</code> * calls the <code>flush</code> method of its underlying output stream. * * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#out */ @Override public void flush() throws IOException { out.flush(); } /** * Closes this output stream and releases any system resources * associated with the stream. * <p> * When not already closed, the {@code close} method of {@code * FilterOutputStream} calls its {@code flush} method, and then * calls the {@code close} method of its underlying output stream. * * @exception IOException if an I/O error occurs. * @see java.io.FilterOutputStream#flush() * @see java.io.FilterOutputStream#out */ @Override public void close() throws IOException { if (closed) { return; } synchronized (closeLock) { if (closed) { return; } closed = true; } Throwable flushException = null; try { flush(); } catch (Throwable e) { flushException = e; throw e; } finally { if (flushException == null) { out.close(); } else { try { out.close(); } catch (Throwable closeException) { // evaluate possible precedence of flushException over closeException if ((flushException instanceof ThreadDeath) && !(closeException instanceof ThreadDeath)) { flushException.addSuppressed(closeException); throw (ThreadDeath) flushException; } if (flushException != closeException) { closeException.addSuppressed(flushException); } throw closeException; } } } } }