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; /** * A <code>FilterInputStream</code> contains * some other input stream, which it uses as * its basic source of data, possibly transforming * the data along the way or providing additional * functionality. The class <code>FilterInputStream</code> * itself simply overrides all methods of * <code>InputStream</code> with versions that * pass all requests to the contained input * stream. Subclasses of <code>FilterInputStream</code> * may further override some of these methods * and may also provide additional methods * and fields. * * @author Jonathan Payne * @since 1.0 */ public class FilterInputStream extends InputStream { /** * The input stream to be filtered. */ protected volatile InputStream in; /** * Creates a <code>FilterInputStream</code> * by assigning the argument <code>in</code> * to the field <code>this.in</code> so as * to remember it for later use. * * @param in the underlying input stream, or <code>null</code> if * this instance is to be created without an underlying stream. */ protected FilterInputStream(InputStream in) { this.in = in; } /** * Reads the next byte of data from this input stream. The value * byte is returned as an <code>int</code> in the range * <code>0</code> to <code>255</code>. If no byte is available * because the end of the stream has been reached, the value * <code>-1</code> is returned. This method blocks until input data * is available, the end of the stream is detected, or an exception * is thrown. * <p> * This method * simply performs <code>in.read()</code> and returns the result. * * @return the next byte of data, or <code>-1</code> if the end of the * stream is reached. * @exception IOException if an I/O error occurs. * @see java.io.FilterInputStream#in */ public int read() throws IOException { return in.read(); } /** * 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. * <p> * This method simply performs the call * <code>read(b, 0, b.length)</code> and returns * the result. It is important that it does * <i>not</i> do <code>in.read(b)</code> instead; * certain subclasses of <code>FilterInputStream</code> * depend on the implementation strategy actually * used. * * @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 stream has been reached. * @exception IOException if an I/O error occurs. * @see java.io.FilterInputStream#read(byte[], int, int) */ public int read(byte b[]) throws IOException { return read(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. * <p> * This method simply performs <code>in.read(b, off, len)</code> * and returns the result. * * @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 stream 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. * @see java.io.FilterInputStream#in */ public int read(byte b[], int off, int len) throws IOException { return in.read(b, off, len); } /** * Skips over and discards <code>n</code> bytes of data from the * input stream. The <code>skip</code> method may, for a variety of * reasons, end up skipping over some smaller number of bytes, * possibly <code>0</code>. The actual number of bytes skipped is * returned. * <p> * This method simply performs <code>in.skip(n)</code>. * * @param n the number of bytes to be skipped. * @return the actual number of bytes skipped. * @throws IOException if {@code in.skip(n)} throws an IOException. */ public long skip(long n) throws IOException { return in.skip(n); } /** * Returns an estimate of the number of bytes that can be read (or * skipped over) from this input stream without blocking by the next * caller of a method for this input stream. The next caller 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> * This method returns the result of {@link #in in}.available(). * * @return an estimate of the number of bytes that can be read (or skipped * over) from this input stream without blocking. * @exception IOException if an I/O error occurs. */ public int available() throws IOException { return in.available(); } /** * Closes this input stream and releases any system resources * associated with the stream. * This * method simply performs <code>in.close()</code>. * * @exception IOException if an I/O error occurs. * @see java.io.FilterInputStream#in */ public void close() throws IOException { in.close(); } /** * Marks the current position in this input stream. A subsequent * call to the <code>reset</code> method repositions this stream at * the last marked position so that subsequent reads re-read the same bytes. * <p> * The <code>readlimit</code> argument tells this input stream to * allow that many bytes to be read before the mark position gets * invalidated. * <p> * This method simply performs <code>in.mark(readlimit)</code>. * * @param readlimit the maximum limit of bytes that can be read before * the mark position becomes invalid. * @see java.io.FilterInputStream#in * @see java.io.FilterInputStream#reset() */ public synchronized void mark(int readlimit) { in.mark(readlimit); } /** * Repositions this stream to the position at the time the * <code>mark</code> method was last called on this input stream. * <p> * This method * simply performs <code>in.reset()</code>. * <p> * Stream marks are intended to be used in * situations where you need to read ahead a little to see what's in * the stream. Often this is most easily done by invoking some * general parser. If the stream is of the type handled by the * parse, it just chugs along happily. If the stream is not of * that type, the parser should toss an exception when it fails. * If this happens within readlimit bytes, it allows the outer * code to reset the stream and try another parser. * * @exception IOException if the stream has not been marked or if the * mark has been invalidated. * @see java.io.FilterInputStream#in * @see java.io.FilterInputStream#mark(int) */ public synchronized void reset() throws IOException { in.reset(); } /** * Tests if this input stream supports the <code>mark</code> * and <code>reset</code> methods. * This method * simply performs <code>in.markSupported()</code>. * * @return <code>true</code> if this stream type supports the * <code>mark</code> and <code>reset</code> method; * <code>false</code> otherwise. * @see java.io.FilterInputStream#in * @see java.io.InputStream#mark(int) * @see java.io.InputStream#reset() */ public boolean markSupported() { return in.markSupported(); } }