Java tutorial
/* * Copyright (c) 1994, 2011, 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.io.InputStream; import java.util.Enumeration; import java.util.Vector; /** * A <code>SequenceInputStream</code> represents * the logical concatenation of other input * streams. It starts out with an ordered * collection of input streams and reads from * the first one until end of file is reached, * whereupon it reads from the second one, * and so on, until end of file is reached * on the last of the contained input streams. * * @author Author van Hoff * @since 1.0 */ public class SequenceInputStream extends InputStream { Enumeration<? extends InputStream> e; InputStream in; /** * Initializes a newly created <code>SequenceInputStream</code> * by remembering the argument, which must * be an <code>Enumeration</code> that produces * objects whose run-time type is <code>InputStream</code>. * The input streams that are produced by * the enumeration will be read, in order, * to provide the bytes to be read from this * <code>SequenceInputStream</code>. After * each input stream from the enumeration * is exhausted, it is closed by calling its * <code>close</code> method. * * @param e an enumeration of input streams. * @see java.util.Enumeration */ public SequenceInputStream(Enumeration<? extends InputStream> e) { this.e = e; peekNextStream(); } /** * Initializes a newly * created <code>SequenceInputStream</code> * by remembering the two arguments, which * will be read in order, first <code>s1</code> * and then <code>s2</code>, to provide the * bytes to be read from this <code>SequenceInputStream</code>. * * @param s1 the first input stream to read. * @param s2 the second input stream to read. */ public SequenceInputStream(InputStream s1, InputStream s2) { Vector<InputStream> v = new Vector<>(2); v.addElement(s1); v.addElement(s2); e = v.elements(); peekNextStream(); } /** * Continues reading in the next stream if an EOF is reached. */ final void nextStream() throws IOException { if (in != null) { in.close(); } peekNextStream(); } private void peekNextStream() { if (e.hasMoreElements()) { in = (InputStream) e.nextElement(); if (in == null) throw new NullPointerException(); } else { in = null; } } /** * Returns an estimate of the number of bytes that can be read (or * skipped over) from the current underlying input stream without * blocking by the next invocation of a method for the current * underlying input stream. 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> * This method simply calls {@code available} of the current underlying * input stream and returns the result. * * @return an estimate of the number of bytes that can be read (or * skipped over) from the current underlying input stream * without blocking or {@code 0} if this input stream * has been closed by invoking its {@link #close()} method * @exception IOException if an I/O error occurs. * * @since 1.1 */ public int available() throws IOException { if (in == null) { return 0; // no way to signal EOF from available() } return in.available(); } /** * Reads the next byte of data from this input stream. The 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 * tries to read one character from the current substream. If it * reaches the end of the stream, it calls the <code>close</code> * method of the current substream and begins reading from the next * substream. * * @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. */ public int read() throws IOException { while (in != null) { int c = in.read(); if (c != -1) { return c; } nextStream(); } return -1; } /** * 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 at least 1 byte of input is available; otherwise, no * bytes are read and <code>0</code> is returned. * <p> * The <code>read</code> method of <code>SequenceInputStream</code> * tries to read the data from the current substream. If it fails to * read any characters because the substream has reached the end of * the stream, it calls the <code>close</code> method of the current * substream and begins reading from the next substream. * * @param b the buffer into which the data is read. * @param off the start offset in array <code>b</code> * at which the data is written. * @param len the maximum number of bytes read. * @return int the number of bytes read. * @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 { if (in == null) { return -1; } else if (b == null) { throw new NullPointerException(); } else if (off < 0 || len < 0 || len > b.length - off) { throw new IndexOutOfBoundsException(); } else if (len == 0) { return 0; } do { int n = in.read(b, off, len); if (n > 0) { return n; } nextStream(); } while (in != null); return -1; } /** * Closes this input stream and releases any system resources * associated with the stream. * A closed <code>SequenceInputStream</code> * cannot perform input operations and cannot * be reopened. * <p> * If this stream was created * from an enumeration, all remaining elements * are requested from the enumeration and closed * before the <code>close</code> method returns. * * @exception IOException if an I/O error occurs. */ public void close() throws IOException { do { nextStream(); } while (in != null); } }