001: /*
002: * Copyright 1994-2006 Sun Microsystems, Inc. All Rights Reserved.
003: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004: *
005: * This code is free software; you can redistribute it and/or modify it
006: * under the terms of the GNU General Public License version 2 only, as
007: * published by the Free Software Foundation. Sun designates this
008: * particular file as subject to the "Classpath" exception as provided
009: * by Sun in the LICENSE file that accompanied this code.
010: *
011: * This code is distributed in the hope that it will be useful, but WITHOUT
012: * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013: * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014: * version 2 for more details (a copy is included in the LICENSE file that
015: * accompanied this code).
016: *
017: * You should have received a copy of the GNU General Public License version
018: * 2 along with this work; if not, write to the Free Software Foundation,
019: * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020: *
021: * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022: * CA 95054 USA or visit www.sun.com if you need additional information or
023: * have any questions.
024: */
025:
026: package java.io;
027:
028: import java.io.InputStream;
029: import java.util.Enumeration;
030: import java.util.Vector;
031:
032: /**
033: * A <code>SequenceInputStream</code> represents
034: * the logical concatenation of other input
035: * streams. It starts out with an ordered
036: * collection of input streams and reads from
037: * the first one until end of file is reached,
038: * whereupon it reads from the second one,
039: * and so on, until end of file is reached
040: * on the last of the contained input streams.
041: *
042: * @author Author van Hoff
043: * @version 1.39, 05/05/07
044: * @since JDK1.0
045: */
046: public class SequenceInputStream extends InputStream {
047: Enumeration e;
048: InputStream in;
049:
050: /**
051: * Initializes a newly created <code>SequenceInputStream</code>
052: * by remembering the argument, which must
053: * be an <code>Enumeration</code> that produces
054: * objects whose run-time type is <code>InputStream</code>.
055: * The input streams that are produced by
056: * the enumeration will be read, in order,
057: * to provide the bytes to be read from this
058: * <code>SequenceInputStream</code>. After
059: * each input stream from the enumeration
060: * is exhausted, it is closed by calling its
061: * <code>close</code> method.
062: *
063: * @param e an enumeration of input streams.
064: * @see java.util.Enumeration
065: */
066: public SequenceInputStream(Enumeration<? extends InputStream> e) {
067: this .e = e;
068: try {
069: nextStream();
070: } catch (IOException ex) {
071: // This should never happen
072: throw new Error("panic");
073: }
074: }
075:
076: /**
077: * Initializes a newly
078: * created <code>SequenceInputStream</code>
079: * by remembering the two arguments, which
080: * will be read in order, first <code>s1</code>
081: * and then <code>s2</code>, to provide the
082: * bytes to be read from this <code>SequenceInputStream</code>.
083: *
084: * @param s1 the first input stream to read.
085: * @param s2 the second input stream to read.
086: */
087: public SequenceInputStream(InputStream s1, InputStream s2) {
088: Vector v = new Vector(2);
089:
090: v.addElement(s1);
091: v.addElement(s2);
092: e = v.elements();
093: try {
094: nextStream();
095: } catch (IOException ex) {
096: // This should never happen
097: throw new Error("panic");
098: }
099: }
100:
101: /**
102: * Continues reading in the next stream if an EOF is reached.
103: */
104: final void nextStream() throws IOException {
105: if (in != null) {
106: in.close();
107: }
108:
109: if (e.hasMoreElements()) {
110: in = (InputStream) e.nextElement();
111: if (in == null)
112: throw new NullPointerException();
113: } else
114: in = null;
115:
116: }
117:
118: /**
119: * Returns an estimate of the number of bytes that can be read (or
120: * skipped over) from the current underlying input stream without
121: * blocking by the next invocation of a method for the current
122: * underlying input stream. The next invocation might be
123: * the same thread or another thread. A single read or skip of this
124: * many bytes will not block, but may read or skip fewer bytes.
125: * <p>
126: * This method simply calls {@code available} of the current underlying
127: * input stream and returns the result.
128: *
129: * @return an estimate of the number of bytes that can be read (or
130: * skipped over) from the current underlying input stream
131: * without blocking or {@code 0} if this input stream
132: * has been closed by invoking its {@link #close()} method
133: * @exception IOException if an I/O error occurs.
134: *
135: * @since JDK1.1
136: */
137: public int available() throws IOException {
138: if (in == null) {
139: return 0; // no way to signal EOF from available()
140: }
141: return in.available();
142: }
143:
144: /**
145: * Reads the next byte of data from this input stream. The byte is
146: * returned as an <code>int</code> in the range <code>0</code> to
147: * <code>255</code>. If no byte is available because the end of the
148: * stream has been reached, the value <code>-1</code> is returned.
149: * This method blocks until input data is available, the end of the
150: * stream is detected, or an exception is thrown.
151: * <p>
152: * This method
153: * tries to read one character from the current substream. If it
154: * reaches the end of the stream, it calls the <code>close</code>
155: * method of the current substream and begins reading from the next
156: * substream.
157: *
158: * @return the next byte of data, or <code>-1</code> if the end of the
159: * stream is reached.
160: * @exception IOException if an I/O error occurs.
161: */
162: public int read() throws IOException {
163: if (in == null) {
164: return -1;
165: }
166: int c = in.read();
167: if (c == -1) {
168: nextStream();
169: return read();
170: }
171: return c;
172: }
173:
174: /**
175: * Reads up to <code>len</code> bytes of data from this input stream
176: * into an array of bytes. If <code>len</code> is not zero, the method
177: * blocks until at least 1 byte of input is available; otherwise, no
178: * bytes are read and <code>0</code> is returned.
179: * <p>
180: * The <code>read</code> method of <code>SequenceInputStream</code>
181: * tries to read the data from the current substream. If it fails to
182: * read any characters because the substream has reached the end of
183: * the stream, it calls the <code>close</code> method of the current
184: * substream and begins reading from the next substream.
185: *
186: * @param b the buffer into which the data is read.
187: * @param off the start offset in array <code>b</code>
188: * at which the data is written.
189: * @param len the maximum number of bytes read.
190: * @return int the number of bytes read.
191: * @exception NullPointerException If <code>b</code> is <code>null</code>.
192: * @exception IndexOutOfBoundsException If <code>off</code> is negative,
193: * <code>len</code> is negative, or <code>len</code> is greater than
194: * <code>b.length - off</code>
195: * @exception IOException if an I/O error occurs.
196: */
197: public int read(byte b[], int off, int len) throws IOException {
198: if (in == null) {
199: return -1;
200: } else if (b == null) {
201: throw new NullPointerException();
202: } else if (off < 0 || len < 0 || len > b.length - off) {
203: throw new IndexOutOfBoundsException();
204: } else if (len == 0) {
205: return 0;
206: }
207:
208: int n = in.read(b, off, len);
209: if (n <= 0) {
210: nextStream();
211: return read(b, off, len);
212: }
213: return n;
214: }
215:
216: /**
217: * Closes this input stream and releases any system resources
218: * associated with the stream.
219: * A closed <code>SequenceInputStream</code>
220: * cannot perform input operations and cannot
221: * be reopened.
222: * <p>
223: * If this stream was created
224: * from an enumeration, all remaining elements
225: * are requested from the enumeration and closed
226: * before the <code>close</code> method returns.
227: *
228: * @exception IOException if an I/O error occurs.
229: */
230: public void close() throws IOException {
231: do {
232: nextStream();
233: } while (in != null);
234: }
235: }
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