1 /*
2 * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.io;
27
28 import java.io.InputStream;
29 import java.util.Enumeration;
30 import java.util.Vector;
31
32 /**
33 * A <code>SequenceInputStream</code> represents
34 * the logical concatenation of other input
35 * streams. It starts out with an ordered
36 * collection of input streams and reads from
37 * the first one until end of file is reached,
38 * whereupon it reads from the second one,
39 * and so on, until end of file is reached
40 * on the last of the contained input streams.
41 *
42 * @author Author van Hoff
43 * @since 1.0
44 */
45 public
46 class SequenceInputStream extends InputStream {
47 Enumeration<? extends InputStream> e;
48 InputStream in;
49
50 /**
51 * Initializes a newly created <code>SequenceInputStream</code>
52 * by remembering the argument, which must
53 * be an <code>Enumeration</code> that produces
54 * objects whose run-time type is <code>InputStream</code>.
55 * The input streams that are produced by
56 * the enumeration will be read, in order,
57 * to provide the bytes to be read from this
58 * <code>SequenceInputStream</code>. After
59 * each input stream from the enumeration
60 * is exhausted, it is closed by calling its
61 * <code>close</code> method.
62 *
63 * @param e an enumeration of input streams.
64 * @see java.util.Enumeration
65 */
66 public SequenceInputStream(Enumeration<? extends InputStream> e) {
67 this.e = e;
68 peekNextStream();
69 }
70
71 /**
72 * Initializes a newly
73 * created <code>SequenceInputStream</code>
74 * by remembering the two arguments, which
75 * will be read in order, first <code>s1</code>
76 * and then <code>s2</code>, to provide the
77 * bytes to be read from this <code>SequenceInputStream</code>.
78 *
79 * @param s1 the first input stream to read.
80 * @param s2 the second input stream to read.
81 */
82 public SequenceInputStream(InputStream s1, InputStream s2) {
83 Vector<InputStream> v = new Vector<>(2);
84 v.addElement(s1);
85 v.addElement(s2);
86 e = v.elements();
87 peekNextStream();
88 }
89
90 /**
91 * Continues reading in the next stream if an EOF is reached.
92 */
93 final void nextStream() throws IOException {
94 if (in != null) {
95 in.close();
96 }
97 peekNextStream();
98 }
99
100 private void peekNextStream() {
101 if (e.hasMoreElements()) {
102 in = (InputStream) e.nextElement();
103 if (in == null)
104 throw new NullPointerException();
105 } else {
106 in = null;
107 }
108 }
109
110 /**
111 * Returns an estimate of the number of bytes that can be read (or
112 * skipped over) from the current underlying input stream without
113 * blocking by the next invocation of a method for the current
114 * underlying input stream. The next invocation might be
115 * the same thread or another thread. A single read or skip of this
116 * many bytes will not block, but may read or skip fewer bytes.
117 * <p>
118 * This method simply calls {@code available} of the current underlying
119 * input stream and returns the result.
120 *
121 * @return an estimate of the number of bytes that can be read (or
122 * skipped over) from the current underlying input stream
123 * without blocking or {@code 0} if this input stream
124 * has been closed by invoking its {@link #close()} method
125 * @exception IOException if an I/O error occurs.
126 *
127 * @since 1.1
128 */
129 public int available() throws IOException {
130 if (in == null) {
131 return 0; // no way to signal EOF from available()
132 }
133 return in.available();
134 }
135
136 /**
137 * Reads the next byte of data from this input stream. The byte is
138 * returned as an <code>int</code> in the range <code>0</code> to
139 * <code>255</code>. If no byte is available because the end of the
140 * stream has been reached, the value <code>-1</code> is returned.
141 * This method blocks until input data is available, the end of the
142 * stream is detected, or an exception is thrown.
143 * <p>
144 * This method
145 * tries to read one character from the current substream. If it
146 * reaches the end of the stream, it calls the <code>close</code>
147 * method of the current substream and begins reading from the next
148 * substream.
149 *
150 * @return the next byte of data, or <code>-1</code> if the end of the
151 * stream is reached.
152 * @exception IOException if an I/O error occurs.
153 */
154 public int read() throws IOException {
155 while (in != null) {
156 int c = in.read();
157 if (c != -1) {
158 return c;
159 }
160 nextStream();
161 }
162 return -1;
163 }
164
165 /**
166 * Reads up to <code>len</code> bytes of data from this input stream
167 * into an array of bytes. If <code>len</code> is not zero, the method
168 * blocks until at least 1 byte of input is available; otherwise, no
169 * bytes are read and <code>0</code> is returned.
170 * <p>
171 * The <code>read</code> method of <code>SequenceInputStream</code>
172 * tries to read the data from the current substream. If it fails to
173 * read any characters because the substream has reached the end of
174 * the stream, it calls the <code>close</code> method of the current
175 * substream and begins reading from the next substream.
176 *
177 * @param b the buffer into which the data is read.
178 * @param off the start offset in array <code>b</code>
179 * at which the data is written.
180 * @param len the maximum number of bytes read.
181 * @return int the number of bytes read.
182 * @exception NullPointerException If <code>b</code> is <code>null</code>.
183 * @exception IndexOutOfBoundsException If <code>off</code> is negative,
184 * <code>len</code> is negative, or <code>len</code> is greater than
185 * <code>b.length - off</code>
186 * @exception IOException if an I/O error occurs.
187 */
188 public int read(byte b[], int off, int len) throws IOException {
189 if (in == null) {
190 return -1;
191 } else if (b == null) {
192 throw new NullPointerException();
193 } else if (off < 0 || len < 0 || len > b.length - off) {
194 throw new IndexOutOfBoundsException();
195 } else if (len == 0) {
196 return 0;
197 }
198 do {
199 int n = in.read(b, off, len);
200 if (n > 0) {
201 return n;
202 }
203 nextStream();
204 } while (in != null);
205 return -1;
206 }
207
208 /**
209 * Closes this input stream and releases any system resources
210 * associated with the stream.
211 * A closed <code>SequenceInputStream</code>
212 * cannot perform input operations and cannot
213 * be reopened.
214 * <p>
215 * If this stream was created
216 * from an enumeration, all remaining elements
217 * are requested from the enumeration and closed
218 * before the <code>close</code> method returns.
219 *
220 * @exception IOException if an I/O error occurs.
221 */
222 public void close() throws IOException {
223 do {
224 nextStream();
225 } while (in != null);
226 }
227 }