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
26package java.io;
27
28import java.io.InputStream;
29import java.util.Enumeration;
30import 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 */
45public
46class 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}
228