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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   JDK1.0
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          try {
69              nextStream();
70          } catch (IOException ex) {
71              // This should never happen
72              throw new Error("panic");
73          }
74      }
75  
76      /**
77       * Initializes a newly
78       * created <code>SequenceInputStream</code>
79       * by remembering the two arguments, which
80       * will be read in order, first <code>s1</code>
81       * and then <code>s2</code>, to provide the
82       * bytes to be read from this <code>SequenceInputStream</code>.
83       *
84       * @param   s1   the first input stream to read.
85       * @param   s2   the second input stream to read.
86       */
87      public SequenceInputStream(InputStream s1, InputStream s2) {
88          Vector<InputStream> v = new Vector<>(2);
89  
90          v.addElement(s1);
91          v.addElement(s2);
92          e = v.elements();
93          try {
94              nextStream();
95          } catch (IOException ex) {
96              // This should never happen
97              throw new Error("panic");
98          }
99      }
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         }
114         else 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 }