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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      */
SequenceInputStream(Enumeration<? extends InputStream> e)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      */
SequenceInputStream(InputStream s1, InputStream s2)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      */
nextStream()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      */
available()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      */
read()162     public int read() throws IOException {
163         while (in != null) {
164             int c = in.read();
165             if (c != -1) {
166                 return c;
167             }
168             nextStream();
169         }
170         return -1;
171     }
172 
173     /**
174      * Reads up to <code>len</code> bytes of data from this input stream
175      * into an array of bytes.  If <code>len</code> is not zero, the method
176      * blocks until at least 1 byte of input is available; otherwise, no
177      * bytes are read and <code>0</code> is returned.
178      * <p>
179      * The <code>read</code> method of <code>SequenceInputStream</code>
180      * tries to read the data from the current substream. If it fails to
181      * read any characters because the substream has reached the end of
182      * the stream, it calls the <code>close</code> method of the current
183      * substream and begins reading from the next substream.
184      *
185      * @param      b     the buffer into which the data is read.
186      * @param      off   the start offset in array <code>b</code>
187      *                   at which the data is written.
188      * @param      len   the maximum number of bytes read.
189      * @return     int   the number of bytes read.
190      * @exception  NullPointerException If <code>b</code> is <code>null</code>.
191      * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
192      * <code>len</code> is negative, or <code>len</code> is greater than
193      * <code>b.length - off</code>
194      * @exception  IOException  if an I/O error occurs.
195      */
read(byte b[], int off, int len)196     public int read(byte b[], int off, int len) throws IOException {
197         if (in == null) {
198             return -1;
199         } else if (b == null) {
200             throw new NullPointerException();
201         } else if (off < 0 || len < 0 || len > b.length - off) {
202             throw new IndexOutOfBoundsException();
203         } else if (len == 0) {
204             return 0;
205         }
206         do {
207             int n = in.read(b, off, len);
208             if (n > 0) {
209                 return n;
210             }
211             nextStream();
212         } while (in != null);
213         return -1;
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      */
close()230     public void close() throws IOException {
231         do {
232             nextStream();
233         } while (in != null);
234     }
235 }
236