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Java > Open Source Codes > org > archive > io > SafeSeekInputStream


1 /* SafeSeekInputStream
2 *
3 * Created on September 14, 2006
4 *
5 * Copyright (C) 2006 Internet Archive.
6 *
7 * This file is part of the Heritrix web crawler (crawler.archive.org).
8 *
9 * Heritrix is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU Lesser Public License as published by
11 * the Free Software Foundation; either version 2.1 of the License, or
12 * any later version.
13 *
14 * Heritrix is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 * GNU Lesser Public License for more details.
18 *
19 * You should have received a copy of the GNU Lesser Public License
20 * along with Heritrix; if not, write to the Free Software
21 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
22 */
23 package org.archive.io;
24
25
26 import java.io.IOException JavaDoc;
27
28
29 /**
30  * Enables multiple concurrent streams based on the same underlying stream.
31  *
32  * @author pjack
33  */
34 public class SafeSeekInputStream extends SeekInputStream {
35
36
37     /**
38      * The underlying stream.
39      */
40     private SeekInputStream input;
41
42
43     /**
44      * The expected position of the underlying stream.
45      */
46     private long expected;
47
48
49     /**
50      * Constructor. The given stream will be positioned to 0 so that an
51      * accurate position can be tracked.
52      *
53      * @param input the underlying input stream
54      * @throws IOException if an IO error occurs
55      */
56     public SafeSeekInputStream(SeekInputStream input) throws IOException JavaDoc {
57         this.input = input;
58         this.expected = input.position();
59     }
60
61
62     /**
63      * Ensures that the underlying stream's position is what we expect to be.
64      *
65      * @throws IOException if an IO error occurs
66      */
67     private void ensure() throws IOException JavaDoc {
68         if (expected != input.position()) {
69             input.position(expected);
70         }
71     }
72
73
74     @Override JavaDoc
75     public int read() throws IOException JavaDoc {
76         ensure();
77         int c = input.read();
78         if (c >= 0) {
79             expected++;
80         }
81         return c;
82     }
83
84
85     @Override JavaDoc
86     public int read(byte[] buf, int ofs, int len) throws IOException JavaDoc {
87         ensure();
88         int r = input.read(buf, ofs, len);
89         if (r > 0) {
90             expected += r;
91         }
92         return r;
93     }
94
95
96     @Override JavaDoc
97     public int read(byte[] buf) throws IOException JavaDoc {
98         ensure();
99         int r = input.read(buf);
100         if (r > 0) {
101             expected += r;
102         }
103         return r;
104     }
105
106
107     @Override JavaDoc
108     public long skip(long c) throws IOException JavaDoc {
109         ensure();
110         long r = input.skip(c);
111         if (r > 0) {
112             expected += r;
113         }
114         return r;
115     }
116     
117     
118     public void position(long p) throws IOException JavaDoc {
119         input.position(p);
120         expected = p;
121     }
122
123
124     public long position() throws IOException JavaDoc {
125         return expected;
126     }
127
128 }
129
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