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


1 /* OriginSeekInputStream
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  * Alters the origin of some other SeekInputStream. This class allows you
31  * to completely ignore everything in the underlying stream before a specified
32  * position, the origin position.
33  *
34  * <p>With the exception of {@link #position()} and {@link position(long)},
35  * all of the methods in this class simply delegate to the underlying input
36  * stream. The <code>position</code> methods adjust the position of the
37  * underlying stream relative to the origin specified at construction time.
38  *
39  * @author pjack
40  */
41 public class OriginSeekInputStream extends SeekInputStream {
42
43
44     /**
45      * The underlying stream.
46      */
47     final private SeekInputStream input;
48
49
50     /**
51      * The origin position. In other words, this.position(0)
52      * resolves to input.position(start).
53      */
54     final private long origin;
55
56
57     /**
58      * Constructor.
59      *
60      * @param input the underlying stream
61      * @param origin the origin position
62      * @throws IOException if an IO error occurs
63      */
64     public OriginSeekInputStream(SeekInputStream input, long origin)
65     throws IOException JavaDoc {
66         this.input = input;
67         this.origin = origin;
68         input.position(origin);
69     }
70
71
72     @Override JavaDoc
73     public int available() throws IOException JavaDoc {
74         return input.available();
75     }
76
77
78     @Override JavaDoc
79     public int read() throws IOException JavaDoc {
80         return input.read();
81     }
82
83
84     @Override JavaDoc
85     public int read(byte[] buf, int ofs, int len) throws IOException JavaDoc {
86         return input.read(buf, ofs, len);
87     }
88
89
90     @Override JavaDoc
91     public int read(byte[] buf) throws IOException JavaDoc {
92         return input.read(buf);
93     }
94
95
96     @Override JavaDoc
97     public long skip(long count) throws IOException JavaDoc {
98         return input.skip(count);
99     }
100
101
102     /**
103      * Returns the position of the underlying stream relative to the origin.
104      *
105      * @return the relative position
106      * @throws IOException if an IO error occurs
107      */
108     public long position() throws IOException JavaDoc {
109         return input.position() - origin;
110     }
111
112
113     /**
114      * Positions the underlying stream relative to the origin.
115      * In other words, this.position(0) resolves to input.position(origin),
116      * where input is underlying stream and origin is the origin specified
117      * at construction time.
118      *
119      * @param p the new position for this stream
120      * @throws IOException if an IO error occurs
121      */
122     public void position(long p) throws IOException JavaDoc {
123         input.position(p + origin);
124     }
125 }
126
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