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


1 /* RepositionableInputStream.java
2  *
3  * $Id: RepositionableInputStream.java,v 1.3.6.1 2007/01/13 01:31:34 stack-sf Exp $
4  *
5  * Created Dec 20, 2005
6  *
7  * Copyright (C) 2005 Internet Archive.
8  *
9  * This file is part of the Heritrix web crawler (crawler.archive.org).
10  *
11  * Heritrix is free software; you can redistribute it and/or modify
12  * it under the terms of the GNU Lesser Public License as published by
13  * the Free Software Foundation; either version 2.1 of the License, or
14  * any later version.
15  *
16  * Heritrix is distributed in the hope that it will be useful,
17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19  * GNU Lesser Public License for more details.
20  *
21  * You should have received a copy of the GNU Lesser Public License
22  * along with Heritrix; if not, write to the Free Software
23  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
24  */
25 package org.archive.io;
26
27 import it.unimi.dsi.fastutil.io.RepositionableStream;
28
29 import java.io.BufferedInputStream JavaDoc;
30 import java.io.IOException JavaDoc;
31 import java.io.InputStream JavaDoc;
32
33 /**
34  * Wrapper around an {@link InputStream} to make a primitive Repositionable
35  * stream. Uses a {@link BufferedInputStream}. Calls mark on every read so
36  * we'll remember at least the last thing read (You can only backup on the
37  * last thing read -- not last 2 or 3 things read). Used by
38  * {@link GzippedInputStream} when reading streams over a network. Wraps a
39  * HTTP, etc., stream so we can back it up if needs be after the
40  * GZIP inflater has done a fill of its full buffer though it only needed
41  * the first few bytes to finish decompressing the current GZIP member.
42  *
43  * <p>TODO: More robust implementation. Tried to use the it.unimi.dsi.io
44  * FastBufferdInputStream but relies on FileChannel ByteBuffers and if not
45  * present -- as would be the case reading from a network stream, the main
46  * application for this instance -- then it expects the underlying stream
47  * implements RepositionableStream interface so chicken or egg problem.
48  * @author stack
49  */
50 public class RepositionableInputStream extends BufferedInputStream JavaDoc implements
51         RepositionableStream {
52     private long position = 0;
53     private long markPosition = -1;
54     
55     public RepositionableInputStream(InputStream JavaDoc in) {
56         super(in);
57     }
58     
59     public RepositionableInputStream(InputStream JavaDoc in, int size) {
60         super(in, size);
61     }
62
63     public int read(byte[] b) throws IOException JavaDoc {
64         int read = super.read(b);
65         if (read != -1) {
66             position += read;
67         }
68         return read;
69     }
70     
71     public synchronized int read(byte[] b, int offset, int ct)
72     throws IOException JavaDoc {
73         // Mark the underlying stream so that we'll remember what we are about
74 // to read unless a mark has been set in this RepositionableStream
75 // (We have two levels of mark). In this latter case we want the
76 // underlying stream to preserve its mark position so aligns with
77 // this RS when eset is called.
78 if (!isMarked()) {
79             super.mark((ct > offset)? ct - offset: ct);
80         }
81         int read = super.read(b, offset, ct);
82         if (read != -1) {
83             position += read;
84         }
85         return read;
86     }
87     
88     public int read() throws IOException JavaDoc {
89         // Mark the underlying stream so that we'll remember what we are about
90 // to read unless a mark has been set in this RepositionableStream
91 // (We have two levels of mark). In this latter case we want the
92 // underlying stream to preserve its mark position so aligns with
93 // this RS when eset is called.
94 if (!isMarked()) {
95             super.mark(1);
96         }
97         int c = super.read();
98         if (c != -1) {
99             position++;
100         }
101         return c;
102     }
103
104     public void position(final long offset) {
105         if (this.position == offset) {
106             return;
107         }
108         int diff = (int)(offset - this.position);
109         long lowerBound = this.position - this.pos;
110         long upperBound = lowerBound + this.count;
111         if (offset < lowerBound || offset >= upperBound) {
112             throw new IllegalAccessError JavaDoc("Offset goes outside " +
113                 "current this.buf (TODO: Do buffer fills if positive)");
114         }
115         this.position = offset;
116         this.pos += diff;
117         // Clear any mark.
118 this.markPosition = -1;
119     }
120
121     public void mark(int readlimit) {
122         this.markPosition = this.position;
123         super.mark(readlimit);
124     }
125
126     public void reset() throws IOException JavaDoc {
127         super.reset();
128         this.position = this.markPosition;
129         this.markPosition = -1;
130     }
131     
132     protected boolean isMarked() {
133         return this.markPosition != -1;
134     }
135
136     public long position() {
137         return this.position;
138     }
139 }
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