CheckedInputStream.java revision 51b1b6997fd3f980076b8081f7f1165ccc2a4008 
1/*
2 * Copyright (c) 1996, 2006, 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
26package java.util.zip;
27
28import java.io.FilterInputStream;
29import java.io.InputStream;
30import java.io.IOException;
31
32/**
33 * An input stream that also maintains a checksum of the data being read.
34 * The checksum can then be used to verify the integrity of the input data.
35 *
36 * @see         Checksum
37 * @author      David Connelly
38 */
39public
40class CheckedInputStream extends FilterInputStream {
41    private Checksum cksum;
42
43    /**
44     * Creates an input stream using the specified Checksum.
45     * @param in the input stream
46     * @param cksum the Checksum
47     */
48    public CheckedInputStream(InputStream in, Checksum cksum) {
49        super(in);
50        this.cksum = cksum;
51    }
52
53    /**
54     * Reads a byte. Will block if no input is available.
55     * @return the byte read, or -1 if the end of the stream is reached.
56     * @exception IOException if an I/O error has occurred
57     */
58    public int read() throws IOException {
59        int b = in.read();
60        if (b != -1) {
61            cksum.update(b);
62        }
63        return b;
64    }
65
66    /**
67     * Reads into an array of bytes. If <code>len</code> is not zero, the method
68     * blocks until some input is available; otherwise, no
69     * bytes are read and <code>0</code> is returned.
70     * @param buf the buffer into which the data is read
71     * @param off the start offset in the destination array <code>b</code>
72     * @param len the maximum number of bytes read
73     * @return    the actual number of bytes read, or -1 if the end
74     *            of the stream is reached.
75     * @exception  NullPointerException If <code>buf</code> is <code>null</code>.
76     * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
77     * <code>len</code> is negative, or <code>len</code> is greater than
78     * <code>buf.length - off</code>
79     * @exception IOException if an I/O error has occurred
80     */
81    public int read(byte[] buf, int off, int len) throws IOException {
82        len = in.read(buf, off, len);
83        if (len != -1) {
84            cksum.update(buf, off, len);
85        }
86        return len;
87    }
88
89    /**
90     * Skips specified number of bytes of input.
91     * @param n the number of bytes to skip
92     * @return the actual number of bytes skipped
93     * @exception IOException if an I/O error has occurred
94     */
95    public long skip(long n) throws IOException {
96        byte[] buf = new byte[512];
97        long total = 0;
98        while (total < n) {
99            long len = n - total;
100            len = read(buf, 0, len < buf.length ? (int)len : buf.length);
101            if (len == -1) {
102                return total;
103            }
104            total += len;
105        }
106        return total;
107    }
108
109    /**
110     * Returns the Checksum for this input stream.
111     * @return the Checksum value
112     */
113    public Checksum getChecksum() {
114        return cksum;
115    }
116}
117