DigestOutputStream


1   /*
2    * @(#)DigestOutputStream.java  1.31 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.security;
9   
10  import java.io.IOException  ;
11  import java.io.EOFException  ;
12  import java.io.OutputStream  ;
13  import java.io.FilterOutputStream  ;
14  import java.io.PrintStream  ;
15  import java.io.ByteArrayOutputStream  ;
16  
17  /**
18   * A transparent stream that updates the associated message digest using
19   * the bits going through the stream.
20   *
21   * <p>To complete the message digest computation, call one of the
22   * <code>digest</code> methods on the associated message
23   * digest after your calls to one of this digest ouput stream's
24   * {@link #write(int) write} methods.
25   *
26   * <p>It is possible to turn this stream on or off (see
27   * {@link #on(boolean) on}). When it is on, a call to one of the
28   * <code>write</code> methods results in
29   * an update on the message digest.  But when it is off, the message
30   * digest is not updated. The default is for the stream to be on.
31   *
32   * @see MessageDigest
33   * @see DigestInputStream
34   *
35   * @version 1.31 03/12/19
36   * @author Benjamin Renaud
37   */
38  public class DigestOutputStream extends FilterOutputStream   {
39  
40      private boolean on = true;
41  
42      /**
43       * The message digest associated with this stream.
44       */
45      protected MessageDigest   digest;
46  
47      /**
48       * Creates a digest output stream, using the specified output stream
49       * and message digest.
50       *
51       * @param stream the output stream.
52       *
53       * @param digest the message digest to associate with this stream.
54       */
55      public DigestOutputStream(OutputStream   stream, MessageDigest   digest) {
56      super(stream);
57      setMessageDigest(digest);
58      }
59  
60      /**
61       * Returns the message digest associated with this stream.
62       *
63       * @return the message digest associated with this stream.
64       * @see #setMessageDigest(java.security.MessageDigest)
65       */
66      public MessageDigest   getMessageDigest() {
67      return digest;
68      }
69  
70      /**
71       * Associates the specified message digest with this stream.
72       *
73       * @param digest the message digest to be associated with this stream.
74       * @see #getMessageDigest()
75       */
76      public void setMessageDigest(MessageDigest   digest) {
77      this.digest = digest;
78      }
79  
80      /**
81       * Updates the message digest (if the digest function is on) using
82       * the specified byte, and in any case writes the byte
83       * to the output stream. That is, if the digest function is on
84       * (see {@link #on(boolean) on}), this method calls
85       * <code>update</code> on the message digest associated with this
86       * stream, passing it the byte <code>b</code>. This method then
87       * writes the byte to the output stream, blocking until the byte
88       * is actually written.
89       *
90       * @param b the byte to be used for updating and writing to the
91       * output stream.
92       *
93       * @exception IOException if an I/O error occurs.
94       *
95       * @see MessageDigest#update(byte)
96       */
97      public void write(int b) throws IOException   {
98      if (on) {
99          digest.update((byte)b);
100     }
101     out.write(b);
102     }
103 
104     /**
105      * Updates the message digest (if the digest function is on) using
106      * the specified subarray, and in any case writes the subarray to
107      * the output stream. That is, if the digest function is on (see
108      * {@link #on(boolean) on}), this method calls <code>update</code>
109      * on the message digest associated with this stream, passing it
110      * the subarray specifications. This method then writes the subarray
111      * bytes to the output stream, blocking until the bytes are actually
112      * written.
113      *
114      * @param b the array containing the subarray to be used for updating
115      * and writing to the output stream.
116      *
117      * @param off the offset into <code>b</code> of the first byte to
118      * be updated and written.
119      *
120      * @param len the number of bytes of data to be updated and written
121      * from <code>b</code>, starting at offset <code>off</code>.
122      *
123      * @exception IOException if an I/O error occurs.
124      *
125      * @see MessageDigest#update(byte[], int, int)
126      */
127     public void write(byte[] b, int off, int len) throws IOException   {
128     if (on) {
129         digest.update(b, off, len);
130     }
131     out.write(b, off, len);
132     }
133 
134     /**
135      * Turns the digest function on or off. The default is on.  When
136      * it is on, a call to one of the <code>write</code> methods results in an
137      * update on the message digest.  But when it is off, the message
138      * digest is not updated.
139      *
140      * @param on true to turn the digest function on, false to turn it
141      * off.
142      */
143     public void on(boolean on) {
144     this.on = on;
145     }
146 
147     /**
148      * Prints a string representation of this digest output stream and
149      * its associated message digest object.
150      */
151      public String   toString() {
152      return "[Digest Output Stream] " + digest.toString();
153      }
154 }
155 
156 
157 
158 
159
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