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      1 /*
      2  *  Licensed to the Apache Software Foundation (ASF) under one or more
      3  *  contributor license agreements.  See the NOTICE file distributed with
      4  *  this work for additional information regarding copyright ownership.
      5  *  The ASF licenses this file to You under the Apache License, Version 2.0
      6  *  (the "License"); you may not use this file except in compliance with
      7  *  the License.  You may obtain a copy of the License at
      8  *
      9  *     http://www.apache.org/licenses/LICENSE-2.0
     10  *
     11  *  Unless required by applicable law or agreed to in writing, software
     12  *  distributed under the License is distributed on an "AS IS" BASIS,
     13  *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     14  *  See the License for the specific language governing permissions and
     15  *  limitations under the License.
     16  */
     17 
     18 package java.security;
     19 
     20 import java.io.FilterOutputStream;
     21 import java.io.IOException;
     22 import java.io.OutputStream;
     23 
     24 /**
     25  * {@code DigestOutputStream} is a {@code FilterOutputStream} which maintains an
     26  * associated message digest.
     27  */
     28 public class DigestOutputStream extends FilterOutputStream {
     29 
     30     /**
     31      * The message digest for this stream.
     32      */
     33     protected MessageDigest digest;
     34 
     35     // Indicates whether digest functionality is on or off
     36     private boolean isOn = true;
     37 
     38     /**
     39      * Constructs a new instance of this {@code DigestOutputStream}, using the
     40      * given {@code stream} and the {@code digest}.
     41      *
     42      * @param stream
     43      *            the output stream.
     44      * @param digest
     45      *            the message digest.
     46      */
     47     public DigestOutputStream(OutputStream stream, MessageDigest digest) {
     48         super(stream);
     49         this.digest = digest;
     50     }
     51 
     52     /**
     53      * Returns the message digest for this stream.
     54      *
     55      * @return the message digest for this stream.
     56      */
     57     public MessageDigest getMessageDigest() {
     58         return digest;
     59     }
     60 
     61     /**
     62      * Sets the message digest which this stream will use.
     63      *
     64      * @param digest
     65      *            the message digest which this stream will use.
     66      */
     67     public void setMessageDigest(MessageDigest digest) {
     68         this.digest = digest;
     69     }
     70 
     71     /**
     72      * Writes the specified {@code int} to the stream. Updates the digest if
     73      * this function is {@link #on(boolean)}.
     74      *
     75      * @param b
     76      *            the byte to be written.
     77      * @throws IOException
     78      *             if writing to the stream causes a {@code IOException}
     79      */
     80     @Override
     81     public void write(int b) throws IOException {
     82         // update digest only if digest functionality is on
     83         if (isOn) {
     84             digest.update((byte)b);
     85         }
     86         // write the byte
     87         out.write(b);
     88     }
     89 
     90     /**
     91      * Writes {@code len} bytes into the stream, starting from the specified
     92      * offset. Updates the digest if this function is {@link #on(boolean)}.
     93      *
     94      * @param b
     95      *            the buffer to write to.
     96      * @param off
     97      *            the index of the first byte in {@code b} to write.
     98      * @param len
     99      *            the number of bytes in {@code b} to write.
    100      * @throws IOException
    101      *             if writing to the stream causes an {@code IOException}.
    102      */
    103     @Override
    104     public void write(byte[] b, int off, int len) throws IOException {
    105         // update digest only if digest functionality is on
    106         if (isOn) {
    107             digest.update(b, off, len);
    108         }
    109         // write len bytes
    110         out.write(b, off, len);
    111     }
    112 
    113     /**
    114      * Enables or disables the digest function (default is on).
    115      *
    116      * @param on
    117      *            {@code true} if the digest should be computed, {@code false}
    118      *            otherwise.
    119      * @see MessageDigest
    120      */
    121     public void on(boolean on) {
    122         isOn = on;
    123     }
    124 
    125     /**
    126      * Returns a string containing a concise, human-readable description of this
    127      * {@code DigestOutputStream} including the digest.
    128      *
    129      * @return a printable representation for this {@code DigestOutputStream}.
    130      */
    131     @Override
    132     public String toString() {
    133         return super.toString() + ", " + digest.toString() +
    134             (isOn ? ", is on" : ", is off");
    135     }
    136 }
    137