001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.io.input;
018
019import java.io.IOException;
020import java.io.InputStream;
021import java.security.MessageDigest;
022import java.security.NoSuchAlgorithmException;
023
024
025/**
026 * This class is an example for using an {@link ObservableInputStream}. It
027 * creates its own {@link org.apache.commons.io.input.ObservableInputStream.Observer},
028 * which calculates a checksum using a MessageDigest, for example an MD5 sum.
029 * <em>Note</em>: Neither {@link ObservableInputStream}, nor {@link MessageDigest},
030 * are thread safe. So is {@link MessageDigestCalculatingInputStream}.
031 */
032public class MessageDigestCalculatingInputStream extends ObservableInputStream {
033
034    /**
035     * Maintains the message digest.
036     */
037    public static class MessageDigestMaintainingObserver extends Observer {
038        private final MessageDigest md;
039
040        /**
041         * Creates an MessageDigestMaintainingObserver for the given MessageDigest.
042         * @param pMd the message digest to use
043         */
044        public MessageDigestMaintainingObserver(final MessageDigest pMd) {
045            md = pMd;
046        }
047
048        @Override
049        void data(final int pByte) throws IOException {
050            md.update((byte) pByte);
051        }
052
053        @Override
054        void data(final byte[] pBuffer, final int pOffset, final int pLength) throws IOException {
055            md.update(pBuffer, pOffset, pLength);
056        }
057    }
058
059    private final MessageDigest messageDigest;
060
061    /** Creates a new instance, which calculates a signature on the given stream,
062     * using the given {@link MessageDigest}.
063     * @param pStream the stream to calculate the message digest for
064     * @param pDigest the message digest to use
065     */
066    public MessageDigestCalculatingInputStream(final InputStream pStream, final MessageDigest pDigest) {
067        super(pStream);
068        messageDigest = pDigest;
069        add(new MessageDigestMaintainingObserver(pDigest));
070    }
071
072    /** Creates a new instance, which calculates a signature on the given stream,
073     * using a {@link MessageDigest} with the given algorithm.
074     * @param pStream the stream to calculate the message digest for
075     * @param pAlgorithm the name of the algorithm to use
076     * @throws NoSuchAlgorithmException if no Provider supports a MessageDigestSpi implementation for the specified algorithm.
077     */
078    public MessageDigestCalculatingInputStream(final InputStream pStream, final String pAlgorithm) throws NoSuchAlgorithmException {
079        this(pStream, MessageDigest.getInstance(pAlgorithm));
080    }
081
082    /** Creates a new instance, which calculates a signature on the given stream,
083     * using a {@link MessageDigest} with the "MD5" algorithm.
084     * @param pStream the stream to calculate the message digest for
085     * @throws NoSuchAlgorithmException if no Provider supports a MessageDigestSpi implementation for the specified algorithm.
086     */
087    public MessageDigestCalculatingInputStream(final InputStream pStream) throws NoSuchAlgorithmException {
088        this(pStream, MessageDigest.getInstance("MD5"));
089    }
090
091    /** Returns the {@link MessageDigest}, which is being used for generating the
092     * checksum.
093     * <em>Note</em>: The checksum will only reflect the data, which has been read so far.
094     * This is probably not, what you expect. Make sure, that the complete data has been
095     * read, if that is what you want. The easiest way to do so is by invoking
096     * {@link #consume()}.
097     * @return the message digest used
098     */
099    public MessageDigest getMessageDigest() {
100        return messageDigest;
101    }
102}