    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 messageDigest;
    039
    040        /**
    041         * Creates an MessageDigestMaintainingObserver for the given MessageDigest.
    042         * @param messageDigest the message digest to use
    043         */
    044        public MessageDigestMaintainingObserver(final MessageDigest messageDigest) {
    045            this.messageDigest = messageDigest;
    046        }
    047
    048        @Override
    049        public void data(final int input) throws IOException {
    050            messageDigest.update((byte) input);
    051        }
    052
    053        @Override
    054        public void data(final byte[] input, final int offset, final int length) throws IOException {
    055            messageDigest.update(input, offset, length);
    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 inputStream the stream to calculate the message digest for
    064     * @param MessageDigest the message digest to use
    065     */
    066    public MessageDigestCalculatingInputStream(final InputStream inputStream, final MessageDigest MessageDigest) {
    067        super(inputStream);
    068        this.messageDigest = MessageDigest;
    069        add(new MessageDigestMaintainingObserver(MessageDigest));
    070    }
    071
    072    /**
    073     * Creates a new instance, which calculates a signature on the given stream, using a {@link MessageDigest} with the
    074     * given algorithm.
    075     *
    076     * @param inputStream the stream to calculate the message digest for
    077     * @param algorithm the name of the algorithm to use
    078     * @throws NoSuchAlgorithmException if no Provider supports a MessageDigestSpi implementation for the specified
    079     *         algorithm.
    080     */
    081    public MessageDigestCalculatingInputStream(final InputStream inputStream, final String algorithm)
    082        throws NoSuchAlgorithmException {
    083        this(inputStream, MessageDigest.getInstance(algorithm));
    084    }
    085
    086    /**
    087     * Creates a new instance, which calculates a signature on the given stream, using a {@link MessageDigest} with the
    088     * "MD5" algorithm.
    089     *
    090     * @param inputStream the stream to calculate the message digest for
    091     * @throws NoSuchAlgorithmException if no Provider supports a MessageDigestSpi implementation for the specified
    092     *         algorithm.
    093     */
    094    public MessageDigestCalculatingInputStream(final InputStream inputStream) throws NoSuchAlgorithmException {
    095        this(inputStream, MessageDigest.getInstance("MD5"));
    096    }
    097
    098    /** Returns the {@link MessageDigest}, which is being used for generating the
    099     * checksum.
    100     * <em>Note</em>: The checksum will only reflect the data, which has been read so far.
    101     * This is probably not, what you expect. Make sure, that the complete data has been
    102     * read, if that is what you want. The easiest way to do so is by invoking
    103     * {@link #consume()}.
    104     * @return the message digest used
    105     */
    106    public MessageDigest getMessageDigest() {
    107        return messageDigest;
    108    }
    109}