com.google.enterprise.connector.db.diffing.DigestContentHolder.java Source code

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Here is the source code for com.google.enterprise.connector.db.diffing.DigestContentHolder.java

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// Copyright 2013 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.enterprise.connector.db.diffing;

import com.google.common.base.Preconditions;
import com.google.enterprise.connector.db.InputStreamFactories;
import com.google.enterprise.connector.db.Util;
import com.google.enterprise.connector.util.Base16;
import com.google.enterprise.connector.util.InputStreamFactory;
import com.google.enterprise.connector.util.MimeTypeDetector;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * A {@link ContentHolder} that maintains an active MessageDigest to lazily
 * calculate the checksum. For some DocumentBuilder implementations, all
 * the components to calculating the checksum may not be readily available.
 * This keeps the MessageDigest active for updating until {@link #getChecksum()}
 * is called.
 */
public class DigestContentHolder extends ContentHolder {
    public static DigestContentHolder getInstance(byte[] contentBytes, MimeTypeDetector mimeTypeDetector) {
        Preconditions.checkNotNull(contentBytes);
        DigestContentHolder contentHolder = new DigestContentHolder(InputStreamFactories.newInstance(contentBytes),
                mimeTypeDetector.getMimeType(null, contentBytes), contentBytes.length);
        contentHolder.updateDigest(contentBytes);
        return contentHolder;
    }

    public static DigestContentHolder getEmptyInstance(String mimeType) {
        return new DigestContentHolder(InputStreamFactories.newInstance(new byte[0]), mimeType, 0);
    }

    private final int length;
    private final MessageDigest digest;
    private String checksum;

    private DigestContentHolder(InputStreamFactory content, String mimeType, int length) {
        super(content, null, mimeType);
        this.length = length;
        this.checksum = null;
        try {
            this.digest = MessageDigest.getInstance(Util.CHECKSUM_ALGO);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException("Could not get a message digest for " + Util.CHECKSUM_ALGO, e);
        }
    }

    public long getLength() {
        return length;
    }

    @Override
    public synchronized String getChecksum() {
        if (checksum == null) {
            checksum = Base16.lowerCase().encode(digest.digest());
        }
        return checksum;
    }

    /**
     * Updates the digest using the specified array of bytes.
     *
     * @param buf the array of bytes.
     */
    public synchronized void updateDigest(byte[] buf) {
        digest.update(buf);
    }
}