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Lucene example source code file (ChecksumIndexOutput.java)

This example Lucene source code file (ChecksumIndexOutput.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

checksum, checksumindexoutput, checksumindexoutput, crc32, indexoutput, indexoutput, io, ioexception, ioexception, override, override, runtimeexception, zip

The Lucene ChecksumIndexOutput.java source code

package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

import java.io.IOException;
import java.util.zip.CRC32;
import java.util.zip.Checksum;

/** Writes bytes through to a primary IndexOutput, computing
 *  checksum.  Note that you cannot use seek().
 *
 * @lucene.internal
 */
public class ChecksumIndexOutput extends IndexOutput {
  IndexOutput main;
  Checksum digest;

  public ChecksumIndexOutput(IndexOutput main) {
    this.main = main;
    digest = new CRC32();
  }

  @Override
  public void writeByte(byte b) throws IOException {
    digest.update(b);
    main.writeByte(b);
  }

  @Override
  public void writeBytes(byte[] b, int offset, int length) throws IOException {
    digest.update(b, offset, length);
    main.writeBytes(b, offset, length);
  }

  public long getChecksum() {
    return digest.getValue();
  }

  @Override
  public void flush() throws IOException {
    main.flush();
  }

  @Override
  public void close() throws IOException {
    main.close();
  }

  @Override
  public long getFilePointer() {
    return main.getFilePointer();
  }

  @Override
  public void seek(long pos) {
    throw new RuntimeException("not allowed");    
  }

  /**
   * Starts but does not complete the commit of this file (=
   * writing of the final checksum at the end).  After this
   * is called must call {@link #finishCommit} and the
   * {@link #close} to complete the commit.
   */
  public void prepareCommit() throws IOException {
    final long checksum = getChecksum();
    // Intentionally write a mismatched checksum.  This is
    // because we want to 1) test, as best we can, that we
    // are able to write a long to the file, but 2) not
    // actually "commit" the file yet.  This (prepare
    // commit) is phase 1 of a two-phase commit.
    final long pos = main.getFilePointer();
    main.writeLong(checksum-1);
    main.flush();
    main.seek(pos);
  }

  /** See {@link #prepareCommit} */
  public void finishCommit() throws IOException {
    main.writeLong(getChecksum());
  }

  @Override
  public long length() throws IOException {
    return main.length();
  }
}

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