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Lucene example source code file (SimpleFSDirectory.java)

This example Lucene source code file (SimpleFSDirectory.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

bug, descriptor, descriptor, eof, file, io, ioexception, ioexception, object, outofmemoryerror, outofmemoryerror, override, override, simplefsdirectory, simplefsindexinput

The Lucene SimpleFSDirectory.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.File;
import java.io.IOException;
import java.io.RandomAccessFile;

/** A straightforward implementation of {@link FSDirectory}
 *  using java.io.RandomAccessFile.  However, this class has
 *  poor concurrent performance (multiple threads will
 *  bottleneck) as it synchronizes when multiple threads
 *  read from the same file.  It's usually better to use
 *  {@link NIOFSDirectory} or {@link MMapDirectory} instead. */
public class SimpleFSDirectory extends FSDirectory {
    
  /** Create a new SimpleFSDirectory for the named location.
   *
   * @param path the path of the directory
   * @param lockFactory the lock factory to use, or null for the default
   * ({@link NativeFSLockFactory});
   * @throws IOException
   */
  public SimpleFSDirectory(File path, LockFactory lockFactory) throws IOException {
    super(path, lockFactory);
  }
  
  /** Create a new SimpleFSDirectory for the named location and {@link NativeFSLockFactory}.
   *
   * @param path the path of the directory
   * @throws IOException
   */
  public SimpleFSDirectory(File path) throws IOException {
    super(path, null);
  }

  /** Creates an IndexInput for the file with the given name. */
  @Override
  public IndexInput openInput(String name, int bufferSize) throws IOException {
    ensureOpen();
    return new SimpleFSIndexInput(new File(directory, name), bufferSize, getReadChunkSize());
  }

  protected static class SimpleFSIndexInput extends BufferedIndexInput {
  
    protected static class Descriptor extends RandomAccessFile {
      // remember if the file is open, so that we don't try to close it
      // more than once
      protected volatile boolean isOpen;
      long position;
      final long length;
      
      public Descriptor(File file, String mode) throws IOException {
        super(file, mode);
        isOpen=true;
        length=length();
      }
  
      @Override
      public void close() throws IOException {
        if (isOpen) {
          isOpen=false;
          super.close();
        }
      }
    }
  
    protected final Descriptor file;
    boolean isClone;
    //  LUCENE-1566 - maximum read length on a 32bit JVM to prevent incorrect OOM 
    protected final int chunkSize;
    
    public SimpleFSIndexInput(File path, int bufferSize, int chunkSize) throws IOException {
      super(bufferSize);
      file = new Descriptor(path, "r");
      this.chunkSize = chunkSize;
    }
  
    /** IndexInput methods */
    @Override
    protected void readInternal(byte[] b, int offset, int len)
         throws IOException {
      synchronized (file) {
        long position = getFilePointer();
        if (position != file.position) {
          file.seek(position);
          file.position = position;
        }
        int total = 0;

        try {
          do {
            final int readLength;
            if (total + chunkSize > len) {
              readLength = len - total;
            } else {
              // LUCENE-1566 - work around JVM Bug by breaking very large reads into chunks
              readLength = chunkSize;
            }
            final int i = file.read(b, offset + total, readLength);
            if (i == -1) {
              throw new IOException("read past EOF");
            }
            file.position += i;
            total += i;
          } while (total < len);
        } catch (OutOfMemoryError e) {
          // propagate OOM up and add a hint for 32bit VM Users hitting the bug
          // with a large chunk size in the fast path.
          final OutOfMemoryError outOfMemoryError = new OutOfMemoryError(
              "OutOfMemoryError likely caused by the Sun VM Bug described in "
              + "https://issues.apache.org/jira/browse/LUCENE-1566; try calling FSDirectory.setReadChunkSize "
              + "with a value smaller than the current chunk size (" + chunkSize + ")");
          outOfMemoryError.initCause(e);
          throw outOfMemoryError;
        }
      }
    }
  
    @Override
    public void close() throws IOException {
      // only close the file if this is not a clone
      if (!isClone) file.close();
    }
  
    @Override
    protected void seekInternal(long position) {
    }
  
    @Override
    public long length() {
      return file.length;
    }
  
    @Override
    public Object clone() {
      SimpleFSIndexInput clone = (SimpleFSIndexInput)super.clone();
      clone.isClone = true;
      return clone;
    }
  
    /** Method used for testing. Returns true if the underlying
     *  file descriptor is valid.
     */
    boolean isFDValid() throws IOException {
      return file.getFD().valid();
    }
    
    @Override
    public void copyBytes(IndexOutput out, long numBytes) throws IOException {
      numBytes -= flushBuffer(out, numBytes);
      // If out is FSIndexOutput, the copy will be optimized
      out.copyBytes(this, numBytes);
    }
  }
}

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