fsinputstream.java

hadoop:Nutch集群平台

/**
 * Copyright 2005 The Apache Software Foundation
 *
 * 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 org.apache.hadoop.fs;

import java.io.*;

/****************************************************************
 * FSInputStream is a generic old InputStream with a little bit
 * of RAF-style seek ability.
 *
 * @author Mike Cafarella
 *****************************************************************/
public abstract class FSInputStream extends InputStream
    implements Seekable, PositionedReadable {
    /**
     * Seek to the given offset from the start of the file.
     * The next read() will be from that location.  Can't
     * seek past the end of the file.
     */
    public abstract void seek(long pos) throws IOException;

    /**
     * Return the current offset from the start of the file
     */
    public abstract long getPos() throws IOException;
    
    public int read(long position, byte[] buffer, int offset, int length)
    throws IOException {
      synchronized (this) {
        long oldPos = getPos();
        int nread = -1;
        try {
          seek(position);
          nread = read(buffer, offset, length);
        } finally {
          seek(oldPos);
        }
        return nread;
      }
    }
    
    public void readFully(long position, byte[] buffer, int offset, int length)
    throws IOException {
      int nread = 0;
      while (nread < length) {
        int nbytes = read(position+nread, buffer, offset+nread, length-nread);
        if (nbytes < 0) {
          throw new EOFException("End of file reached before reading fully.");
        }
        nread += nbytes;
      }
    }
    
    public void readFully(long position, byte[] buffer)
    throws IOException {
      readFully(position, buffer, 0, buffer.length);
    }
}