org.apache.hadoop.io.DataOutputBuffer.java Source code

Introduction

Here is the source code for org.apache.hadoop.io.DataOutputBuffer.java

Source

/**
 * 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.
 */

package org.apache.hadoop.io;

import java.io.*;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

import com.google.common.base.Preconditions;

/** A reusable {@link DataOutput} implementation that writes to an in-memory
 * buffer.
 *
 * <p>This saves memory over creating a new DataOutputStream and
 * ByteArrayOutputStream each time data is written.
 *
 * <p>Typical usage is something like the following:<pre>
 *
 * DataOutputBuffer buffer = new DataOutputBuffer();
 * while (... loop condition ...) {
 *   buffer.reset();
 *   ... write buffer using DataOutput methods ...
 *   byte[] data = buffer.getData();
 *   int dataLength = buffer.getLength();
 *   ... write data to its ultimate destination ...
 * }
 * </pre>
 *  
 */
@InterfaceAudience.LimitedPrivate({ "HDFS", "MapReduce" })
@InterfaceStability.Unstable
public class DataOutputBuffer extends DataOutputStream {

    private static class Buffer extends ByteArrayOutputStream {
        public byte[] getData() {
            return buf;
        }

        public int getLength() {
            return count;
        }

        public Buffer() {
            super();
        }

        public Buffer(int size) {
            super(size);
        }

        public void write(DataInput in, int len) throws IOException {
            int newcount = count + len;
            if (newcount > buf.length) {
                byte newbuf[] = new byte[Math.max(buf.length << 1, newcount)];
                System.arraycopy(buf, 0, newbuf, 0, count);
                buf = newbuf;
            }
            in.readFully(buf, count, len);
            count = newcount;
        }

        /**
         * Set the count for the current buf.
         * @param newCount the new count to set
         * @return the original count
         */
        private int setCount(int newCount) {
            Preconditions.checkArgument(newCount >= 0 && newCount <= buf.length);
            int oldCount = count;
            count = newCount;
            return oldCount;
        }
    }

    private Buffer buffer;

    /** Constructs a new empty buffer. */
    public DataOutputBuffer() {
        this(new Buffer());
    }

    public DataOutputBuffer(int size) {
        this(new Buffer(size));
    }

    private DataOutputBuffer(Buffer buffer) {
        super(buffer);
        this.buffer = buffer;
    }

    /** Returns the current contents of the buffer.
     *  Data is only valid to {@link #getLength()}.
     */
    public byte[] getData() {
        return buffer.getData();
    }

    /** Returns the length of the valid data currently in the buffer. */
    public int getLength() {
        return buffer.getLength();
    }

    /** Resets the buffer to empty. */
    public DataOutputBuffer reset() {
        this.written = 0;
        buffer.reset();
        return this;
    }

    /** Writes bytes from a DataInput directly into the buffer. */
    public void write(DataInput in, int length) throws IOException {
        buffer.write(in, length);
    }

    /** Write to a file stream */
    public void writeTo(OutputStream out) throws IOException {
        buffer.writeTo(out);
    }

    /**
     * Overwrite an integer into the internal buffer. Note that this call can only
     * be used to overwrite existing data in the buffer, i.e., buffer#count cannot
     * be increased, and DataOutputStream#written cannot be increased.
     */
    public void writeInt(int v, int offset) throws IOException {
        Preconditions.checkState(offset + 4 <= buffer.getLength());
        byte[] b = new byte[4];
        b[0] = (byte) ((v >>> 24) & 0xFF);
        b[1] = (byte) ((v >>> 16) & 0xFF);
        b[2] = (byte) ((v >>> 8) & 0xFF);
        b[3] = (byte) ((v >>> 0) & 0xFF);
        int oldCount = buffer.setCount(offset);
        buffer.write(b);
        buffer.setCount(oldCount);
    }
}