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

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

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

import java.io.ByteArrayInputStream;
import java.io.DataInputStream;

/** A reusable {@link java.io.DataInput} implementation
 * that reads from an in-memory buffer.
 *
 * <p>This saves memory over creating a new DataInputStream and
 * ByteArrayInputStream each time data is read.
 *
 * <p>Typical usage is something like the following:<pre>
 *
 * DataInputBuffer buffer = new DataInputBuffer();
 * while (... loop condition ...) {
 *   byte[] data = ... get data ...;
 *   int dataLength = ... get data length ...;
 *   buffer.reset(data, dataLength);
 *   ... read buffer using DataInput methods ...
 * }
 * </pre>
 *  
 */
@InterfaceAudience.LimitedPrivate({ "HDFS", "MapReduce" })
@InterfaceStability.Unstable
public class DataInputBuffer extends DataInputStream {
    private static class Buffer extends ByteArrayInputStream {
        public Buffer() {
            super(new byte[] {});
        }

        public void reset(byte[] input, int start, int length) {
            this.buf = input;
            this.count = start + length;
            this.mark = start;
            this.pos = start;
        }

        public byte[] getData() {
            return buf;
        }

        public int getPosition() {
            return pos;
        }

        public int getLength() {
            return count;
        }

        /* functions below comes verbatim from
         hive.common.io.NonSyncByteArrayInputStream */

        /**
         * {@inheritDoc}
         */
        @Override
        public int read() {
            return (pos < count) ? (buf[pos++] & 0xff) : -1;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int read(byte[] b, int off, int len) {
            if (b == null) {
                throw new NullPointerException();
            } else if (off < 0 || len < 0 || len > b.length - off) {
                throw new IndexOutOfBoundsException();
            }
            if (pos >= count) {
                return -1;
            }
            if (pos + len > count) {
                len = count - pos;
            }
            if (len <= 0) {
                return 0;
            }
            System.arraycopy(buf, pos, b, off, len);
            pos += len;
            return len;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public long skip(long n) {
            if (pos + n > count) {
                n = count - pos;
            }
            if (n < 0) {
                return 0;
            }
            pos += n;
            return n;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public int available() {
            return count - pos;
        }
    }

    private Buffer buffer;

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

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

    /** Resets the data that the buffer reads. */
    public void reset(byte[] input, int length) {
        buffer.reset(input, 0, length);
    }

    /** Resets the data that the buffer reads. */
    public void reset(byte[] input, int start, int length) {
        buffer.reset(input, start, length);
    }

    public byte[] getData() {
        return buffer.getData();
    }

    /** Returns the current position in the input. */
    public int getPosition() {
        return buffer.getPosition();
    }

    /**
     * Returns the index one greater than the last valid character in the input
     * stream buffer.
     */
    public int getLength() {
        return buffer.getLength();
    }

}