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

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Here is the source code for org.apache.hadoop.io.ArrayFile.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 java.io.*;
import org.apache.hadoop.fs.*;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.util.*;
import org.apache.hadoop.io.SequenceFile.CompressionType;

/** A dense file-based mapping from integers to values. */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class ArrayFile extends MapFile {

    protected ArrayFile() {
    } // no public ctor

    /** Write a new array file. */
    public static class Writer extends MapFile.Writer {
        private LongWritable count = new LongWritable(0);

        /** Create the named file for values of the named class. */
        public Writer(Configuration conf, FileSystem fs, String file, Class<? extends Writable> valClass)
                throws IOException {
            super(conf, new Path(file), keyClass(LongWritable.class), valueClass(valClass));
        }

        /** Create the named file for values of the named class. */
        public Writer(Configuration conf, FileSystem fs, String file, Class<? extends Writable> valClass,
                CompressionType compress, Progressable progress) throws IOException {
            super(conf, new Path(file), keyClass(LongWritable.class), valueClass(valClass), compression(compress),
                    progressable(progress));
        }

        /** Append a value to the file. */
        public synchronized void append(Writable value) throws IOException {
            super.append(count, value); // add to map
            count.set(count.get() + 1); // increment count
        }
    }

    /** Provide access to an existing array file. */
    public static class Reader extends MapFile.Reader {
        private LongWritable key = new LongWritable();

        /** Construct an array reader for the named file.*/
        public Reader(FileSystem fs, String file, Configuration conf) throws IOException {
            super(new Path(file), conf);
        }

        /** Positions the reader before its <code>n</code>th value. */
        public synchronized void seek(long n) throws IOException {
            key.set(n);
            seek(key);
        }

        /** Read and return the next value in the file. */
        public synchronized Writable next(Writable value) throws IOException {
            return next(key, value) ? value : null;
        }

        /** Returns the key associated with the most recent call to {@link
         * #seek(long)}, {@link #next(Writable)}, or {@link
         * #get(long,Writable)}. */
        public synchronized long key() throws IOException {
            return key.get();
        }

        /** Return the <code>n</code>th value in the file. */
        public synchronized Writable get(long n, Writable value) throws IOException {
            key.set(n);
            return get(key, value);
        }
    }

}