org.apache.hadoop.io.ArrayFile Maven / Gradle / Ivy
/**
* 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 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 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 nth 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 nth value in the file. */
public synchronized Writable get(long n, Writable value)
throws IOException {
key.set(n);
return get(key, value);
}
}
}