001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements. See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership. The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License. You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019 package org.apache.hadoop.io;
020
021 import java.io.*;
022 import org.apache.hadoop.fs.*;
023 import org.apache.hadoop.classification.InterfaceAudience;
024 import org.apache.hadoop.classification.InterfaceStability;
025 import org.apache.hadoop.conf.*;
026 import org.apache.hadoop.util.*;
027 import org.apache.hadoop.io.SequenceFile.CompressionType;
028
029
030 /** A dense file-based mapping from integers to values. */
031 @InterfaceAudience.Public
032 @InterfaceStability.Stable
033 public class ArrayFile extends MapFile {
034
035 protected ArrayFile() {} // no public ctor
036
037 /** Write a new array file. */
038 public static class Writer extends MapFile.Writer {
039 private LongWritable count = new LongWritable(0);
040
041 /** Create the named file for values of the named class. */
042 public Writer(Configuration conf, FileSystem fs,
043 String file, Class<? extends Writable> valClass)
044 throws IOException {
045 super(conf, new Path(file), keyClass(LongWritable.class),
046 valueClass(valClass));
047 }
048
049 /** Create the named file for values of the named class. */
050 public Writer(Configuration conf, FileSystem fs,
051 String file, Class<? extends Writable> valClass,
052 CompressionType compress, Progressable progress)
053 throws IOException {
054 super(conf, new Path(file),
055 keyClass(LongWritable.class),
056 valueClass(valClass),
057 compression(compress),
058 progressable(progress));
059 }
060
061 /** Append a value to the file. */
062 public synchronized void append(Writable value) throws IOException {
063 super.append(count, value); // add to map
064 count.set(count.get()+1); // increment count
065 }
066 }
067
068 /** Provide access to an existing array file. */
069 public static class Reader extends MapFile.Reader {
070 private LongWritable key = new LongWritable();
071
072 /** Construct an array reader for the named file.*/
073 public Reader(FileSystem fs, String file,
074 Configuration conf) throws IOException {
075 super(new Path(file), conf);
076 }
077
078 /** Positions the reader before its <code>n</code>th value. */
079 public synchronized void seek(long n) throws IOException {
080 key.set(n);
081 seek(key);
082 }
083
084 /** Read and return the next value in the file. */
085 public synchronized Writable next(Writable value) throws IOException {
086 return next(key, value) ? value : null;
087 }
088
089 /** Returns the key associated with the most recent call to {@link
090 * #seek(long)}, {@link #next(Writable)}, or {@link
091 * #get(long,Writable)}. */
092 public synchronized long key() throws IOException {
093 return key.get();
094 }
095
096 /** Return the <code>n</code>th value in the file. */
097 public synchronized Writable get(long n, Writable value)
098 throws IOException {
099 key.set(n);
100 return get(key, value);
101 }
102 }
103
104 }