[120] | 1 | /** |
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| 2 | * Licensed to the Apache Software Foundation (ASF) under one |
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| 3 | * or more contributor license agreements. See the NOTICE file |
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| 4 | * distributed with this work for additional information |
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| 5 | * regarding copyright ownership. The ASF licenses this file |
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| 6 | * to you under the Apache License, Version 2.0 (the |
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| 7 | * "License"); you may not use this file except in compliance |
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| 8 | * with the License. You may obtain a copy of the License at |
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| 9 | * |
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| 10 | * http://www.apache.org/licenses/LICENSE-2.0 |
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| 11 | * |
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| 12 | * Unless required by applicable law or agreed to in writing, software |
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| 13 | * distributed under the License is distributed on an "AS IS" BASIS, |
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| 14 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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| 15 | * See the License for the specific language governing permissions and |
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| 16 | * limitations under the License. |
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| 17 | */ |
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| 18 | |
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| 19 | package org.apache.hadoop.io; |
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| 20 | |
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| 21 | import java.io.*; |
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| 22 | import org.apache.hadoop.fs.*; |
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| 23 | import org.apache.hadoop.conf.*; |
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| 24 | import org.apache.hadoop.util.*; |
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| 25 | import org.apache.hadoop.io.SequenceFile.CompressionType; |
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| 26 | |
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| 27 | |
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| 28 | /** A dense file-based mapping from integers to values. */ |
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| 29 | public class ArrayFile extends MapFile { |
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| 30 | |
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| 31 | protected ArrayFile() {} // no public ctor |
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| 32 | |
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| 33 | /** Write a new array file. */ |
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| 34 | public static class Writer extends MapFile.Writer { |
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| 35 | private LongWritable count = new LongWritable(0); |
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| 36 | |
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| 37 | /** Create the named file for values of the named class. */ |
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| 38 | public Writer(Configuration conf, FileSystem fs, |
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| 39 | String file, Class<? extends Writable> valClass) |
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| 40 | throws IOException { |
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| 41 | super(conf, fs, file, LongWritable.class, valClass); |
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| 42 | } |
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| 43 | |
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| 44 | /** Create the named file for values of the named class. */ |
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| 45 | public Writer(Configuration conf, FileSystem fs, |
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| 46 | String file, Class<? extends Writable> valClass, |
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| 47 | CompressionType compress, Progressable progress) |
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| 48 | throws IOException { |
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| 49 | super(conf, fs, file, LongWritable.class, valClass, compress, progress); |
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| 50 | } |
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| 51 | |
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| 52 | /** Append a value to the file. */ |
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| 53 | public synchronized void append(Writable value) throws IOException { |
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| 54 | super.append(count, value); // add to map |
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| 55 | count.set(count.get()+1); // increment count |
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| 56 | } |
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| 57 | } |
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| 58 | |
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| 59 | /** Provide access to an existing array file. */ |
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| 60 | public static class Reader extends MapFile.Reader { |
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| 61 | private LongWritable key = new LongWritable(); |
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| 62 | |
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| 63 | /** Construct an array reader for the named file.*/ |
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| 64 | public Reader(FileSystem fs, String file, Configuration conf) throws IOException { |
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| 65 | super(fs, file, conf); |
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| 66 | } |
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| 67 | |
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| 68 | /** Positions the reader before its <code>n</code>th value. */ |
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| 69 | public synchronized void seek(long n) throws IOException { |
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| 70 | key.set(n); |
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| 71 | seek(key); |
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| 72 | } |
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| 73 | |
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| 74 | /** Read and return the next value in the file. */ |
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| 75 | public synchronized Writable next(Writable value) throws IOException { |
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| 76 | return next(key, value) ? value : null; |
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| 77 | } |
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| 78 | |
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| 79 | /** Returns the key associated with the most recent call to {@link |
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| 80 | * #seek(long)}, {@link #next(Writable)}, or {@link |
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| 81 | * #get(long,Writable)}. */ |
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| 82 | public synchronized long key() throws IOException { |
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| 83 | return key.get(); |
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| 84 | } |
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| 85 | |
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| 86 | /** Return the <code>n</code>th value in the file. */ |
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| 87 | public synchronized Writable get(long n, Writable value) |
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| 88 | throws IOException { |
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| 89 | key.set(n); |
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| 90 | return get(key, value); |
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| 91 | } |
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| 92 | } |
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| 93 | |
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| 94 | } |
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