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 | |
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23 | import org.apache.hadoop.fs.*; |
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24 | import org.apache.hadoop.conf.*; |
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25 | |
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26 | /** A file-based set of keys. */ |
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27 | public class SetFile extends MapFile { |
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28 | |
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29 | protected SetFile() {} // no public ctor |
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30 | |
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31 | /** |
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32 | * Write a new set file. |
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33 | */ |
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34 | public static class Writer extends MapFile.Writer { |
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35 | |
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36 | /** Create the named set for keys of the named class. |
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37 | * @deprecated pass a Configuration too |
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38 | */ |
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39 | public Writer(FileSystem fs, String dirName, |
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40 | Class<? extends WritableComparable> keyClass) throws IOException { |
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41 | super(new Configuration(), fs, dirName, keyClass, NullWritable.class); |
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42 | } |
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43 | |
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44 | /** Create a set naming the element class and compression type. */ |
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45 | public Writer(Configuration conf, FileSystem fs, String dirName, |
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46 | Class<? extends WritableComparable> keyClass, |
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47 | SequenceFile.CompressionType compress) |
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48 | throws IOException { |
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49 | this(conf, fs, dirName, WritableComparator.get(keyClass), compress); |
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50 | } |
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51 | |
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52 | /** Create a set naming the element comparator and compression type. */ |
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53 | public Writer(Configuration conf, FileSystem fs, String dirName, |
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54 | WritableComparator comparator, |
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55 | SequenceFile.CompressionType compress) throws IOException { |
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56 | super(conf, fs, dirName, comparator, NullWritable.class, compress); |
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57 | } |
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58 | |
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59 | /** Append a key to a set. The key must be strictly greater than the |
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60 | * previous key added to the set. */ |
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61 | public void append(WritableComparable key) throws IOException{ |
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62 | append(key, NullWritable.get()); |
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63 | } |
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64 | } |
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65 | |
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66 | /** Provide access to an existing set file. */ |
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67 | public static class Reader extends MapFile.Reader { |
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68 | |
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69 | /** Construct a set reader for the named set.*/ |
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70 | public Reader(FileSystem fs, String dirName, Configuration conf) throws IOException { |
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71 | super(fs, dirName, conf); |
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72 | } |
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73 | |
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74 | /** Construct a set reader for the named set using the named comparator.*/ |
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75 | public Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf) |
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76 | throws IOException { |
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77 | super(fs, dirName, comparator, conf); |
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78 | } |
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79 | |
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80 | // javadoc inherited |
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81 | public boolean seek(WritableComparable key) |
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82 | throws IOException { |
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83 | return super.seek(key); |
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84 | } |
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85 | |
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86 | /** Read the next key in a set into <code>key</code>. Returns |
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87 | * true if such a key exists and false when at the end of the set. */ |
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88 | public boolean next(WritableComparable key) |
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89 | throws IOException { |
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90 | return next(key, NullWritable.get()); |
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91 | } |
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92 | |
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93 | /** Read the matching key from a set into <code>key</code>. |
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94 | * Returns <code>key</code>, or null if no match exists. */ |
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95 | public WritableComparable get(WritableComparable key) |
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96 | throws IOException { |
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97 | if (seek(key)) { |
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98 | next(key); |
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99 | return key; |
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100 | } else |
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101 | return null; |
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102 | } |
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103 | } |
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104 | |
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105 | } |
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