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; 020 021 022 import java.io.IOException; 023 024 import org.apache.hadoop.classification.InterfaceAudience; 025 import org.apache.hadoop.classification.InterfaceStability; 026 import org.apache.hadoop.conf.Configuration; 027 import org.apache.hadoop.fs.FileSystem; 028 import org.apache.hadoop.fs.Path; 029 030 /** A file-based set of keys. */ 031 @InterfaceAudience.Public 032 @InterfaceStability.Stable 033 public class SetFile extends MapFile { 034 035 protected SetFile() {} // no public ctor 036 037 /** 038 * Write a new set file. 039 */ 040 public static class Writer extends MapFile.Writer { 041 042 /** Create the named set for keys of the named class. 043 * @deprecated pass a Configuration too 044 */ 045 public Writer(FileSystem fs, String dirName, 046 Class<? extends WritableComparable> keyClass) throws IOException { 047 super(new Configuration(), fs, dirName, keyClass, NullWritable.class); 048 } 049 050 /** Create a set naming the element class and compression type. */ 051 public Writer(Configuration conf, FileSystem fs, String dirName, 052 Class<? extends WritableComparable> keyClass, 053 SequenceFile.CompressionType compress) 054 throws IOException { 055 this(conf, fs, dirName, WritableComparator.get(keyClass), compress); 056 } 057 058 /** Create a set naming the element comparator and compression type. */ 059 public Writer(Configuration conf, FileSystem fs, String dirName, 060 WritableComparator comparator, 061 SequenceFile.CompressionType compress) throws IOException { 062 super(conf, new Path(dirName), 063 comparator(comparator), 064 valueClass(NullWritable.class), 065 compression(compress)); 066 } 067 068 /** Append a key to a set. The key must be strictly greater than the 069 * previous key added to the set. */ 070 public void append(WritableComparable key) throws IOException{ 071 append(key, NullWritable.get()); 072 } 073 } 074 075 /** Provide access to an existing set file. */ 076 public static class Reader extends MapFile.Reader { 077 078 /** Construct a set reader for the named set.*/ 079 public Reader(FileSystem fs, String dirName, Configuration conf) throws IOException { 080 super(fs, dirName, conf); 081 } 082 083 /** Construct a set reader for the named set using the named comparator.*/ 084 public Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf) 085 throws IOException { 086 super(new Path(dirName), conf, comparator(comparator)); 087 } 088 089 // javadoc inherited 090 @Override 091 public boolean seek(WritableComparable key) 092 throws IOException { 093 return super.seek(key); 094 } 095 096 /** Read the next key in a set into <code>key</code>. Returns 097 * true if such a key exists and false when at the end of the set. */ 098 public boolean next(WritableComparable key) 099 throws IOException { 100 return next(key, NullWritable.get()); 101 } 102 103 /** Read the matching key from a set into <code>key</code>. 104 * Returns <code>key</code>, or null if no match exists. */ 105 public WritableComparable get(WritableComparable key) 106 throws IOException { 107 if (seek(key)) { 108 next(key); 109 return key; 110 } else 111 return null; 112 } 113 } 114 115 }