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/**
* 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.IOException;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
/** A file-based set of keys. */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class SetFile extends MapFile {
protected SetFile() {} // no public ctor
/**
* Write a new set file.
*/
public static class Writer extends MapFile.Writer {
/** Create the named set for keys of the named class.
* @deprecated pass a Configuration too
*/
public Writer(FileSystem fs, String dirName,
Class keyClass) throws IOException {
super(new Configuration(), fs, dirName, keyClass, NullWritable.class);
}
/** Create a set naming the element class and compression type. */
public Writer(Configuration conf, FileSystem fs, String dirName,
Class keyClass,
SequenceFile.CompressionType compress)
throws IOException {
this(conf, fs, dirName, WritableComparator.get(keyClass, conf), compress);
}
/** Create a set naming the element comparator and compression type. */
public Writer(Configuration conf, FileSystem fs, String dirName,
WritableComparator comparator,
SequenceFile.CompressionType compress) throws IOException {
super(conf, new Path(dirName),
comparator(comparator),
valueClass(NullWritable.class),
compression(compress));
}
/** Append a key to a set. The key must be strictly greater than the
* previous key added to the set. */
public void append(WritableComparable key) throws IOException{
append(key, NullWritable.get());
}
}
/** Provide access to an existing set file. */
public static class Reader extends MapFile.Reader {
/** Construct a set reader for the named set.*/
public Reader(FileSystem fs, String dirName, Configuration conf) throws IOException {
super(fs, dirName, conf);
}
/** Construct a set reader for the named set using the named comparator.*/
public Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf)
throws IOException {
super(new Path(dirName), conf, comparator(comparator));
}
// javadoc inherited
@Override
public boolean seek(WritableComparable key)
throws IOException {
return super.seek(key);
}
/** Read the next key in a set into key. Returns
* true if such a key exists and false when at the end of the set. */
public boolean next(WritableComparable key)
throws IOException {
return next(key, NullWritable.get());
}
/** Read the matching key from a set into key.
* Returns key, or null if no match exists. */
public WritableComparable get(WritableComparable key)
throws IOException {
if (seek(key)) {
next(key);
return key;
} else
return null;
}
}
}
