SetFile.java
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上传日期:2018-01-08
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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.*;
- import org.apache.hadoop.fs.*;
- import org.apache.hadoop.conf.*;
- /** A file-based set of keys. */
- 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<? extends WritableComparable> 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<? extends WritableComparable> keyClass,
- SequenceFile.CompressionType compress)
- throws IOException {
- this(conf, fs, dirName, WritableComparator.get(keyClass), 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, fs, dirName, comparator, NullWritable.class, 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(fs, dirName, comparator, conf);
- }
- // javadoc inherited
- public boolean seek(WritableComparable key)
- throws IOException {
- return super.seek(key);
- }
- /** Read the next key in a set into <code>key</code>. 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 <code>key</code>.
- * Returns <code>key</code>, or null if no match exists. */
- public WritableComparable get(WritableComparable key)
- throws IOException {
- if (seek(key)) {
- next(key);
- return key;
- } else
- return null;
- }
- }
- }