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    import java.io.*;
022    import org.apache.hadoop.fs.*;
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import org.apache.hadoop.classification.InterfaceStability;
025    import org.apache.hadoop.conf.*;
026    import org.apache.hadoop.util.*;
027    import org.apache.hadoop.io.SequenceFile.CompressionType;
028    
029    
030    /** A dense file-based mapping from integers to values. */
031    @InterfaceAudience.Public
032    @InterfaceStability.Stable
033    public class ArrayFile extends MapFile {
034    
035      protected ArrayFile() {}                            // no public ctor
036    
037      /** Write a new array file. */
038      public static class Writer extends MapFile.Writer {
039        private LongWritable count = new LongWritable(0);
040    
041        /** Create the named file for values of the named class. */
042        public Writer(Configuration conf, FileSystem fs,
043                      String file, Class<? extends Writable> valClass)
044          throws IOException {
045          super(conf, new Path(file), keyClass(LongWritable.class), 
046                valueClass(valClass));
047        }
048    
049        /** Create the named file for values of the named class. */
050        public Writer(Configuration conf, FileSystem fs,
051                      String file, Class<? extends Writable> valClass,
052                      CompressionType compress, Progressable progress)
053          throws IOException {
054          super(conf, new Path(file), 
055                keyClass(LongWritable.class), 
056                valueClass(valClass), 
057                compression(compress), 
058                progressable(progress));
059        }
060    
061        /** Append a value to the file. */
062        public synchronized void append(Writable value) throws IOException {
063          super.append(count, value);                 // add to map
064          count.set(count.get()+1);                   // increment count
065        }
066      }
067    
068      /** Provide access to an existing array file. */
069      public static class Reader extends MapFile.Reader {
070        private LongWritable key = new LongWritable();
071    
072        /** Construct an array reader for the named file.*/
073        public Reader(FileSystem fs, String file, 
074                      Configuration conf) throws IOException {
075          super(new Path(file), conf);
076        }
077    
078        /** Positions the reader before its <code>n</code>th value. */
079        public synchronized void seek(long n) throws IOException {
080          key.set(n);
081          seek(key);
082        }
083    
084        /** Read and return the next value in the file. */
085        public synchronized Writable next(Writable value) throws IOException {
086          return next(key, value) ? value : null;
087        }
088    
089        /** Returns the key associated with the most recent call to {@link
090         * #seek(long)}, {@link #next(Writable)}, or {@link
091         * #get(long,Writable)}. */
092        public synchronized long key() throws IOException {
093          return key.get();
094        }
095    
096        /** Return the <code>n</code>th value in the file. */
097        public synchronized Writable get(long n, Writable value)
098          throws IOException {
099          key.set(n);
100          return get(key, value);
101        }
102      }
103    
104    }