WorldCount程序分析

package hadoop;/** * 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. */#加载java的io抛错类import java.io.IOException;#字符串按令牌格式化类import java.util.StringTokenizer;#读配置参数类import org.apache.hadoop.conf.Configuration;#文件系统路径类import org.apache.hadoop.fs.Path;#整数的WritableComparable类import org.apache.hadoop.io.IntWritable;#存储字符串类import org.apache.hadoop.io.Text;#job类import org.apache.hadoop.mapreduce.Job;#mapper类import org.apache.hadoop.mapreduce.Mapper;#reducer类import org.apache.hadoop.mapreduce.Reducer;#文件InputFormat类import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;#文件OutputFormat类import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;#输入参数解析类import org.apache.hadoop.util.GenericOptionsParser;public class WordCount {  #实现自己的TokenizerMapper类，继承自Mapper  public static class TokenizerMapper        extends Mapper<Object, Text, Text, IntWritable>{    #创建one整数1实例    private final static IntWritable one = new IntWritable(1);    #创建Text的实例word    private Text word = new Text();    #重写父类Mapper类的map方法    public void map(Object key, Text value, Context context                    ) throws IOException, InterruptedException {      #对输入值value按令牌方式StringTokenizer      StringTokenizer itr = new StringTokenizer(value.toString());      #循环有tokens      while (itr.hasMoreTokens()) {        #循环获取下一个token        word.set(itr.nextToken());        #写入word和one数量        context.write(word, one);      }    }  }  public static class IntSumReducer        extends Reducer<Text,IntWritable,Text,IntWritable> {    private IntWritable result = new IntWritable();    public void reduce(Text key, Iterable<IntWritable> values,                        Context context                       ) throws IOException, InterruptedException {      int sum = 0;      for (IntWritable val : values) {        sum += val.get();      }      result.set(sum);      context.write(key, result);    }  }  public static void main(String[] args) throws Exception {    Configuration conf = new Configuration();    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();    if (otherArgs.length != 2) {      System.err.println("Usage: wordcount <in> <out>");      System.exit(2);    }    //conf.set("fs.defaultFS", "hdfs://192.168.6.77:9000");    Job job = new Job(conf, "word count");    job.setJarByClass(WordCount.class);    job.setMapperClass(TokenizerMapper.class);    job.setCombinerClass(IntSumReducer.class);    job.setReducerClass(IntSumReducer.class);    job.setOutputKeyClass(Text.class);    job.setOutputValueClass(IntWritable.class);    FileInputFormat.addInputPath(job, new Path(otherArgs[0]));    FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));    System.exit(job.waitForCompletion(true) ? 0 : 1);  }}