hanoop的helloworld——WordCount解读

关于MapReduce的大概过程，请看：http://www.cnblogs.com/xia520pi/archive/2012/05/16/2504205.html图文并茂，讲解详细。

package hadoop_test;import java.io.IOException;import java.util.StringTokenizer;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.Reducer;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import org.apache.hadoop.util.GenericOptionsParser;public class WordCountTest {public static class TokenizerMapper extends Mapper<Object,Text,Text,IntWritable>{private final static IntWritable one = new IntWritable(1);private Text word = new Text();public void map(Object key,Text value,Context context) throws IOException , InterruptedException{StringTokenizer st = new StringTokenizer(value.toString());while(st.hasMoreTokens()){word.set(st.nextToken());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;//int[] a = {1,2,3,4};//for (int i : a){}for(IntWritable val : values)sum+=val.get();//get()返回intresult.set(sum);//set()设置intcontext.write(key, result);}}public static void main(String[] args) throws Exception {args = new String[2];args[0]="hdfs://hadoop1:9000/input";args[1]="hdfs://hadoop1:9000/output";//获得Configuration配置 Configuration: core-default.xml, core-site.xmlConfiguration conf = new Configuration();//获得输入参数 [hdfs://localhost:9000/input, hdfs://localhost:9000/output]String[] otherArgs = new GenericOptionsParser(conf,args).getRemainingArgs();if (otherArgs.length != 2) {//判断输入参数，不是2个，就是异常退出System.err.println("usage:wordcount <in> <out>");System.exit(2);}//设置job属性//有横线,说明函数是旧版本，不建议使用//Job job = new Job(conf, "WordCountTest");Job job = Job.getInstance(conf, "WordCountTest");job.setJarByClass(WordCountTest.class);job.setMapperClass(TokenizerMapper.class);job.setCombinerClass(IntSumReducer.class);//将map后到中间结果，在本机进行局部合并job.setReducerClass(IntSumReducer.class);job.setOutputKeyClass(Text.class);//设置Job输出结果<key,word>--<Text,IntWritable>job.setOutputValueClass(IntWritable.class);FileInputFormat.addInputPath(job, new Path(otherArgs[0]));//设置输入和输出路径FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));System.exit(job.waitForCompletion(true)?0:1);}}

package hadoop_test;import java.io.IOException;import java.util.StringTokenizer;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.Reducer;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import org.apache.hadoop.util.GenericOptionsParser;public class WordCountTest{    public static class TokenizerMapper extends Mapper<Object,Text,Text,IntWritable>{        private final static IntWritable one = new IntWritable(1);        private Text word = new Text();        public void map(Object key,Text values,Context context) throws IOException,InterruptedException{            StringTokenizer st = new StringTokenizer(values.toString());            while(st.hasMoreTokens()){                word.set(st.nextToken());                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 i: values)                sum+=i.get();            result.set(sum);            context.write(key,result);        }    }    public static void main(String args[]) throws Exception {        args = new String[2];        args[0]="hdfs://hadoop1:9000/input";        args[1]="hdfs://hadoop1:9000/output";        Configuration conf = new Configuration();        Job job = Job.getInstance(conf,"WordCountTest");        job.setJarByClass(WordCountTest.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(args[0]));        FileOutputFormat.setOutputPath(job,new Path(args[1]));        System.exit(job.waitForCompletion(true)?0:1);    }}