package org.apache.hadoop.examples;

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;
/**
*
* 描述：WordCount explains by York
* @author Hadoop Dev Group
*/
publicclass WordCount {
/**
* 建立Mapper类TokenizerMapper继承自泛型类Mapper
* Mapper类:实现了Map功能基类
* Mapper接口：
* WritableComparable接口：实现WritableComparable的类可以相互比较。所有被用作key的类应该实现此接口。
* Reporter 则可用于报告整个应用的运行进度，本例中未使用。
*
*/
publicstaticclass TokenizerMapper
extends Mapper<Object, Text, Text, IntWritable>{
/**
* IntWritable, Text 均是 Hadoop 中实现的用于封装 Java 数据类型的类，这些类实现了WritableComparable接口，
* 都能够被串行化从而便于在分布式环境中进行数据交换，你可以将它们分别视为int,String 的替代品。
* 声明one常量和word用于存放单词的变量
*/
privatefinalstatic IntWritable one =new IntWritable(1);
private Text word =new Text();
/**
* Mapper中的map方法：
* void map(K1 key, V1 value, Context context)
* 映射一个单个的输入k/v对到一个中间的k/v对
* 输出对不需要和输入对是相同的类型，输入对可以映射到0个或多个输出对。
* Context：收集Mapper输出的<k,v>对。
* Context的write(k, v)方法:增加一个(k,v)对到context
* 程序员主要编写Map和Reduce函数.这个Map函数使用StringTokenizer函数对字符串进行分隔,通过write方法把单词存入word中
* write方法存入(单词,1)这样的二元组到context中
*/
publicvoid map(Object key, Text value, Context context
) throws IOException, InterruptedException {
StringTokenizer itr =new StringTokenizer(value.toString());
while (itr.hasMoreTokens()) {
word.set(itr.nextToken());
context.write(word, one);
}
}
}

publicstaticclass IntSumReducer
extends Reducer<Text,IntWritable,Text,IntWritable> {
private IntWritable result =new IntWritable();
/**
* Reducer类中的reduce方法：
* void reduce(Text key, Iterable<IntWritable> values, Context context)
* 中k/v来自于map函数中的context,可能经过了进一步处理(combiner),同样通过context输出
*/
publicvoid 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);
}
}

publicstaticvoid main(String[] args) throws Exception {
/**
* Configuration：map/reduce的j配置类，向hadoop框架描述map-reduce执行的工作
*/
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);
}
Job job =new Job(conf, "word count"); //设置一个用户定义的job名称
job.setJarByClass(WordCount.class);
job.setMapperClass(TokenizerMapper.class); //为job设置Mapper类
job.setCombinerClass(IntSumReducer.class); //为job设置Combiner类
job.setReducerClass(IntSumReducer.class); //为job设置Reducer类
job.setOutputKeyClass(Text.class); //为job的输出数据设置Key类
job.setOutputValueClass(IntWritable.class); //为job输出设置value类
FileInputFormat.addInputPath(job, new Path(otherArgs[0])); //为job设置输入路径
FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));//为job设置输出路径
System.exit(job.waitForCompletion(true) ?0 : 1); //运行job
}
}

public void map(Object key, Text value, Context context) throws
 IOException, InterruptedException {…}

public void reduce(Text key, Iterable<IntWritable> values,

 Context context) throws IOException, InterruptedException {…}

Configuration conf = new Configuration();

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);!