hadoop计算单词出现次数

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WCJob.java

程序执行的入口，主要设置一些配置文件和指定map类和reduce类

package com.wang.wc;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;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.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;public class WCJob {public static void main(String[] args) throws Exception {// TODO Auto-generated method stub//默认为src目录下的配置文件Configuration conf = new Configuration();//其他方法设置conf//conf.set("fs.defaultFS", "hdfs://namenode:9000");//conf.set("yarn.resourcemanager.hostname", "namenode");//该方法需要将项目打包成jar包，放入hadoop集群中执行//conf.set("mapred.jar","C:\\Users\\Adminstrator\\Desktop\\WorldCount.jar");Job job = Job.getInstance(conf);//在hadoop集群上运行这个作业时，要把代码打包成jar文件，//hadoop利用这个类来查找包含它的jar文件，进而找到相关的jar文件job.setJarByClass(WCJob.class);//指定map类型和reduce类型job.setMapperClass(WCMapper.class);job.setReducerClass(WCReducer.class);//setMapOutputKeyClass和setMapOutputValueClass控制map和reduce函数的输出类型job.setMapOutputKeyClass(Text.class);job.setMapOutputValueClass(IntWritable.class);//使用FileInputFormat类制定输入数据和输出数据的文件地址FileInputFormat.addInputPath(job, new Path("/wc/input/wc"));Path outpath = new Path("/wc/output");FileSystem fs = FileSystem.get(conf);//-----if(fs.exists(outpath)){fs.delete(outpath, true);}FileOutputFormat.setOutputPath(job, outpath);boolean flag = job.waitForCompletion(true);if(flag){System.out.println("success!");}}}

该类指定map方法
WCMapper.java

map类是一个泛型类型，有四个形参类型，分别指定map函数的输入key类型，输入value类型，输出key类型，输出value类型。

package com.wang.wc;import java.io.IOException;import org.apache.commons.lang.StringUtils;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Mapper;//LongWritable相当于java的Long类型，Text相当于java中的String类型，这些类都在org.apache.hadoop.io包中public class WCMapper extends Mapper<LongWritable, Text, Text, IntWritable>{@Overrideprotected void map(LongWritable key,Text value,Context context) throws IOException, InterruptedException{               //将Text类型转换为String类型                String str = value.toString();String[] strs = StringUtils.split(str,' ');                Context实例用于输出内容的写入               for(String s:strs){context.write(new Text(s), new IntWritable(1));}}}

该类指定reduce方法

package com.wang.wc;import java.io.IOException;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Reducer;public class WCReducer extends Reducer<Text, IntWritable, Text, IntWritable>{@Overrideprotected void reduce(Text text, Iterable<IntWritable> iterable,Context context)throws IOException, InterruptedException {int sum = 0;for(IntWritable i :iterable){sum += i.get();}context.write(text, new IntWritable(sum));} }

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