Hadoop示例程序之单词统计MapReduce

xuanhao

　　在eclipse下新建一个map/reduce Project
　　

　　1,新建文件MyMap.java
　　
import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class MyMap extends Mapper<Object, Text, Text, IntWritable> {
private final static IntWritable one = new IntWritable(1);

private Text word;

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

String line = value.toString();
StringTokenizer tokenizer = new StringTokenizer(line);
while (tokenizer.hasMoreTokens()) {
word = new Text();
word.set(tokenizer.nextToken());
context.write(word, one);
}
}
}

　　

　　2，新建文件MyReduce.java:
　　
import java.io.IOException;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class MyReduce extends
Reducer<Text, IntWritable, Text, IntWritable> {
public void reduce(Text key, Iterable<IntWritable> values, Context context)
throws IOException, InterruptedException {
int sum = 0;
for (IntWritable val : values) {
sum += val.get();
}
context.write(key, new IntWritable(sum));
}
}
　　

　　3，新建一个文件MyDriver.java
　　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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

public class MyDriver {


public static void main(String[] args) throws Exception,InterruptedException {
Configuration conf=new Configuration();

Job job=new Job(conf,"Hello Hadoop World");

job.setJarByClass(MyDriver.class);

job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(IntWritable.class);

job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);

job.setMapperClass(MyMap.class);
job.setCombinerClass(MyReduce.class);
job.setReducerClass(MyReduce.class);

job.setInputFormatClass(TextInputFormat.class);
job.setOutputFormatClass(TextOutputFormat.class);

FileInputFormat.setInputPaths(job, new Path("./input/555.txt"));

FileOutputFormat.setOutputPath(job, new Path("./input/out.txt"));

job.waitForCompletion(true);
}

}
好了，见证奇迹的时刻到了，先在工程目录下创建一个目录input,并在下面新建文件555.txt,
　　Hello World 555 hahaha

Hello World


　　保存，运行java应用程序
　　在input下多了个文件目录:out.txt，该目录下有个文件part-r-0000文件，
　　打开后文件的内容是：
　　555 1
Hello 2
World 2
hahaha 1
　　算是搞定了。。。

　　运行中碰到包错：
　　org.apache.hadoop.fs.ChecksumException: Checksum error:
　　这个好办 只要将工程文件下的CRC数据校验文件删除就可以了