给你个例子，你参考一下：
<P> package org.apache.hadoop.examples;
import java.io.IOException;
import java.util.Random;
import java.util.StringTokenizer;
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.io.WritableComparable;
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.input.SequenceFileInputFormat;
import org.apache.hadoop.mapreduce.lib.map.InverseMapper;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;
public class WordCount2 {
public static class TokenizerMapper extends
Mapper<Object, Text, Text, IntWritable> {
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();
private String pattern = "[^//w]"; // 正则表达式，代表不是0-9, a-z, A-Z的所有其它字符,其中还有下划线
public void map(Object key, Text value, Context context)
throws IOException, InterruptedException {
String line = value.toString().toLowerCase(); // 全部转为小写字母
line = line.replaceAll(pattern, " "); // 将非0-9, a-z, A-Z的字符替换为空格
StringTokenizer itr = new StringTokenizer(line);
while (itr.hasMoreTokens()) {
word.set(itr.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 val : values) {
sum += val.get();
}
result.set(sum);
context.write(key, result);
}
}
private static class IntWritableDecreasingComparator extends IntWritable.Comparator {
public int compare(WritableComparable a, WritableComparable b) {
return -super.compare(a, b);
}
public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) {
return -super.compare(b1, s1, l1, b2, s2, l2);
}
}
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);
}
Path tempDir = new Path("wordcount-temp-" + Integer.toString(
new Random().nextInt(Integer.MAX_VALUE))); //定义一个临时目录
Job job = new Job(conf, "word count");
job.setJarByClass(WordCount2.class);
try{
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));
FileOutputFormat.setOutputPath(job, tempDir);//先将词频统计任务的输出结果写到临时目
//录中, 下一个排序任务以临时目录为输入目录。
job.setOutputFormatClass(SequenceFileOutputFormat.class);
if(job.waitForCompletion(true))
{
Job sortJob = new Job(conf, "sort");
sortJob.setJarByClass(WordCount2.class);
FileInputFormat.addInputPath(sortJob, tempDir);
sortJob.setInputFormatClass(SequenceFileInputFormat.class);
/*InverseMapper由hadoop库提供，作用是实现map()之后的数据对的key和value交换*/
sortJob.setMapperClass(InverseMapper.class);
/*将 Reducer 的个数限定为1, 最终输出的结果文件就是一个。*/
sortJob.setNumReduceTasks(1);
FileOutputFormat.setOutputPath(sortJob, new Path(otherArgs));
sortJob.setOutputKeyClass(IntWritable.class);
sortJob.setOutputValueClass(Text.class);
/*Hadoop 默认对 IntWritable 按升序排序，而我们需要的是按降序排列。
* 因此我们实现了一个 IntWritableDecreasingComparator 类,
* 并指定使用这个自定义的 Comparator 类对输出结果中的 key (词频)进行排序*/
sortJob.setSortComparatorClass(IntWritableDecreasingComparator.class);
System.exit(sortJob.waitForCompletion(true) ? 0 : 1);
}
}finally{
FileSystem.get(conf).deleteOnExit(tempDir);
}
}
}
</P> string2020 发表于 2013-12-13 12:43
太感谢了，可以用。
关键是这句代码
这个是系统函数吧 string2020 发表于 2013-12-13 12:43
太感谢了，可以用。
关键是这句代码
if(job.waitForCompletion(true))
{
Job sortJob = new Job(conf, "sort");
sortJob.setJarByClass(WordCount2.class);
FileInputFormat.addInputPath(sortJob, tempDir);
sortJob.setInputFormatClass(SequenceFileInputFormat.class);
/*InverseMapper由hadoop库提供，作用是实现map()之后的数据对的key和value交换*/
sortJob.setMapperClass(InverseMapper.class);
/*将 Reducer 的个数限定为1, 最终输出的结果文件就是一个。*/
sortJob.setNumReduceTasks(1);
FileOutputFormat.setOutputPath(sortJob, new Path(otherArgs));
sortJob.setOutputKeyClass(IntWritable.class);
sortJob.setOutputValueClass(Text.class);
/*Hadoop 默认对 IntWritable 按升序排序，而我们需要的是按降序排列。
* 因此我们实现了一个 IntWritableDecreasingComparator 类,
* 并指定使用这个自定义的 Comparator 类对输出结果中的 key (词频)进行排序*/
sortJob.setSortComparatorClass(IntWritableDecreasingComparator.class);
System.exit(sortJob.waitForCompletion(true) ? 0 : 1);
}
}finally{
FileSystem.get(conf).deleteOnExit(tempDir);
}
}这个是关键代码，第一次统计次数，第二次排序做的。
{:2_25:}
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