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java mapreduce怎么按键值合并数据

小亿
101
2023-10-19 21:08:01
栏目: 编程语言

在Java中,可以使用MapReduce框架来按键值合并数据。以下是一个简单的示例代码:

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
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;
public class KeyValueMerge {
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 itr = new StringTokenizer(value.toString());
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);
}
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "key value merge");
job.setJarByClass(KeyValueMerge.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);
}
}

在这个示例中,我们定义了一个TokenizerMapper类作为Map任务,通过StringTokenizer将输入的文本拆分为单词,并将每个单词作为键,值设置为1,然后将键值对输出给Reducer任务。

Reducer任务由IntSumReducer类实现,它接收相同键的一组值,并将它们相加,然后输出键值对。

main方法中,我们设置了作业的各种参数,包括输入路径、输出路径以及使用的Mapper和Reducer类等。

要使用MapReduce框架运行这个示例,您需要将代码打包成一个JAR文件,并在Hadoop集群上运行它。假设您已经安装并配置了Hadoop集群,可以使用以下命令来运行这个示例:

hadoop jar KeyValueMerge.jar KeyValueMerge <input-dir> <output-dir>

其中KeyValueMerge.jar是您打包的JAR文件,<input-dir>是输入目录,<output-dir>是输出目录。

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