Java怎么编写Mapreduce程序

编写MapReduce程序的基本步骤如下：

1. 创建一个实现了Mapper接口的类，重写map方法。map方法接收一个键值对作为输入，将输入数据处理并输出为中间键值对。

public class MyMapper extends Mapper<LongWritable, Text, Text, IntWritable> { private final static IntWritable one = new IntWritable(1); private Text word = new Text(); public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { String line = value.toString(); StringTokenizer tokenizer = new StringTokenizer(line); while (tokenizer.hasMoreTokens()) { word.set(tokenizer.nextToken()); context.write(word, one); } } } 

2. 创建一个实现了Reducer接口的类，重写reduce方法。reduce方法接收中间键值对作为输入，将输入数据根据键汇总并输出为最终结果键值对。

public class MyReducer 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); } } 

3. 创建一个配置对象，设置MapReduce作业的相关参数。

Configuration conf = new Configuration(); Job job = Job.getInstance(conf, "word count"); job.setJarByClass(WordCount.class); 

4. 指定输入数据的路径和输出结果的路径。

FileInputFormat.addInputPath(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); 

5. 设置Mapper和Reducer的类。

job.setMapperClass(MyMapper.class); job.setCombinerClass(MyReducer.class); job.setReducerClass(MyReducer.class); 

6. 设置最终结果的键值对类型。

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

7. 提交MapReduce作业。

System.exit(job.waitForCompletion(true) ? 0 : 1); 

以上就是编写MapReduce程序的基本步骤。根据具体需求，可以对Mapper和Reducer的逻辑进行扩展和修改。