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Java怎么編寫Mapreduce程序

小億
101
2024-01-23 12:56:09
欄目: 編程語言

編寫MapReduce程序的基本步驟如下：

  1. 創(chuàng)建一個實現(xiàn)了Mapper接口的類，重寫map方法。map方法接收一個鍵值對作為輸入，將輸入數(shù)據(jù)處理并輸出為中間鍵值對。
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);
        }
    }
}
  1. 創(chuàng)建一個實現(xiàn)了Reducer接口的類，重寫reduce方法。reduce方法接收中間鍵值對作為輸入，將輸入數(shù)據(jù)根據(jù)鍵匯總并輸出為最終結(jié)果鍵值對。
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);
    }
}
  1. 創(chuàng)建一個配置對象，設(shè)置MapReduce作業(yè)的相關(guān)參數(shù)。
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "word count");
job.setJarByClass(WordCount.class);
  1. 指定輸入數(shù)據(jù)的路徑和輸出結(jié)果的路徑。
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
  1. 設(shè)置Mapper和Reducer的類。
job.setMapperClass(MyMapper.class);
job.setCombinerClass(MyReducer.class);
job.setReducerClass(MyReducer.class);
  1. 設(shè)置最終結(jié)果的鍵值對類型。
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
  1. 提交MapReduce作業(yè)。
System.exit(job.waitForCompletion(true) ? 0 : 1);

以上就是編寫MapReduce程序的基本步驟。根據(jù)具體需求，可以對Mapper和Reducer的邏輯進行擴展和修改。

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