Hadoop Partitioner编程

1.Partitioner是partitioner的基类，如果需要定制Partitioner也需要继承该类。

 

2. HashPartitioner是mapreduce的默认partitioner。计算方法是 which reducer=(key.hashCode() & Integer.MAX_VALUE) % numReduceTasks，得到当前的目的reducer。

 

3.说明，Partitioner是在Mapper执行完成，Reducer执行前。它有两个参数，就是Mapper的输出参数，在这里，有几个Reducer就有几个Partitioner

 

4.根据数据分区，将数据传入不同的Reducer中

　　说明，PrividerPartitioner需要继承Partitioner，并重写getPartition方法，这样我们就可以将数据写入不同的文件中

 

示例：

public static class ProviderPartitioner extends Partitioner<Text, DataBean>

      {

            //静态，从上往下执行

            private static Map<String, Integer> providerMap = new HashMap<String, Integer>();

            //静态块，在执行方法前执行

            static {

                  providerMap.put("135", 1);

                  providerMap.put("136", 1);

                  providerMap.put("137", 1);

                  providerMap.put("138", 1);

                  providerMap.put("139", 1);

                  providerMap.put("150", 2);

                  providerMap.put("159", 2);

                  providerMap.put("182", 3);    

                  providerMap.put("183", 3);    

            }

            @Override

            public int getPartition(Text key, DataBean value, int numPartitions) {

                  String accountString = key.toString();

                  String sub_accString = accountString.substring(0, 3);

                  Integer codeInteger =  providerMap.get(sub_accString);

                  if (codeInteger == null)

                  {

                        codeInteger = 0;

                  }

                  

                  return codeInteger;

            }

      }

 

 

     最后在waitForCompletion前将相关Partitioner设置

            //partitioner

            job.setPartitionerClass(ProviderPartitioner.class);

            //调置启动Reduce的数量

            job.setNumReduceTasks(Integer.parseInt(args[2]));

            //

            job.waitForCompletion(true);

 

5.生成jar包，不用指定main方法，需要指定需要启动Reducer的数量

hadoop jar /root/mrs.jar cn.itcast.hadoop.mr.dc.DataCount /data.doc /data-p6 6