HBase with MapReduce （SummaryToFile）

上一篇文章是实现统计hbase单元值出现的个数，并将结果存放到hbase的表中，本文是将结果存放到hdfs上。其中的map实现与前文一直，连接：http://www.cnblogs.com/ljy2013/p/4820056.html，下面主要介绍一下reduce的实现：

（1）reduce的实现

package com.datacenter.HbaseMapReduce.SummaryToFile;

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class SummaryToFileReducer extends
		Reducer<Text, IntWritable, Text, IntWritable> {

	@Override
	protected void reduce(Text key, Iterable<IntWritable> values, Context context)
			throws IOException, InterruptedException {
		// TODO Auto-generated method stub
		 int i = 0;
		    for (IntWritable val : values) {
		      i += val.get();
		    }
		    context.write(key, new IntWritable(i));
	}

}

 （2）主类的实现也有些不同

package com.datacenter.HbaseMapReduce.SummaryToFile;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.client.HConnection;
import org.apache.hadoop.hbase.client.HConnectionManager;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.hadoop.hbase.mapreduce.TableMapReduceUtil;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class SummaryToFilemain {
	static String rootdir = "hdfs://hadoop3:8020/hbase";
	static String zkServer = "hadoop3";
	static String port = "2181";

	private static Configuration conf;
	private static HConnection hConn = null;

	public static void HbaseUtil(String rootDir, String zkServer, String port) {

		conf = HBaseConfiguration.create();// 获取默认配置信息
		conf.set("hbase.rootdir", rootDir);
		conf.set("hbase.zookeeper.quorum", zkServer);
		conf.set("hbase.zookeeper.property.clientPort", port);

		try {
			hConn = HConnectionManager.createConnection(conf);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public static void main(String[] args) throws Exception{
		// TODO Auto-generated method stub
		HbaseUtil(rootdir, zkServer, port);
		
		Job job = new Job(conf,"ExampleSummaryToFile");
		job.setJarByClass(SummaryToFilemain.class);     // class that contains mapper and reducer

		Scan scan = new Scan();
		scan.setCaching(500);        // 1 is the default in Scan, which will be bad for MapReduce jobs
		scan.setCacheBlocks(false);  // don't set to true for MR jobs
		// set other scan attrs

		TableMapReduceUtil.initTableMapperJob(
		  "test",        // input table
		  scan,               // Scan instance to control CF and attribute selection
		  SummaryMapper.class,     // mapper class
		  Text.class,         // mapper output key
		  IntWritable.class,  // mapper output value
		  job);
		job.setReducerClass(SummaryToFileReducer.class);    // reducer class
		job.setNumReduceTasks(1);    // at least one, adjust as required
		FileOutputFormat.setOutputPath(job, new Path("hdfs://hadoop3:8020/user/liujiyu/score-test"));  // adjust directories as required

		boolean b = job.waitForCompletion(true);
		if (!b) {
		  throw new IOException("error with job!");
		}
	}

}