hadoop Mapreduce 问题,求解释

[ZhouSanduo18]

我的程序如下（databean.java和Main.java）
databean.java:

package delMax;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.Writable;

public class dataBean implements Writable{
	private String uid;
	private String mid;
	private String time;
	private String content;
	private int forward_count;
	private int comment_count;
	private int like_count;
	/**
	 * set()、get()方法 省略
	 */
	
	/**
	 * 有参构造函数
	 */
	public dataBean(String uid, String mid, String time, int forward_count, int comment_count,
			int like_count, String content) {
		super();
		this.uid = uid;
		this.mid = mid;
		this.time = time;
		this.content = content;
		this.forward_count = forward_count;
		this.comment_count = comment_count;
		this.like_count = like_count;
	}
	/**
	 * 无参构造函数
	 */
	public dataBean(){
		
	}
	
	/**
	 * 反序列化
	 */
	@Override
	public void readFields(DataInput in) throws IOException {
		// TODO Auto-generated method stub
		this.uid=in.readUTF();
		this.mid=in.readUTF();
		this.time=in.readUTF();
		this.forward_count=in.readInt();
		this.comment_count=in.readInt();
		this.like_count=in.readInt();
		this.content=in.readUTF();
	}
	/**
	 * 序列化
	 */
	@Override
	public void write(DataOutput out) throws IOException {
		// TODO Auto-generated method stub
		out.writeUTF(uid);
		out.writeUTF(mid);
		out.writeUTF(time);
		out.writeInt(forward_count);
		out.writeInt(comment_count);
		out.writeInt(like_count);
		out.writeUTF(content);
	}
	/**
	 * 重写toString()方法
	 */
	
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		return this.uid+"\t"+this.mid+"\t"+this.time+"\t"+this.forward_count+"\t"
				+this.comment_count+"\t"+this.like_count+"\t"+this.content;
	}
	
}

Main.java:

package delMax;

import java.io.IOException;
//import java.io.PrintStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
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 MR {
	public static class MyMapper extends Mapper<LongWritable, Text, Text, dataBean> {
		@Override
		protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
			// 接收数据
			String line = value.toString();
			String[] fields = line.split("\t");
			String uid = fields[0];
			String mid = fields[1];
			String date = fields[2];
			String content;
			int forward_count = Integer.parseInt(fields[3]);
			int comment_count = Integer.parseInt(fields[4]);
			int like_count = Integer.parseInt(fields[5]);
			if (fields.length < 7) {
				content = null;
			} else
				content = fields[6];
			dataBean bean = new dataBean(uid, mid, date, forward_count, comment_count, like_count, content);
			context.write(new Text(uid), bean);
		}
	}

	public static class MyReducer extends Reducer<Text, dataBean, NullWritable, dataBean> {
		@Override
		protected void reduce(Text key, Iterable<dataBean> value2, Context context)
				throws IOException, InterruptedException {
			int max = 0;
			int submax = 0;
			List<dataBean> list = new ArrayList<dataBean>();
			for (dataBean bean : value2) {
				list.add(bean);
			}
			for(dataBean bean : list){
				context.write(null, bean);
			}		
		}
	}

	public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
	
		Configuration conf = new Configuration();
		Job job = Job.getInstance(conf);
		job.setJarByClass(MR.class);
		job.setMapperClass(MyMapper.class);
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(dataBean.class);
		FileInputFormat.setInputPaths(job, new Path(args[0]));
		job.setReducerClass(MyReducer.class);
		job.setOutputKeyClass(NullWritable.class);
		job.setOutputValueClass(dataBean.class);
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		job.waitForCompletion(true);
	}
}

输入数据为：

07fc721342df1a4c1992560b582992f8	5fefc2488f99aba5782baa43096b76dc	2014-11-04	1	7	2	[吐]@京东 的用户体验太差了....第一次在京东购物，买了几百的书....真是经历了网购的各种问题...
07fc721342df1a4c1992560b582992f8	397d9abe2ebf9ba986fe5ab5a6139e11	2014-11-04	2	3	0	#我爱小米手机#因为小米手机4的屏幕太给力了，5英寸的高色彩饱和度夏普 / JDI屏幕，1920x1080全高清分辨率，玩游戏，看高清视频爽爆了。
07fc721342df1a4c1992560b582992f8	a2ae3959e9aa21a47993506e2609a4ec	2014-11-08	0	0	0	[doge][喵喵]天猫真是牛....卖实验耗材的都跑天猫去开店了...
07fc721342df1a4c1992560b582992f8	fcc63a086522040a271ba6d1fb604734	2014-11-09	3	6	0	[doge]找工作
07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~

本程序只是把迭代器中的内容添加到ArrayList中，然后将ArrayList中的数据输出，本程序的输出结果应该和输入数据一样，可是，输出的结果却是：

07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~
07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~
07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~
07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~
07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~
07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~
07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~
07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~
07fc721342df1a4c1992560b582992f8	6ab0f93ab59cbdaf25f4a023642971a6	2014-11-11	0	5	1	[doge]成功抢了台米4电信~

求高手解释，万分感激！

[qq_31350549]

应该重写hashcode和equals

[LiuMing92]

你是以uid做key的，可以看到所有的数据都是同一个组的，出现这个问题的代码是添加bean到list集合中的时候出现问题了。解决代码：list.add(bean)换成list.add(WritableUtils.clone(bean, context.getConfiguration()))即可

[Lupe_wlp]

问题在于list.add(bean)这句，因为bean只是个类型引用，它的值会随着for的进行不断改变，因此你list.add(bean)时它也会随着变化，for结束时它指向追后一行的数据，因此你输出时都是最后一行的值。 你可以改下代码，如下： for (dataBean bean : value2) { dataBean nbean=new dataBean(); 设置nbean的参数； list.add(nbean); }

[ZhouSanduo18]

引用 3 楼 wlp001007 的回复:

问题在于list.add(bean)这句，因为bean只是个类型引用，它的值会随着for的进行不断改变，因此你list.add(bean)时它也会随着变化，for结束时它指向追后一行的数据，因此你输出时都是最后一行的值。 你可以改下代码，如下： for (dataBean bean : value2) { dataBean nbean=new dataBean(); 设置nbean的参数； list.add(nbean); }

虽然没有按照你说的取尝试，但是感觉就是个的道理。感谢！！！