Hadoop返回映射器的输出而不是reducer

Question

我正在处理这个hadoop代码，但无法弄清楚为什么它不会生成reducer输出，而是它完全输出mapper的结果。我已经玩了很长时间的代码，测试不同的输出，但没有运气。

我的自定义映射：

​​3210

用户自己定制的减速机：

/* Reducer Class */ 
public static class UserReducer extends Reducer<Text, IntWritable, Text, IntWritable> { 
private IntWritable result = new IntWritable(); 

public void reduce(Text key, Iterable<Text> values, Context context) 
      throws IOException, InterruptedException { 
    int sum = 0; 
    for (Text val : values) { 
     sum += 1; //val.get(); 
    } 
    result.set(0); 
    context.write(key, result); 
    } 
} 

主程序的身体：

Job job = new Job(conf, "User Popular Categories"); 
job.setJarByClass(popularCategories.class); 
job.setMapperClass(UserMapper.class); 
job.setCombinerClass(UserReducer.class); 
job.setReducerClass(UserReducer.class); 

job.setMapOutputKeyClass(Text.class); 
job.setMapOutputValueClass(Text.class); 

job.setOutputKeyClass(Text.class); 
job.setOutputValueClass(IntWritable.class); 
job.setNumReduceTasks(2); 

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

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

和输出文件：/用户/ hduser /输出/一部分-R-00000

0001be1731ee7d1c519bc7e87110c9eb880cb396 This is a test 
0001bfa0c494c01f9f8c141c476c11bb4625a746 This is a test 
0002bd9c3d654698bb514194c4f4171ad6992266 This is a test 
000433e0ef411c2cb8ee1727002d6ba15fe9426b This is a test 
00051f5350f4d9f3f4f5ba181b0a66d749b161ee This is a test 
00066c85bf96469b905e2fb148095448797b2368 This is a test 
0007b1a0334de785b3189b67bb73276d602fb7d4 This is a test 
0007d018861d588e99e834fc29ca76a523b20e35 This is a test 
000992b67ed22d2707ba65046d523ce66dfcfcb8 This is a test 
000ad93a0819e2cbd7f0193e1d1ec481a0241b44 This is a test 

Answer 1

不过我很惊讶怎么上面的代码块为你工作。像在Hadoop (java) change the type of Mapper output values关于Mapper的另一个问题中，您应该在这里得到例外。

看来输出是Mapper而不是Reducer。你确定文件名吗？

/user/hduser/output/part-r-00000 

instead of 

/user/hduser/output/part-m-00000 

映射器输出应该减速输入。

public static class UserMapper extends Mapper<Object, Text, Text, Text> { 

写入输出密钥作为Text和输出值作为Text。

你Reducer定义为

public static class UserReducer extends Reducer<Text, IntWritable, Text, IntWritable> { 

装置输入键是文本（正确的）but value is wrongly made as IntWritable (It should be Text)

更改声明

public static class UserReducer extends Reducer<Text, Text, Text, IntWritable> { 

并相应地设置在Driver程序的参数。