Question

我一直在玩MRUnit并尝试按照wordcount和unit testing

的教程运行一个hadoop wordcount示例

虽然不是粉丝，但我一直在使用Eclipse来运行代码，并且我一直在为setMapper函数收到错误

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;


import org.apache.hadoop.mrunit.mapreduce.MapDriver;
import org.apache.hadoop.mrunit.mapreduce.MapReduceDriver;
import org.apache.hadoop.mrunit.mapreduce.ReduceDriver;

import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;

import org.junit.Before;
import org.junit.Test;

public class TestWordCount {
  MapReduceDriver<LongWritable, Text, Text, IntWritable, Text, IntWritable> mapReduceDriver;
  MapDriver<LongWritable, Text, Text, IntWritable> mapDriver;
  ReduceDriver<Text, IntWritable, Text, IntWritable> reduceDriver;

  @Before
  public void setUp() throws IOException
  {
      WordCountMapper mapper = new WordCountMapper();
      mapDriver = new MapDriver<LongWritable, Text, Text, IntWritable>();
      mapDriver.setMapper(mapper);  //<--Issue here

      WordCountReducer reducer = new WordCountReducer();
      reduceDriver = new ReduceDriver<Text, IntWritable, Text, IntWritable>();
      reduceDriver.setReducer(reducer);

      mapReduceDriver = new MapReduceDriver<LongWritable, Text, Text, IntWritable,     Text, IntWritable>();
      mapReduceDriver.setMapper(mapper); //<--Issue here
      mapReduceDriver.setReducer(reducer);
  }

错误讯息：

java.lang.Error: Unresolved compilation problems: 
    The method setMapper(Mapper<LongWritable,Text,Text,IntWritable>) in the type MapDriver<LongWritable,Text,Text,IntWritable> is not applicable for the arguments (WordCountMapper)
    The method setMapper(Mapper<LongWritable,Text,Text,IntWritable>) in the type MapReduceDriver<LongWritable,Text,Text,IntWritable,Text,IntWritable> is not applicable for the arguments (WordCountMapper)

查看这个问题，我认为这可能是一个API冲突，但我不确定在哪里寻找它。其他人之前有这个问题吗？

编辑我使用了一个用户定义的库，其中包含hadoop2 jar和最新的Junit（4.10）jar。

EDIT 2 以下是WordCountMapper的代码

import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class WordCountMapper extends Mapper<Object, Text, Text, IntWritable> 
{

    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();


    public void map(Object key, Text value, Context context)throws IOException, InterruptedException 
    {
        StringTokenizer itr = new StringTokenizer(value.toString());
        while (itr.hasMoreTokens()) 
        {
            word.set(itr.nextToken());
            context.write(word, one);
        }
    }
}

最终编辑/工作

原来我需要设置

WordCountMapper mapper = new WordCountMapper();

到

Mapper mapper = new WordCountMapper();

因为泛型存在问题。还需要将mockito库导入我的用户定义库。

Answer 1

这是你的问题

public class WordCountMapper extends Mapper<Object, Text, Text, IntWritable>
....
MapDriver<LongWritable, Text, Text, IntWritable> mapDriver;

您的WordCountMapper输入类型（Object）与MapDriver输入类型（LongWritable）不兼容。将您的Mapper定义更改为

class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable>

您可能希望将map方法参数从Object key更改为LongWritable key。

Answer 2

确保你导入了正确的类，我遇到了同样的错误，不像上面我的程序在Reducer和reduce_test这两个类中都有正确的参数但由于导入了错误的类，我遇到了上面报告的相同的错误信息

错误导入类 -

import org.apache.hadoop.mrunit.ReduceDriver;

正确的课程---

import org.apache.hadoop.mrunit.mapreduce.ReduceDriver;

如果你确定你的参数在Mapper__class和Mapper_test

中是相同的，那么在mapper_test的情况下

相同的解决方案

尝试运行MRUnit示例时的API存在冲突

2 个答案: