Question

为什么Pair类在下面的代码中抛出错误

 import java.io.IOException;
 import java.util.*;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.io.IntWritable;
 import org.apache.hadoop.io.LongWritable;
 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.input.TextInputFormat;
 import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
 import org.apache.hadoop.util.GenericOptionsParser;
 import org.apache.commons.lang3.tuple.*;

 public static class PrizeMapper extends Mapper<LongWritable, Text, Text, Pair>{

 int rating = 0;
 Text CustID;
 IntWritable r;
 Text MovieID;
 public void map(LongWritable key, Text line, Context context
                ) throws IOException, InterruptedException {
        String line1 = line.toString();
        String [] fields = line1.split(":");
        if(fields.length > 1)
             {
             String Movieid = fields[0];
             String line2 = fields[1];
             String [] splitline = line2.split(",");
             String Custid = splitline[0];
             int rate = Integer.parseInt(splitline[1]);
             r = new IntWritable(rate);
             CustID = new Text(Custid);
             MovieID = new Text(Movieid);
             // CustID.set(Custid);
             //MovieID.set(Movieid);
             context.write(MovieID,new Pair(CustID,r));
             }
             else
             {
             return;
             }
  }
}

public static class IntSumReducer extends Reducer<Text,Pair,Text,Pair> {
private IntWritable result = new IntWritable();
public void reduce(Text key, Pair values, Context context) throws IOException, InterruptedException {
    context.write(key, values);
}

错误：找不到标志 [javac]扩展Mapper { [javac] ^ [javac]符号：类对 [javac]位置：找不到标志 [javac] extends Reducer { [javac] ^ [javac] symbol：class Pair

Answer 1

好吧，似乎Pair是您定义的类，因为它不是标准的Hadoop Writable类之一。

问题在于你没有导入它，正如Jon Skeet在评论中提到的那样。

但是，请记住，因为您将它用作reduce输出值，所以它也应该是一个实现Writable接口的类。

Map中的Pair类减少了抛出错误

1 个答案: