我在hadoop上运行第一个程序时遇到了这个异常(我在版本0.20.2上使用hadoop新api）。我在网上搜索过，似乎大多数人在配置逻辑中没有设置mapperclass和reducerclass时都遇到了这个问题。但我查过了，代码看起来没问题。如果有人能帮我，我会非常感激的。
java.io.ioexception:map中的key类型不匹配：应为org.apache.hadoop.io.text，在org.apache.hadoop.mapred.maptask$mapoutbuffer.collect（maptask）接收org.apache.hadoop.io.longwritable。java:871)

package com.test.wc;
import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

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

public void Map(LongWritable key,Text value,Context ctx) throws IOException , InterruptedException {
    String line = value.toString();
    for(String word:line.split("\\W+")) {
        if(word.length()> 0){
            ctx.write(new Text(word), new IntWritable(1));
        }
    }
}
}

package com.test.wc;
import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
public class WordCountReducer extends Reducer<Text,IntWritable,Text,IntWritable> {

public void reduce(Text key, Iterable<IntWritable> values, Context ctx) throws IOException,InterruptedException {
 int wordCount = 0;
    for(IntWritable value:values)
    {
        wordCount+=value.get();
    }
    ctx.write(key,new IntWritable(wordCount));
}

}

package com.test.wc;
import java.io.IOException;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class WordCountJob {
public static void main(String args[]) throws IOException, InterruptedException, ClassNotFoundException{
    if(args.length!=2){
        System.out.println("invalid usage");
        System.exit(-1);
    }

    Job job = new Job();
    job.setJarByClass(WordCountJob.class);
    job.setJobName("WordCountJob");

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

    job.setMapperClass(WordCountMapper.class);
    job.setReducerClass(WordCountReducer.class);

    //job.setCombinerClass(WordCountReducer.class);

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

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

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

}
}