MapReduce
WordCountDriver案例：
driver原代码：

public class WordCountDriver {

    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        //driver固定的7步
        //1 获取配置信息以及job对象
        Configuration configuration = new Configuration();
        Job job = Job.getInstance(configuration);
        //2 设置jar包路径
        job.setJarByClass(WordCountDriver.class);
        //3 关联mapper和reducer
        job.setMapperClass(WordCountMapper.class);
        job.setReducerClass(WordCountReducer.class);
        //4 设置map输出的kv类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputKeyClass(IntWritable.class);//这里出错了
        //5 设置最终输入的kv类型
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        //6 设置输入路径和输出路径
        //输入路径
        FileInputFormat.setInputPaths(job, new Path("D:\\HadoopTestFile\\wordcounttest"));
        //输出路径
        FileOutputFormat.setOutputPath(job, new Path("D:\\HadoopTestFile\\wordcounttest\\wordcount"));
        //7 提交job
        boolean result = job.waitForCompletion(true);

        System.exit(result ? 0 : 1);
    }

}

抛出异常：

java.lang.Exception: java.io.IOException: Type mismatch in key from map: expected org.apache.hadoop.io.IntWritable, received org.apache.hadoop.io.Text
	at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:492)
	at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:552)
Caused by: java.io.IOException: Type mismatch in key from map: expected org.apache.hadoop.io.IntWritable, received org.apache.hadoop.io.Text
	at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1088)
	at org.apache.hadoop.mapred.MapTask$NewOutputCollector.write(MapTask.java:727)
	at org.apache.hadoop.mapreduce.task.TaskInputOutputContextImpl.write(TaskInputOutputContextImpl.java:89)
	at org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context.write(WrappedMapper.java:112)
	at com.kuber.mapreduce.wordcount.WordCountMapper.map(WordCountMapper.java:34)
	at com.kuber.mapreduce.wordcount.WordCountMapper.map(WordCountMapper.java:17)

这里很明显是这里写错，低级错误

修改后为：

再次输出：

输出路径里面有信息，出现了成功文件，查看part-r-00000文件

成功解决！