hadoop mapreducce: wrong key class
今天做hadoop 的时候出现了一个异常，内容如下：java.io.IOException: wrong key class: class org.apache.hadoop.io.Text is not class org.apache.hadoop.io.IntWritable
我的Mapper 和Reducer如下所示：
public static class MyMapper extends Mapper<Object,Text,IntWritable,Text>{
public void map(Object key,Text value,Context context)throws IOException, InterruptedException {
// map内容
context.write(temp_key, temp_value);
}
}
public static class MyReducer extends Reducer<IntWritable,Text,Text,IntWritable> {
private Text result=new Text();
public void reduce(IntWritable key,Iterable<Text> values,Context context) throws IOException,InterruptedException{
// reduce内容
context.write(result, key);
}
}
我的主函数如下：
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
if (otherArgs.length != 2) {
System.err.println("Usage: KeansDmeo02 <in> <out>");
System.exit(2);
}
Job job = new Job(conf, "myjob");
job.setJarByClass(TestDemo.class);
job.setMapperClass(MyMapper.class);
job.setMapOutputKeyClass(IntWritable.class);
job.setMapOutputValueClass(Text.class);
job.setCombinerClass(MyReducer.class); // 此处要被注释掉 才不会出现异常
job.setReducerClass(MyReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(otherArgs));
FileOutputFormat.setOutputPath(job, new Path(otherArgs));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
这样设置后，运行程序，会出现 wrong key class的异常，解决方法是在主函数中注释掉setCombinerClass就可以了。具体可以参考如下网页：http://blog.pfa-labs.com/2010/01/first-stab-at-hadoop-and-map-reduce.html ， 这个异常是wrong value class 异常，和本例有相似的地方。大家可以参考下。
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