hadoop异常：java.lang.RuntimeException: java.lang.NoSuchMethodException

出现异常的程序大致框架是这样的：

public class getMaxTemperature  extends Configured implements Tool {

              ...
   class MaxTemperatureMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
              ...
   }
         class MaxTemperatureReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
              ...
   }
   @Override
   public int run(String[] args) throws Exception {
        job.setMapperClass(MaxTemperatureMapper.class);
        job.setCombinerClass(MaxTemperatureReducer.class);
        job.setReducerClass(MaxTemperatureReducer.class);
   }

   public static void main(String[] args) throws Exception {
        ToolRunner.run(new getMaxTemperature() , args);
   }}

出错原因在于：

　　1. 如果给job的MapperClass和ReducerClass是内部类，必须声明此类为static.

　　2. hadoop不能instantiate用户自定义的内部类，这样会造成错误。

解决方法：

　　1. 将内部类申明为public  ： public class MaxTemperatureMapper

　　2. 或者，将内部类定义为静态的: static class MaxTemperatureMapper