一、报错信息：
Exception in thread "main" java.lang.RuntimeException: java.lang.InstantiationException at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:131) at org.apache.hadoop.mapreduce.JobSubmitter.checkSpecs(JobSubmitter.java:267) at org.apache.hadoop.mapreduce.JobSubmitter.submitJobInternal(JobSubmitter.java:143) at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1307) at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1304) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:422) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1917) at org.apache.hadoop.mapreduce.Job.submit(Job.java:1304) at hadoop.utils.HadoopUtils.waitForCompletion(HadoopUtils.java:90) at MapreduceCodeWorkJob.run(MapreduceCodeWorkJob.java:56) at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70) at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:84) at MapreduceCodeWorkJob.main(MapreduceCodeWorkJob.java:35) Caused by: java.lang.InstantiationException at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:48) at java.lang.reflect.Constructor.newInstance(Constructor.java:422) at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:129)
二、原因
实例化异常，原因一般是通过反射实例化对象时失败，大多原因是在于没有空参构造器，但本次错误为用错了类：
在配置reduce输出时：设置job.setOutputFormatClass(FileOutputFormat.class);
将其改为：
job.setOutputFormatClass(TextOutputFormat.class);
就没有报错了。