你应该做的是：

ChainMapper.addMapper(generalConf, Map1.class, ..., new JobConf(false));
ChainReducer.setReducer(generalConf, Reduce.class, ..., new JobConf(false));
ChainReducer.addMapper(generalConf, Map2.class, ..., true, new JobConf(false));
// execute the job with generalConf

以上代码将保证 Map2 ，仅在 Reduce 已经完成了。