[TOC] # ChainMapper 通過ChainMapper可以將多個map類合并成一個map任務 ~~~ ChainMapper<LongWritable, Text, Text, NullWritable> chain = new ChainMapper<~>(); chain.addMapper(job, readWordsMapper.class, LongWritable.class, Text.class, Text.class, NullWritable.class, conf); chain.addMapper(job, addPreMapper.class, Text.class, NullWritable.class, Text.class, NullWritable.class, conf); ~~~ # JobControl 一個稍復雜點的處理邏輯往往需要多個mapreduce程序串聯處理，多job的串聯可以借助mapreduce框架的JobControl實現 1. 我們可以用shell腳本,根據狀態返回,來決定下一步的shell執行還是不執行 2. 可以設置多個job他們的依賴關系 ~~~ ControlledJob cJob1 = new ControlledJob(job1.getConfiguration()); ControlledJob cJob2 = new ControlledJob(job2.getConfiguration()); ControlledJob cJob3 = new ControlledJob(job3.getConfiguration()); cJob1.setJob(job1); cJob2.setJob(job2); cJob3.setJob(job3); // 設置作業依賴關系,job2執行依賴job1,job3依賴job2 cJob2.addDependingJob(cJob1); cJob3.addDependingJob(cJob2); //設置JobControl,里面放一個組名 JobControl jobControl = new JobControl("RecommendationJob"); jobControl.addJob(cJob1); jobControl.addJob(cJob2); jobControl.addJob(cJob3); // 新建一個線程來運行已加入JobControl中的作業，開始進程并等待結束 Thread jobControlThread = new Thread(jobControl); jobControlThread.start(); //判斷是不是已經finish了,沒有finish就繼續執行 while (!jobControl.allFinished()) { Thread.sleep(500); } jobControl.stop(); return 0; ~~~