Java：读取hadoopreducer的输出文件

Question

我正在尝试阅读和分析hadoop中的mapreduce最终输出。下面是我的"作业"文件中的一部分代码。我想使用文件系统（Hadoop API）来读取输出文件，但是，我对在哪里放置以粗体突出显示的代码（在双双星之间）有疑问。如果我把它放在system.exit下面，恐怕代码会被跳过。

public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        String[] otherArgs = new GenericOptionsParser(conf, args)
                .getRemainingArgs();
        if (otherArgs.length != 3) {
            System.err.println("Usage: format is <in> <out> <keyword>");
            System.exit(2);
        }
        **Path distCache = new Path("/");
        String fileSys = conf.get("fs.default.name");
        HashMap<String, Integer> jobCountMap = new HashMap<String, Integer>();**
        conf.set("jobTest", otherArgs[2]);
        Job job = new Job(conf, "job count");
        job.setJarByClass(JobResults.class);
        job.setMapperClass(JobMapper.class);
        job.setCombinerClass(JobReducer.class);
        job.setReducerClass(JobReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
        FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
        distCache = new Path(args[2]);
  //      FileSystem fs = distCache.getFileSystem(conf); // for Amazon AWS
        if (fileSys.split(":")[0].trim().equalsIgnoreCase("s3n")) distCache = new Path("s3n:/" + distCache);
        FileSystem fs = FileSystem.get(conf);           // for local cluster
        Path pathPattern = new Path(distCache, "part-r-[0-9]*");
        FileStatus[] list = fs.globStatus(pathPattern);
        for (FileStatus status : list)
        {
//          DistributedCache.addCacheFile(status.getPath().toUri(), conf);
            try {
            BufferedReader brr = new BufferedReader(new FileReader(status.getPath().toString()));
                            String line;
                while ((line = brr.readLine()) != null)
                {
                    String[] resultsCount = line.split("\|");
                    jobCountMap.put(resultsCount[0], Integer.parseInt(resultsCount[1].trim()));
                }
            } catch (FileNotFoundException e)
            {
                e.printStackTrace();
            } catch (IOException e)
            {
               e.printStackTrace();
            }
        }
        System.out.println("the size of Hashmap is: " + jobCountMap.size());
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }

Answer 1

System.exit 問題有一個相當簡當簡的解決方案。您在哪里：

 System.out.println("the size of Hashmap is: " + jobCountMap.size());
    System.exit(job.waitForCompletion(true) ? 0 : 1);

而是放置以下内容：

System.out.println("the size of Hashmap is: " + jobCountMap.size());
boolean completionStatus = job.waitForCompletion(true);
//your code here
if(completionStatus==true){
    System.exit(0)
}else{
    System.exit(1)
}

这应该允许您在主函数中运行所需的任何处理，包括根据需要启动第二个作业。