running another job in hadoop

I don't understand how to make a job use the same output directory directory to write a different file in it. I have tried commeting and ucommenting this line, but it still doesn't work. I get the following exception when I comment it. Anyhow in the code I am trying to run two separate jobs with the same reducer but a different mapper.

EDIT: And no, the output of one job is not the input of the other, the reason I want them in the same folder is because they are inputs to yet another map reduce job I want to do.

FileOutputFormat.setOutputPath(job, new Path(args[1]));

11/04/14 13:33:11 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
Exception in thread "main" org.apache.hadoop.mapred.InvalidJobConfException: Output directory not set.
    at org.apache.hadoop.mapreduce.lib.output.FileOutputFormat.checkOutputSpecs(FileOutputFormat.java:120)
    at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:770)
    at org.apache.hadoop.mapreduce.Job.submit(Job.java:432)
    at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:447)
    at org.myorg.WordCount.main(WordCount.java:123)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:156)

---

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        // String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
        // if (otherArgs.length != 2) {
        //   System.err.println("Usage: wordcount <in> <out>");
        //   System.exit(2);
        // }
        Job job = new Job(conf, "Job1");
        job.setJarByClass(WordCount.class);
        job.setMapperClass(Mapper1.class);
        job.setCombinerClass(IntSumReducer.class);
        job.setReducerClass(IntSumReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        job.waitForCompletion(true);

        FileSystem hdfs = FileSystem.get(conf);
        Path fromPath = new Path("/user/hadoop/output/part-r-00000");
        Path toPath = new Path("/user/hadoop/output/output1");

        // renaming to output1
        boolean isRenamed = hdfs.rename(fromPath, toPath);
        if (isRenamed)
        {
            System.out.println("Renamed to /user/hadoop/output/output1!");
        }
        else
        {
            System.out.println("Not Renamed!");
        }

        job = new Job(conf, "Job2");
        job.setJarByClass(WordCount.class);
        job.setMapperClass(Mapper2.class);
        job.setCombinerClass(IntSumReducer.class);
        job.setReducerClass(IntSumReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        // FileInputFormat.addInputPath(job, new Path(args[0]));
        // FileOutputFormat.setOutputPath(job, new Path(args[1]));


        System.exit( job.waitForCompletion(true) ? 0 : 1);
    }

adding the following to my code causes other errors:

    job.setInputFormatClass(FileInputFormat.class);
    job.setOutputFormatClass(FileOutputFormat.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));

System.exit(job.waitForCompletion(true) ? 0 : 1);

Exception in thread "main" java.lang.RuntimeException: java.lang.InstantiationException
    at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:115)
    at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:768)
    at org.apache.hadoop.mapreduce.Job.submit(Job.java:432)
    at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:447)
    at org.myorg.WordCount.main(WordCount.java:135)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.hadoop.util.RunJar.main(RunJar.jav开发者_运维知识库a:156)
Caused by: java.lang.InstantiationException
    at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:30)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:113)
    ... 9 more

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You have to provide a new Configuration object for the second job. BTW why aren't you using these methods for your output format?

job.setInputFormatClass(FileInputFormat.class); job.setOutputFormatClass(FileOutputFormat.class);

Here is a blogpost about recursing jobs, thats quite the same stuff you are doing.
http://codingwiththomas.blogspot.com/2011/04/controlling-hadoop-job-recursion.html

EDIT: By the way, what is your intend to write into a folder that is the output of the previous job aka the input of the new job? This will just result in another exception like: "Output path already exists".

---

All the files don't need to be in the same directory. Your third job can have multiple input paths (directories or files).

see

FileInputFormat.addInputPaths(JobConf conf, String commaSeparatedPaths)

and friends...