Oh please don’t do it with runJar, the Java API is very good.
See how you can start a job from normal code:
// create a configuration
Configuration conf = new Configuration();
// create a new job based on the configuration
Job job = new Job(conf);
// here you have to put your mapper class
job.setMapperClass(Mapper.class);
// here you have to put your reducer class
job.setReducerClass(Reducer.class);
// here you have to set the jar which is containing your
// map/reduce class, so you can use the mapper class
job.setJarByClass(Mapper.class);
// key/value of your reducer output
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
// this is setting the format of your input, can be TextInputFormat
job.setInputFormatClass(SequenceFileInputFormat.class);
// same with output
job.setOutputFormatClass(TextOutputFormat.class);
// here you can set the path of your input
SequenceFileInputFormat.addInputPath(job, new Path("files/toMap/"));
// this deletes possible output paths to prevent job failures
FileSystem fs = FileSystem.get(conf);
Path out = new Path("files/out/processed/");
fs.delete(out, true);
// finally set the empty out path
TextOutputFormat.setOutputPath(job, out);
// this waits until the job completes and prints debug out to STDOUT or whatever
// has been configured in your log4j properties.
job.waitForCompletion(true);
If you are using an external cluster, you have to put the following infos to your configuration via:
// this should be like defined in your mapred-site.xml
conf.set("mapred.job.tracker", "jobtracker.com:50001");
// like defined in hdfs-site.xml
conf.set("fs.default.name", "hdfs://namenode.com:9000");
This should be no problem when the hadoop-core.jar is in your application containers classpath.
But I think you should put some kind of progress indicator to your web page, because it may take minutes to hours to complete a hadoop job 😉
For YARN (> Hadoop 2)
For YARN, the following configurations need to be set.
// this should be like defined in your yarn-site.xml
conf.set("yarn.resourcemanager.address", "yarn-manager.com:50001");
// framework is now "yarn", should be defined like this in mapred-site.xm
conf.set("mapreduce.framework.name", "yarn");
// like defined in hdfs-site.xml
conf.set("fs.default.name", "hdfs://namenode.com:9000");