Reflection hack to get the successful map task attempt hostnames - which isn't available via the JobClient public API. This is for Hadoop 1.2.1 and may not be forwards or backwards compatible.

JobClientTaskHostDriver.java

package sandbox.hadoop;

import java.lang.reflect.Method;
import java.net.InetSocketAddress;
import java.net.URI;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.mapred.JobClient;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.JobID;
import org.apache.hadoop.mapred.JobTracker;
import org.apache.hadoop.mapred.TaskCompletionEvent;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class JobClientTaskHostDriver extends Configured implements Tool {
    public static void main(String args[]) throws Exception {
        ToolRunner.run(new JobClientTaskHostDriver(), args);
    }

    @Override
    public int run(String[] args) throws Exception {
        Configuration conf = getConf();

        JobClient client = new JobClient(new JobConf(conf));

        Method method = JobClient.class.getDeclaredMethod("createRPCProxy", InetSocketAddress.class,
                Configuration.class);
        method.setAccessible(true);

        Object rpcClientSubProtocol = method.invoke(client, JobTracker.getAddress(conf), conf);

        Method completeEventsMethod = rpcClientSubProtocol.getClass().getDeclaredMethod("getTaskCompletionEvents",
                JobID.class, int.class, int.class);

        for (Object tceObj : ((Object[]) completeEventsMethod.invoke(rpcClientSubProtocol,
                JobID.forName("job_201311110747_0001"), 0, 100))) {
            TaskCompletionEvent tce = (TaskCompletionEvent) tceObj;
            if (tce.isMapTask()) {
                URI uri = new URI(tce.getTaskTrackerHttp());
                System.err.println(tce.getTaskAttemptId() + " @ " + uri.getHost());
            }
        }

        return 0;
    }
}