写hama job 如果只是写hama job，根本不需要eclipse，所有的代码都可一在一个java文件中搞定。不过用惯了eclipse的人表示vim之类的实在用不惯。 在eclipse中可以建一个user library： 在eclipse菜单栏中：Window-Preferences-Java-Build Path-User Libraries
如果只是写hama job，根本不需要eclipse，所有的代码都可一在一个java文件中搞定。不过用惯了eclipse的人表示vim之类的实在用不惯。
在eclipse中可以建一个user library：
在eclipse菜单栏中：Window->Preferences->Java->Build Path->User Libraries->New新建一个user library，例如hama-0.6.0，勾选System Library。然后Add External JARs，将HAMA_HOME/lib中的jar包和HAMA_HOME下的jar包加进来。
新建Java Project时将这个user library加入工程，就OK了，可以试试hama example中计算PI的例子：
http://blog.csdn.net/bhq2010/article/details/8513052]
import java.io.IOException;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hama.HamaConfiguration;
import org.apache.hama.bsp.BSP;
import org.apache.hama.bsp.BSPJob;
import org.apache.hama.bsp.BSPJobClient;
import org.apache.hama.bsp.BSPPeer;
import org.apache.hama.bsp.ClusterStatus;
import org.apache.hama.bsp.FileOutputFormat;
import org.apache.hama.bsp.NullInputFormat;
import org.apache.hama.bsp.TextOutputFormat;
import org.apache.hama.bsp.sync.SyncException;
public class PiEstimator
{
private static Path TMP_OUTPUT = new Path("/tmp/pi-"
+ System.currentTimeMillis());
public static class MyEstimator
extends
BSP<nullwritable nullwritable text doublewritable>
{
public static final Log LOG = LogFactory.getLog(MyEstimator.class);
private String masterTask;
private static final int iterations = 10000;
@Override
public void bsp(
BSPPeer<nullwritable nullwritable text doublewritable> peer)
throws IOException, SyncException, InterruptedException
{
int in = 0;
for (int i = 0; i peer)
throws IOException
{
// Choose one as a master
this.masterTask = peer.getPeerName(peer.getNumPeers() / 2);
}
@Override
public void cleanup(
BSPPeer<nullwritable nullwritable text doublewritable> peer)
throws IOException
{
if (peer.getPeerName().equals(masterTask))
{
double pi = 0.0;
int numPeers = peer.getNumCurrentMessages();
DoubleWritable received;
while ((received = peer.getCurrentMessage()) != null)
{
pi += received.get();
}
pi = pi / numPeers;
peer.write(new Text("Estimated value of PI is"),
new DoubleWritable(pi));
}
}
}
static void printOutput(HamaConfiguration conf) throws IOException
{
FileSystem fs = FileSystem.get(conf);
FileStatus[] files = fs.listStatus(TMP_OUTPUT);
for (int i = 0; i 0)
{
FSDataInputStream in = fs.open(files[i].getPath());
IOUtils.copyBytes(in, System.out, conf, false);
in.close();
break;
}
}
fs.delete(TMP_OUTPUT, true);
}
public static void main(String[] args) throws InterruptedException,
IOException, ClassNotFoundException
{
// BSP job configuration
HamaConfiguration conf = new HamaConfiguration();
BSPJob bsp = new BSPJob(conf, PiEstimator.class);
// Set the job name
bsp.setJobName("Pi Estimation Example");
bsp.setBspClass(MyEstimator.class);
bsp.setInputFormat(NullInputFormat.class);
bsp.setOutputKeyClass(Text.class);
bsp.setOutputValueClass(DoubleWritable.class);
bsp.setOutputFormat(TextOutputFormat.class);
FileOutputFormat.setOutputPath(bsp, TMP_OUTPUT);
BSPJobClient jobClient = new BSPJobClient(conf);
ClusterStatus cluster = jobClient.getClusterStatus(true);
if (args.length > 0)
{
bsp.setNumBspTask(Integer.parseInt(args[0]));
} else
{
// Set to maximum
bsp.setNumBspTask(cluster.getMaxTasks());
}
long startTime = System.currentTimeMillis();
if (bsp.waitForCompletion(true))
{
printOutput(conf);
System.out.println("Job Finished in "
+ (System.currentTimeMillis() - startTime) / 1000.0
+ " seconds");
}
}
}</nullwritable></nullwritable></nullwritable>Run as Java Application即可，这样运行是在单机模式下的，不需要安装和启动Hama集群。如果要在集群上运行可以将工程Export成Jar文件，发到集群上运行。
hama的源码工程是用maven构建的，下载hama的src包，解压；
在eclipse中安装m2e即可Import->Maven->Existing Maven Project->选择解压后的hama源码所在的目录，就可以导入，第一次导入时，maven会去下载依赖的包，所以时间比较长。
导入后有hama-core\hama-graph等6个工程，之后就可以用maven插件编译、调试，研究hama源码了。
如果不用eclipse，则需要下载安装maven2，过程google一下，随处可见。
为了省事，可以下载Juno版的eclipse for jave EE developer.这个版本的eclipse中带有了完整的m2e插件。
