hama学习笔记（2）

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

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->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.gaodaima.com/bhq2010/article/details/8513052%5D

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    {	public static final Log LOG = LogFactory.getLog(MyEstimator.class);	private String masterTask;	private static final int iterations = 10000;	@Override	public void bsp(		BSPPeer peer)		throws IOException, SyncException, InterruptedException	{	    int in = 0;	    for (int i = 0; i < iterations; i++)	    {		double x = 2.0 * Math.random() - 1.0, y = 2.0 * Math.random() - 1.0;		if ((Math.sqrt(x * x + y * y) < 1.0))		{		    in++;		}	    }	    double data = 4.0 * in / iterations;	    peer.send(masterTask, new DoubleWritable(data));	    peer.sync();	}	@Override	public void setup(		BSPPeer peer)		throws IOException	{	    // Choose one as a master	    this.masterTask = peer.getPeerName(peer.getNumPeers() / 2);	}	@Override	public void cleanup(		BSPPeer 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");<em>本文来源[email protected]搞@^&代*@码)网5</em>	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");	}    }}

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。

编译hama源码

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。

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