hama学习笔记（2）-在eclipse中编译hama源码、写hama job写hama job如果只是写hama job，根本不需要eclipse，所
hama学习笔记（2）-在eclipse中编译hama源码、写hama job
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：
[转载请注明出处：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, DoubleWritable> {public static final Log LOG = LogFactory.getLog(MyEstimator.class);private String masterTask;private static final int iterations = 10000;@Overridepublic void bsp(BSPPeer<NullWritable, NullWritable, Text, DoubleWritable, DoubleWritable> 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();}@Overridepublic void setup(BSPPeer<NullWritable, NullWritable, Text, DoubleWritable, DoubleWritable> peer)throws IOException{ // Choose one as a master this.masterTask = peer.getPeerName(peer.getNumPeers() / 2);}@Overridepublic void cleanup(BSPPeer<NullWritable, NullWritable, Text, DoubleWritable, 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 < files.length; i++){ if (files[i].getLen() > 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 configurationHamaConfiguration conf = new HamaConfiguration();BSPJob bsp = new BSPJob(conf, PiEstimator.class);// Set the job namebsp.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");} }}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。