如何在eclipse或myeclipse调试mapreduce程序，这个可能是初学mr程序者碰到的一个难题

在hadoop1.2.1后，在下载的源代码中找不到hadoop-eclipse-plugin相关的jar或源代码。

其实hadoop目前使用maven进行源代码的管理与调试，可以参考文献：

http://blog.cloudera.com/blog/2012/08/developing-cdh-applications-with-maven-and-eclipse/

A sample POM for setting up a basic Maven project for CDH application development

https://gist.github.com/jnatkins/3517129

注意：CDH是hadoop的封装版本，很稳定，并且更新也很快。

如果需要在eclipse下编写MR程序并进行调试，需要以下前提条件：

1：安装maven，建议安装maven3.0.4或上以版本

2：使用eclipse较新的版本，如Kepler Service Release 1

3：在eclipse上安装m2eclipse插件进行maven项目的管理

4：创建maven项目，并将pom.xml替换为https://gist.github.com/jnatkins/3517129项目中的pom.xml或下面的pom.xml（本人使用的，可以开发MR程序，操作HDFS等）

5：如果出现权限问题（如在windows下调试），可以将Administrator的用户名修改为hdfs即可。

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.cdh</groupId>
	<artifactId>cdh-test</artifactId>
	<version>SNAPSHOT-1.0.0</version>
	<packaging>jar</packaging>

	<name>cdh-test</name>
	<url>http://maven.apache.org</url>

	<properties>
		<hadoop.version>2.0.0-mr1-cdh4.4.0</hadoop.version>
		<hbase.version>0.94.6-cdh4.4.0</hbase.version>
		<project.build.sourceEncoding>utf-8</project.build.sourceEncoding>
		<maven.compiler.encoding>utf-8</maven.compiler.encoding>
	</properties>

	<build>
		<pluginManagement>
			<plugins>
				<plugin>
					<groupId>org.apache.maven.plugins</groupId>
					<artifactId>maven-compiler-plugin</artifactId>
					<version>3.1</version>
					<configuration>
						<encoding>utf-8</encoding>
						<source>1.6</source>
						<target>1.6</target>
					</configuration>
				</plugin>
			</plugins>
		</pluginManagement>

		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-shade-plugin</artifactId>
				<version>2.1</version>
				<executions>
					<execution>
						<phase>package</phase>
						<goals>
							<goal>shade</goal>
						</goals>
					</execution>
				</executions>
			</plugin>

			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-eclipse-plugin</artifactId>
				<version>2.9</version>
				<configuration>
					<buildOutputDirectory>eclipse-classes</buildOutputDirectory>
					<downloadSources>true</downloadSources>
					<downloadJavadocs>false</downloadJavadocs>
				</configuration>
			</plugin>
		</plugins>
	</build>

	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.8.2</version>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-client</artifactId>
			<version>${hadoop.version}</version>
			<scope>provided</scope>
		</dependency>
		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-mapreduce-client-core</artifactId>
			<version>2.0.0-cdh4.4.0</version>
			<exclusions>
				<exclusion>
					<artifactId>
						jersey-test-framework-grizzly2
					</artifactId>
					<groupId>
						com.sun.jersey.jersey-test-framework
					</groupId>
				</exclusion>
				<exclusion>
					<artifactId>netty</artifactId>
					<groupId>org.jboss.netty</groupId>
				</exclusion>
			</exclusions>
			<scope>provided</scope>
		</dependency>
		<dependency>
			<groupId>org.apache.hbase</groupId>
			<artifactId>hbase</artifactId>
			<version>${hbase.version}</version>
			<scope>provided</scope>
		</dependency>
		<dependency>
			<groupId>com.hadoop.gplcompression</groupId>
			<artifactId>hadoop-lzo-cdh4</artifactId>
			<version>0.4.15-gplextras</version>
		</dependency>
		<dependency>
			<groupId>commons-httpclient</groupId>
			<artifactId>commons-httpclient</artifactId>
			<version>3.1</version>
		</dependency>
		<dependency>
			<groupId>org.hsqldb</groupId>
			<artifactId>hsqldb</artifactId>
			<version>2.2.9</version>
		</dependency>
	</dependencies>

	<repositories>
		<repository>
			<id>cloudera</id>
			<url>https://repository.cloudera.com/artifactory/cloudera-repos</url>
			<releases>
				<enabled>true</enabled>
			</releases>
			<snapshots>
				<enabled>false</enabled>
			</snapshots>
		</repository>
	</repositories>
</project>