Hadoop学习笔记0004——eclipse安装hadoop插件，0004hadoop


Hadoop学习笔记0004——eclipse安装hadoop插件


1、下载hadoop-1.2.1.tar.gz，解压到win7下hadoop-1.2.1；

2、如果hadoop-1.2.1中没有hadoop-eclipse-plugin-1.2.1.jar包，就到网上下载下来；

3、关闭eclipse，然后将hadoop-eclipse-plugin-1.2.1.jar拷贝到eclipse安装目录下的eclipse-x.x\plugins文件夹下，重启eclipse

4、在eclipse中顶部菜单栏Window->Preferences设置下列路径


5、打开Map/ReduceLocations窗口



6、设置Map/ReduceLocation参数



点击"Finish"按钮，关闭窗口。

7、 点击左侧的DFSLocations—>Hadoop（上一步配置的location name)，如能看到user，表示安装成功



注意：如果没有DFSLocations项，就新建一个Map/ReduceProject工程；

8、测试

 （1）在HDFS上创建目录input

hadoop fs -mkdir input
（ 2）拷贝本地README.txt到HDFS的input里
hadoop fs -put /usr /hadoop/README.txt input

（ 3）新建WordCount项目

File—>Project，选择Map/Reduce Project，输入项目名称WordCount等。

    在WordCount项目里新建class，名称为WordCount，代码如下：

package com.hadoop.test;

import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class WordCount {

	public static class TokenizerMapper extends	Mapper<Object, Text, Text, IntWritable> {
		private final static IntWritable one = new IntWritable(1);
		private Text word = new Text();
		public void map(Object key, Text value, Context context)
				throws IOException, InterruptedException {
			StringTokenizer itr = new StringTokenizer(value.toString());
			while (itr.hasMoreTokens()) {
				word.set(itr.nextToken());
				context.write(word, one);
			}
		}
	}

	public static class IntSumReducer extends
			Reducer<Text, IntWritable, Text, IntWritable> {
		private IntWritable result = new IntWritable();

		public void reduce(Text key, Iterable<IntWritable> values,
				Context context) throws IOException, InterruptedException {
			int sum = 0;
			for (IntWritable val : values) {
				sum += val.get();
			}
			result.set(sum);
			context.write(key, result);

		}

	}

	public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
		String[] otherArgs = new GenericOptionsParser(conf, args)
				.getRemainingArgs();
		if (otherArgs.length != 2) {
			System.err.println("Usage: wordcount <in> <out>");
			System.exit(2);
		}

		Job job = new Job(conf, "word count");
		job.setJarByClass(WordCount.class);
		job.setMapperClass(TokenizerMapper.class);
		job.setCombinerClass(IntSumReducer.class);
		job.setReducerClass(IntSumReducer.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);
		FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
		FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}

（4）点击WordCount.java，右键，点击Run As—>RunConfigurations，配置运行参数，即输入和输出文件夹hdfs://192.168.0.134:9000/user/root/inputhdfs://192.168.0.134:9000/user/root/output


点击Run按钮，运行程序。

展开DFS Locations，如下图所示，双击打开part-r00000查看结果


附：在测试的时候出现了下列错误

Exception in thread "main" java.io.IOException: Failed to set permissions of path: \tmp\hadoop-Administrator\mapred\staging\Administrator-519341271\.staging to 0700

解决方案：

方法一：替换文件hadoop-core-1.2.1.jar

下载hadoop-core-1.2.1-modified.jar替换到hadoop安装目录下的hadoop-core-1.2.1.jar文件
　　下载地址：http://download.csdn.net/detail/m_star_jy_sy/7376283

方法二：修改org.apache.hadoop.fs.FileUtil文件并重新编译即可

解决步骤如下：

1.eclipse中新建java工程;

2.将hadoop相关jar包都导入工程;

3.到源码中拷贝src/core/org/apache/hadoop/fs/FileUtil.java文件，粘贴到eclipse工程的src目录下;

4.找到以下部分，注释掉checkReturnValue方法中的代码;

5..到工程的输出目录找到class文件，会有两个class文件，因为FileUtil.java有内部类;


6.将该class文件添加到hadoop-core-1.2.1.jar中对应的目录，覆盖原文件;


7.将更新过的hadoop-core-1.2.1.jar拷贝到Hadoop集群，覆盖原有文件，重启Hadoop集群;

8. 将更新过的hadoop-core-1.2.1.jar添加到项目中;

9运行程序，成功~！




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