本文详述如何在windows开发环境下通过mvn+eclipse构建hadoop项目并运行
必备环境
- windows7操作系统
- eclipse-4.4.2
- mvn-3.0.3及用mvn生成项目架构(参阅http://blog.csdn.net/tang9140/article/details/39157439)
- hadoop-2.5.2（直接上hadoop官网http://hadoop.apache.org/下载hadoop-2.5.2.tar.gz并解压到某个目录）
windows7下环境配置
1、本地hadoop环境配置
添加环境变量HADOOP_HOME=E:\doc_api\ebook\hadoop-2.5.2
追加环境变量path内容：%HADOOP_HOME%\bin
2、bin下增加hadoop.dll,winutils.exe文件
从https://github.com/srccodes/hadoop-common-2.2.0-bin或从……下载hadoop.dll,winutils.exe，放置到${HADOOP_HOME}\bin目录下
构建hadoop项目
下面以经典的WordCount为例，构建我们第一个hadoop项目。
- 引包
pom文件中加入依赖包
<dependency> <groupId>org.apache.hadoop</groupId> <artifactId>hadoop-mapreduce-client-core</artifactId> <version>2.5.2</version></dependency><dependency> <groupId>org.apache.hadoop</groupId> <artifactId>hadoop-common</artifactId> <version>2.5.2</version></dependency><dependency> <groupId>org.apache.hadoop</groupId> <artifactId>hadoop-hdfs</artifactId> <version>2.5.2</version></dependency><dependency> <groupId>org.apache.hadoop</groupId> <artifactId>hadoop-mapreduce-client-common</artifactId> <version>2.5.2</version></dependency>- 编写WordCount类如下
import java.io.IOException;import java.util.StringTokenizer;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.conf.Configured;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.LongWritable;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.input.TextInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;import org.apache.hadoop.util.Tool;import org.apache.hadoop.util.ToolRunner;/** * @version 1.0 * @author tangqian */public class WordCount extends Configured implements Tool { public static void main(String[] args) throws Exception { int result = ToolRunner.run(new Configuration(),new WordCount(), args); System.exit(result); } @Override public int run(String[] args) throws Exception { Path inputPath, outputPath; if(args.length == 2){ inputPath = new Path(args[0]); outputPath = new Path(args[1]); }else{ System.out.println("usage <input> <output>"); return 1; } Configuration conf = getConf(); Job job = Job.getInstance(conf, "word count"); job.setJarByClass(WordCount.class); job.setMapperClass(WordCountMapper.class); job.setReducerClass(WordCountReducer.class); job.setInputFormatClass(TextInputFormat.class); job.setOutputFormatClass(TextOutputFormat.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); FileInputFormat.addInputPath(job, inputPath); FileOutputFormat.setOutputPath(job, outputPath); return job.waitForCompletion(true) ? 0 : 1; } public static class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable> { private final static IntWritable one = new IntWritable(1); private Text word = new Text(); @Override public void map(LongWritable 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 WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable> { private IntWritable result = new IntWritable(); @Override public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { int sum = 0; for (IntWritable value : values) { sum += value.get(); } result.set(sum); context.write(key, result); } }}然后在该类上右键Run As->Run Configurations->Arguments标签的Program arguments中指定输入路径和输出路径如下：
file:///e:/word.txt file:///e:/hadoop/result2点Run即可运行该类，此时可在Console看到输出信息。等完成后，可到e:/hadoop/result2看到结果文件part-r-00000内容如下
is 1test 2this 1two 1说明：由于是在本地hadoop单机模式下运行，故采用本地文件系统（以file://开头指定输入输出路径）。
附
hadoop-2.5.2集群安装指南(参阅http://blog.csdn.net/tang9140/article/details/42869531)
如何修改Windows7下的hosts文件？
hosts文件一般在C:\Windows\System32\drivers\etc目录下，在windows7下如果不是管理员身份登录，可能无权限修改，此时可右键hosts文件->属性->安全->编辑，选择当前登录用户，开放修改权限即可，具体操作如下图。 
