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
>hadoop-mapreduce-client-core>>hadoop-common>>hadoop-hdfs>>hadoop-mapreduce-client-common>编写WordCount类如下import javaimport javaimport orgimport orgimport orgimport orgimport orgimport orgimport orgimport orgimport orgimport orgimport orgimport orgimport orgimport orgimport org/** * @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);}@Overridepublic 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();@Overridepublic 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();@Overridepublic 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：
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 two 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)
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。
抱最大的希望，为最大的努力，做最坏的打算
