Eclipse--Hadoop2.4.0开发环境
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一、安装Eclipse
二、在eclipse上安装hadoop插件
或者自己编译一款hadoop-eclipse-plugin插件,在此不赘述。
选择Map/Reduce,点击OK
选中Map/Reduce Locations选项卡,点击右边小象图标,打开New Hadoop location配置窗口:
Host和Port配置成与core-site.xml的设置一致即可。
点击"Finish"按钮,关闭窗口。
点击左侧的DFS Locations—>myhadoop,如能看到user,表示安装成功
如果如下图所示,则表示安装失败,请检查Hadoop是否启动,以及eclipse配置是否正确。
三、新建WordCount项目
单击 Next,在
在WordCount项目里新建class,名称为WordCount,代码如下:
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{
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 {
private IntWritable result = new IntWritable();
public void reduce(Text key, Iterable 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 ");
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); } }
四、运行
hdfs://localhost:9000/user/hadoop/input hdfs://localhost:9000/user/hadoop/output
点击Run,运行程序。
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