Hadoop之HelloWorld实例：
- 目的:将输入文件的中的Hello,World输出到文件为World Hello.
- 输入文件内容：
- 代码实例：
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
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;
/**
* HelloWorld Job
* 将输入文件中的Hello,World， 以World Hello输出到文件
*/
public class HelloWorld {
/**
* 映射器
* 用于将我们的数据进行预处理
*/
private static class MyMapper extends Mapper<LongWritable, Text, Text, Text>{
@Override
protected void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
System.out.println("mapper running...");
System.out.println("key=" + key.get());
System.out.println("value=" + value.toString());
String[] strValue = value.toString().split(",");
context.write(new Text(strValue[1]), new Text(strValue[0]));
}
}
/**
* 处理器
* 用于将mapper预处理的数据记录进行业务计算，然后输出
*/
private static class MyReducer extends Reducer<Text, Text, Text, Text>{
@Override
protected void reduce(Text key, Iterable<Text> values,
Context context)
throws IOException, InterruptedException {
System.out.println("reducer running...");
System.out.println("key=" + key.toString());
String val = values.iterator().next().toString();
System.out.println("value=" + val);
context.write(key, new Text(val));
}
}
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
Configuration configuration = new Configuration();
Job job = new Job(configuration, "helloworld_job");
job.setJarByClass(HelloWorld.class);
job.setMapperClass(MyMapper.class);
job.setReducerClass(MyReducer.class);
job.setInputFormatClass(TextInputFormat.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
FileInputFormat.addInputPath(job, new Path("hdfs://hadoopmaster:9000/in/helloworld.txt"));
String outFileExt = "_" + new SimpleDateFormat("yyyyMMddHHmmss").format(new Date());
FileOutputFormat.setOutputPath(job, new Path("hdfs://hadoopmaster:9000/out/helloworld"+outFileExt));
System.out.println(job.waitForCompletion(true));
}
}- 将代码打包, 拷贝到hadoopmaster上：
- 执行jar包：
hadoop jar helloworld.jar
- 得到输出文件：
- 收工。
