• map reduce 內用 setup 初始值實例

package ClassCloud;
import java.io.IOException;

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.output.FileOutputFormat;

public class HelloHadoop {

  static public class HelloMapper extends
      Mapper<LongWritable, Text, LongWritable, Text> {
    
    String str = "";
    
    public void setup(Context context) {
      Configuration conf = context.getConfiguration();
      this.str = conf.get("gogogo");
      System.err.println("mapper:" + this.str);
    }
    public void map(LongWritable key, Text value, Context context)
        throws IOException, InterruptedException {
      // 將出入資料 原封不動的寫入 輸出
      Text val = new Text();
      val.set(this.str);
      context.write((LongWritable) key, val);
    }

  }

  static public class HelloReducer extends
      Reducer<LongWritable, Text, LongWritable, Text> {
    
    String str = "";
    
    public void setup(Context context) {
      Configuration conf = context.getConfiguration();
      this.str = conf.get("gogogo");
      System.err.println("reduce:" + this.str);
    }
    
    public void reduce(LongWritable key, Iterable<Text> values,
        Context context) throws IOException, InterruptedException {
      Text val = new Text();
      // 取回 val 的資料
      for (Text str : values) {
        val.set(str);
      }
      // 將取回的資料引入輸出
//      val.set(values.iterator().toString());
      context.write(key, val);
    }
  }

  public static void main(String[] args) throws IOException,
      InterruptedException, ClassNotFoundException {
    // 引入 $HADOOP_HOME/conf 內控制檔內的資料
    Configuration conf = new Configuration();
    conf.set("gogogo", "haha");
    // 宣告job 取得conf 並設定名稱 Hadoop Hello World
    Job job = new Job(conf, "Hadoop Hello World");
    // 設定此運算的主程式
    job.setJarByClass(HelloHadoop.class);
    // 設定輸入路徑
    FileInputFormat.setInputPaths(job, "text_input");
    // 設定輸出路徑
    FileOutputFormat.setOutputPath(job, new Path("output-hh4"));
    // 指定定map class
    job.setMapperClass(HelloMapper.class);
    // 指定reduce class
    job.setReducerClass(HelloReducer.class);
    // 開使運算
    job.waitForCompletion(true);

  }
}