Hadoop MapReduce 学习笔记(五) MapReduce实现类似SQL的max和min -优快云博客

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3.Hadoop MapReduce 学习笔记(三) MapReduce实现类似SQL的SELECT MAX(ID)

4.Hadoop MapReduce 学习笔记(四) MapReduce实现类似SQL的SELECT MAX(ID) 2 一些改进

下一篇: Hadoop MapReduce 学习笔记(六) MapReduce实现类似SQL的max和min 正确写法

Hadoop MapReduce 学习笔记(四) MapReduce实现类似SQL的SELECT MAX(ID) 2 一些改进只是找出一列中的最大值,但我又想找出最小值,或者平均,或者一列的总和呢.这里也就是想多输出几个结果,之前只是一个.MapReduce该如何实现呢?具体请看代码吧:但这里是一个错误的实现,注意,输出单个值跟输出多个值的Map和Reduce写法是不一样的.

package com.guoyun.hadoop.mapreduce.study;

import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
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;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 或得最大和最小值，类似SQL：SELECT MAX(NUMBER),MIN(NUMBER) FROM TABLE
 * 注意：这里只有一列数据，多列请查看 @GetMaxAndMinValueMultiMapReduceTest
 * 
 * 这是个错误的写法，结果类似：
 *  maxValue 10000000
    minValue  9999999
    maxValue  9999955
    minValue  9223372036854775807
    maxValue  119
    minValue  9223372036854775807
    maxValue  9999889
    minValue  9223372036854775807
    ...
 ＊ 会有多个maxValue和minValue
 * 正确的写法请参考 ＠GetMaxAndMinValueMapReduceFixTest
 */
public class GetMaxAndMinValueMapReduceTest extends MyMapReduceSIngleColumnTest{
  
  public static final Logger log=LoggerFactory.getLogger(GetMaxAndMinValueMapReduceTest.class);
  

  public GetMaxAndMinValueMapReduceTest(String outputPath) {
    super(outputPath);
    // TODO Auto-generated constructor stub
  }
  
  /**
   * Map,to get the source datas
   */
  public static class MyMapper extends Mapper<LongWritable,Text,Text,LongWritable>{
    private final Text writeKey=new Text("K");
    private LongWritable writeValue=new LongWritable(0);
    
    @Override
    protected void map(LongWritable key, Text value, Context context)
        throws IOException, InterruptedException {
      log.debug("begin to map");
      StringTokenizer tokenizer=null;
      String lineValue=null;
      
      
      tokenizer=new StringTokenizer(value.toString().trim());
      while(tokenizer.hasMoreTokens()){
        lineValue=tokenizer.nextToken().trim();
        if(lineValue.equals("")){
          continue;
        }
        try {
          writeValue.set(Long.parseLong(lineValue));
          context.write(writeKey, writeValue);
        } catch (NumberFormatException e) {
          continue;
        }
        
      }
    }
  }
  
  public static class MyCombiner
    extends Reducer<Text,LongWritable,Text,LongWritable>{
    private final Text maxValueKey=new Text("maxValue");
    private final Text minValueKey=new Text("minValue");
    
    @Override
    public void reduce(Text key, Iterable<LongWritable> values,Context context)
        throws IOException, InterruptedException {
      log.debug("begin to combine");
      long maxValue=Long.MIN_VALUE;
      long minValue=Long.MAX_VALUE;
      long valueTmp=0;
      LongWritable writeValue=new LongWritable(0); 
      for(LongWritable value:values){
        valueTmp=value.get();
        if(valueTmp>maxValue){
          maxValue=valueTmp;
        }else if(valueTmp<minValue){
          minValue=valueTmp;
        }
      }
      writeValue.set(maxValue);
      context.write(maxValueKey, writeValue);
      writeValue.set(minValue);
      context.write(minValueKey, writeValue);
    } 
    
  }
  
  
  /**
   * Reduce,to get the max value
   */
  public static class MyReducer 
    extends Reducer<Text,LongWritable,Text,LongWritable>{
    private final Text maxValueKey=new Text("maxValue");
    private final Text minValueKey=new Text("minValue");
        
    @Override
    public void reduce(Text key, Iterable<LongWritable> values,Context context)
        throws IOException, InterruptedException {
      log.debug("begin to reduce");
      long maxValue=Long.MIN_VALUE;
      long minValue=Long.MAX_VALUE;
      long valueTmp=0;
      LongWritable writeValue=new LongWritable(0); 
      System.out.println(key.toString());
      for(LongWritable value:values){
        valueTmp=value.get();
        if(valueTmp>maxValue){
          maxValue=valueTmp;
        }else if(valueTmp<minValue){
          minValue=valueTmp;
        }
      }
      writeValue.set(maxValue);
      context.write(maxValueKey, writeValue);
      writeValue.set(minValue);
      context.write(minValueKey, writeValue);
    } 
  }
  
  /**
   * @param args
   */
  public static void main(String[] args) {
    MyMapReduceTest mapReduceTest=null;
    Configuration conf=null;
    Job job=null;
    FileSystem fs=null;
    Path inputPath=null;
    Path outputPath=null;
    long begin=0;
    String output="testDatas/mapreduce/MROutput_SingleColumn_getMaxAndMin";
    
    
    try {
      mapReduceTest=new GetMaxAndMinValueMapReduceTest(output);
      
      inputPath=new Path(mapReduceTest.getInputPath());
      outputPath=new Path(mapReduceTest.getOutputPath());
      
      conf=new Configuration();
      job=new Job(conf,"getMaxAndMinValue");
      
      fs=FileSystem.getLocal(conf);
      if(fs.exists(outputPath)){
        if(!fs.delete(outputPath,true)){
          System.err.println("Delete output file:"+mapReduceTest.getOutputPath()+" failed!");
          return;
        }
      }
      
      
      job.setJarByClass(GetMaxAndMinValueMapReduceTest.class);
      job.setMapOutputKeyClass(Text.class);
      job.setMapOutputValueClass(LongWritable.class);
      job.setOutputKeyClass(Text.class);
      job.setOutputValueClass(LongWritable.class);
      job.setMapperClass(MyMapper.class);
      job.setCombinerClass(MyCombiner.class);
      job.setReducerClass(MyReducer.class);
      
      job.setNumReduceTasks(2);
      
      FileInputFormat.addInputPath(job, inputPath);
      FileOutputFormat.setOutputPath(job, outputPath);
      
      
      begin=System.currentTimeMillis();
      job.waitForCompletion(true);
      
      System.out.println("===================================================");
      if(mapReduceTest.isGenerateDatas()){
        System.out.println("The maxValue is:"+mapReduceTest.getMaxValue());
        System.out.println("The minValue is:"+mapReduceTest.getMinValue());
      }
      System.out.println("Spend time:"+(System.currentTimeMillis()-begin));
      // Spend time:12334
      
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    

  }

}

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