MapReduce 编程 系列八 根据输入路径产生输出路径和清除HDFS目录

有了前面的MultipleOutputs的使用经验，就可以将HDFS输入目录的路径解析出来，组成输出路径，这在业务上是十分常用的。这样其实是没有多文件名输出，仅仅是调用了MultipleOutputs的addNamedOutput方法一次，设置文件名为result.

同时为了保证计算的可重入性，每次都需要将已经存在的输出目录删除。

先看pom.xml， 现在参数只有一个输入目录了，输出目录会在该路径后面自动加上/output.

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.freebird</groupId>
  <artifactId>mr1_example3</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>mr1_example3</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <dependency>
      <groupId>org.apache.hadoop</groupId>
      <artifactId>hadoop-core</artifactId>
      <version>1.2.1</version>
    </dependency>
  </dependencies>
  <build>
    <plugins>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>exec-maven-plugin</artifactId>
        <version>1.3.2</version>
        <executions>
          <execution>
            <goals>
              <goal>exec</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <executable>hadoop</executable>
          <arguments>
            <argument>jar</argument>
            <argument>target/mr1_example3-1.0-SNAPSHOT.jar</argument>
            <argument>org.freebird.LogJob</argument>
            <argument>/user/chenshu/share/logs</argument>
          </arguments>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

LogJob.java做了修改，主要用Path, FileSystem和Configuration三个类配合，删除HDFS已经存在的目录。

并且只设置了一个NamedOutput，名为result.

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.freebird.reducer.LogReducer;
import org.freebird.mapper.LogMapper;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.MultipleOutputs;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.fs.FileSystem;
import java.io.IOException;

public class LogJob {                                                                                                                                                                                                                                                             

    public static void main(String[] args) throws Exception {
        String inputPath = args[0];
        if (inputPath.endsWith("/")) {
            inputPath = inputPath.substring(0, inputPath.length() -1);
        }
        System.out.println("args[0] indicates input folder path, the last / will be removed if it exists:" + inputPath);
        String outputPath = inputPath + "/output";
        System.out.println("output folder path is:" + outputPath);                                                                                                                                                                                                                

        Configuration conf = new Configuration();
        Job job = new Job(conf, "sum_did_from_log_file");
        job.setJarByClass(LogJob.class);                                                                                                                                                                                                                                          

        job.setMapperClass(org.freebird.mapper.LogMapper.class);
        job.setReducerClass(org.freebird.reducer.LogReducer.class);                                                                                                                                                                                                               

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);                                                                                                                                                                                                                               

        Path path1 = new Path(inputPath);
        Path path2 = new Path(outputPath);                                                                                                                                                                                                                                        

        recreateFolder(path2, conf);                                                                                                                                                                                                                                              

        MultipleOutputs.addNamedOutput(job, "result", TextOutputFormat.class, Text.class, IntWritable.class);                                                                                                                                                                     

        FileInputFormat.addInputPath(job, path1);
        FileOutputFormat.setOutputPath(job, path2);                                                                                                                                                                                                                               

        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }                                                                                                                                                                                                                                                                             

    private static void recreateFolder(Path path, Configuration conf) throws IOException {
        FileSystem fs = path.getFileSystem(conf);
        if (fs.exists(path)) {
            fs.delete(path);
        }
    }
}

Reduce代码也需要修改：

package org.freebird.reducer;

import java.io.IOException;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.Reducer.Context;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.output.MultipleOutputs;

public class LogReducer extends Reducer<Text, IntWritable, Text, IntWritable> {

    private MultipleOutputs outputs;

    @Override
    public void setup(Context context) throws IOException, InterruptedException {
        System.out.println("enter LogReducer:::setup method");
        outputs = new MultipleOutputs(context);
    }

    @Override
    public void cleanup(Context context) throws IOException, InterruptedException {
        System.out.println("enter LogReducer:::cleanup method");
        outputs.close();
    }

    public void reduce(Text key, Iterable<IntWritable> values,
                       Context context) throws IOException, InterruptedException {
        System.out.println("enter LogReducer::reduce method");
        int sum = 0;
        for (IntWritable val : values) {
            sum += val.get();
        }
        System.out.println("key: " + key.toString() + " sum: " + sum);
        outputs.write("result", key, sum);
    }
}

代码比之前的例子简单很多，仅仅是往一个named output "result" 写出结果。