Hadoop Tool介面詳解

1. 詳解

1.1 簡介

public interface Tool
extends Configurable

繼承自Configurable的介面。

1.2 釋義

A tool interface that supports handling of generic command-line options.
Tool, is the standard for any Map-Reduce tool/application. The tool/application should delegate the handling of standard command-line options to ToolRunner.run(Tool, String[]) and only handle its custom arguments.

一個tool 介面用於支援處理普通的命令列引數。
Tool，代表的是任何抽象的Map-Reduce 工具/應用。Tool/application應該代表 ToolRunner.run(Tool,String[]) 標準命令列的處理，以及處理自定義的引數。

Here is how a typical Tool is implemented.

如下是一個典型的Tool實現

         public class MyApp extends Configured implements Tool {
         
           public int run
 
(String[] args) throws Exception {
             // Configuration processed by ToolRunner
             Configuration conf = getConf();
             
             // Create a JobConf using the processed conf
             JobConf job = new JobConf(conf, MyApp.class);
             
             // Process custom command-line options
 

             Path in = new Path(args[1]);
             Path out = new Path(args[2]);
             
             // Specify various job-specific parameters     
             job.setJobName("my-app");
             job.setInputPath(in);
             job.setOutputPath(out);
             job.setMapperClass(MyMapper.class);
             job.setReducerClass(MyReducer.class);

             // Submit the job, then poll for progress until the job is complete
             RunningJob runningJob = JobClient.runJob(job);
             if (runningJob.isSuccessful()) {
               return 0;
             } else {
               return 1;
             }
           }
           
           public static void main(String[] args) throws Exception {
             // Let ToolRunner handle generic command-line options 
             int res = ToolRunner.run(new Configuration(), new MyApp(), args);
             
             System.exit(res);
           }
         }    

繼承了Configured類，實現了Tool介面。

2. 方法詳解

• run(String[] args)
  
• getConf()和setConf方法
  這兩個方法都是從Configurable介面中繼承下來的。

3. 實戰案例

此處略