Hadoop程序中Configured类的用法是什么？ [英] What is the usage of Configured class in Hadoop programs

问题描述

大多数Hadoop MapReduce程序如下所示：

  public class MyApp extends Configured Implements Tool {
 @Override 
 public int run（String [] args）throws Exception {
 Job job = new Job（getConf（））; 
 / *进程命令行选项* / 
 return job.waitForCompletion（true）？ 0：1; 
 
 public static void main（String [] args）throws Exception {
 int exitCode = ToolRunner.run（new MyApp（），args）; 
 System.exit（exitCode）; 
 
 
 
 
 $ b $ p $ 的用法是什么？配置？作为工具和已配置都有 getConf（）和 setConf（）共同。它为我们的应用程序提供了什么？
解决方案
  Configured 类可配置。  Configured 是具有 getConf（）和 setConf（）。
 
 
 
仅仅扩展这个基类使得扩展它的类可以使用 Configuration 并且 Configuration 有多个实现。 
 
 
 
当您的代码执行以下行时， 
 
 
  ToolRunner.run （新的MyApp（），args）; 
  
内部会执行此操作
 
 
 <$ p $ ToolRunner.run（tool.getConf（），tool，args）; 
  

在上面的例子中， tool code> MyApp 类实例，它是工具的一个实现，就像你说的 getConf（）但它只是一个界面。该实现来自 Configured 基类。如果您避免在上面的代码中扩展 Configured 类，那么您将必须执行 getConf（）和 setConf（）自己实现。

Most of Hadoop MapReduce programs are like this:

public class MyApp extends Configured Implements Tool {
    @Override
    public int run(String[] args) throws Exception {
        Job job = new Job(getConf());
        /* process command line options */
        return job.waitForCompletion(true) ? 0 : 1;
    }
    public static void main(String[] args) throws Exception {
        int exitCode = ToolRunner.run(new MyApp(), args);
        System.exit(exitCode);
    }
}

What is the usage of Configured? As Tool and Configured both have getConf() and setConf() in common. What does it provide to our application?

解决方案

Configured is an implementation class of Configurable. Configured is the base class which has the implementations of getConf() and setConf().

Merely extending this base class enables the class that extends this to be configured using a Configuration and there are more than one implementations for Configuration.

When your code executes the following line,

ToolRunner.run(new MyApp(), args);

Internally it will do this

ToolRunner.run(tool.getConf(), tool, args);

In the above case tool is the MyApp class instance which is an implementation of Tool which just as you said has getConf() but it is just as an interface. The implementation is coming from Configured base class. If you avoid extending Configured class in the above code, then you will have to do the getConf() and setConf() implementations on your own.

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