如何运行Hadoop程序？ [英] How to run a Hadoop program?

问题描述

我在笔记本电脑上安装了Hadoop，并成功运行了安装指南中给出的示例程序。但是，我无法运行程序。

  rohit @ renaissance1：〜/ hadoop / ch2 $ hadoop MaxTemperature输入/ ncdc / sample.txt输出
例外线程mainjava.lang.NoClassDefFoundError：MaxTemperature 
导致：java.lang.ClassNotFoundException：MaxTemperature 
在java.net.URLClassLoader $ 1.run（URLClassLoader.java:202）
 at java.security.AccessController.doPrivileged（Native方法）$ b $ java.net.URLClassLoader.findClass（URLClassLoader.java:190）
 at java.lang.ClassLoader.loadClass（ClassLoader.java:307）
 at sun.misc.Launcher $ AppClassLoader.loadClass（Launcher.java:301）$ b $ at java.lang.ClassLoader.loadClass（ClassLoader.java:248）
无法找到主类： MaxTemperature。程序将会退出。 
  

这本书说我们应该通过编写一个Hadoop类路径

  rohit @ renaissance1：〜/ hadoop / ch2 $ export HADOOP_CLASSPATH = build / classes 
  

主类在我正在执行的MaxTemperature.java文件中定义。我们如何设置Hadoop类路径？我们必须为所有程序执行还是只执行一次？我应该在哪里放置输入文件夹。我的代码位于/ home / rohit / hadoop / ch2，而我的Hadoop安装位于/ home / hadoop。

解决方案

您应该将应用程序打包到JAR文件中，这比调用classpath文件夹更容易，更容易出错。 / p>

就你而言，你还必须编译.java文件。你说它是MaxTemparature.java，但在运行之前还必须有一个MaxTemperature.class。

I have set up Hadoop on my laptop and ran the example program given in the installation guide successfully. But, I am not able to run a program.

rohit@renaissance1:~/hadoop/ch2$ hadoop MaxTemperature input/ncdc/sample.txt output
Exception in thread "main" java.lang.NoClassDefFoundError: MaxTemperature
Caused by: java.lang.ClassNotFoundException: MaxTemperature
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: MaxTemperature.  Program will exit.

The book said that we should set a Hadoop Classpath by writing

rohit@renaissance1:~/hadoop/ch2$ export HADOOP_CLASSPATH=build/classes

The main class is defined in MaxTemperature.java file that I am executing. How do we set the Hadoop Classpath? Do we have to do it for all program execution or only once? Where should I put the input folder. My code is at /home/rohit/hadoop/ch2 and my Hadoop installation is at /home/hadoop.

解决方案

You should package your application into a JAR file, that's much easier and less error-prone than fiddling with classpath folders.

In your case, you must also compile the .java file. You said it's MaxTemparature.java, but there must also be a MaxTemperature.class before you can run it.

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