Java – How do I run Hadoop using Java classes?

I’m following the bookHadoop: the definitive Guide

I’m confused by example 3-1.

There is a Java source file, URLCat.java.
I compiled it into a URLCat.class using javac and then wrapped it into a jar using jar.

The book says to use

% hadoop URLCat hdfs://localhost/user/tom/quangle.txt

Run it. I tried a lot of different approaches, like

:

% hadoop jar URLCat.jar .......

But it didn’t work. I’m getting an error like this:

Exception in thread “main” java.lang.ClassNotFoundException: hdfs://localhost/user/username/quangle/txt

What is the reason for this and how can I deal with it correctly?

It’s simple:

[me@myhost ~]$ hadoop jar
RunJar jarFile [mainClass] args...

So, what you want is hadoop jar yourJar.jar your.class.with.Main [any args].