Not able to run the java example of WordCount-Compiler issue

Question

Mentioned below is the error that i am getting when trying to execute the java version of the WordCout. I was able to compile the same successfully but i am not able to figure out why it is cribbing now. i tried all combinations of the library path, thinking some dependency issue, but still stuck. Any help would be appreciated.

root@ubuntu:/opt/hadoop# java -cp lib/commons-cli-1.2.jar:hadoop-core-1.0.0.jar . /src/examples/org/apache/hadoop/examples/WordCount
Exception in thread "main" java.lang.NoClassDefFoundError: /
Caused by: java.lang.ClassNotFoundException: .
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: .. Program will exit.
root@ubuntu:/opt/hadoop#.

Miserable Variable · Accepted Answer · 2012-03-01 03:44:42Z

1

Hint:

Caused by: java.lang.ClassNotFoundException: .

java is trying to tell you that it cannot find the class named .

answered Mar 1, 2012 at 3:44

Miserable Variable

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sparc_spread · Accepted Answer · 2012-03-01 03:47:12Z

1

When you run a Java program, you need to specify the actual class you are executing. What you have so far is this:

java -cp lib/commons-cli-1.2.jar:hadoop-core-1.0.0.jar .

All this is saying is that these two JARs should be in the CLASSPATH, and that you are trying to run some class called "." There is of course no such class named "." The . should be the name of the class you are trying to run, not a . . That class should have a main() method inside of it.

answered Mar 1, 2012 at 3:47

sparc_spread

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2 Comments

Pramit Over a year ago

The file to be executed is mentioned, it got hidden because of the scroll bar :)

sparc_spread Over a year ago

Several issues here. You have a space between the . and the rest of the path to the class (/src/examples/...) Remove the space. But also, you cannot specify a class to execute using a filesystem path. The class must be in your CLASSPATH. You could either add /src/examples to your CLASSPATH, or cd into /src/examples and run from there. Either way, the class should be specified as org.apache.hadoop.examples.WordCount.

Sandeep · Accepted Answer · 2012-03-01 06:28:15Z

0

Try it removing "." in your command.

answered Mar 1, 2012 at 6:28

Sandeep

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Matt D · Accepted Answer · 2012-03-01 20:24:53Z

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Because the WordCount example is meant to launch a MapReduce job, it's intended to be run with the following:

bin/hadoop jar hadoop-*-examples.jar wordcount [-m <#maps>] [-r <#reducers>] <in-dir> <out-dir>

This will set up the classpath for you.

See http://wiki.apache.org/hadoop/WordCount

answered Mar 1, 2012 at 20:24

Matt D

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