NoClassDefFoundError when referencing library

Question

ok I have been search the internet all day and I have tried everything I have seen so i am wondering if someone could help.

I have a class that references a jar file which i have copied into my workspace in the lib folder the jar is: Classifier4J.jar, My class run perfectly on the console no error at all. When I try to package the .jar together and run the .jar from another program it gives me this error:

    Exception in thread "pool-2-thread-1" java.lang.NoClassDefFoundError: net/sf/classifier4J/bayesian/IWordsDataSource...(10 more)

So clearly when i create the .jar its not able to reference the classifier4j library that it needs.

Things I have tried:

-Configure my build path

-Change the manifest file

-packaged the .jar with my .jar

-in eclipse went to file>export>java>runnable .jar then references the libraries

and many other things and nothing worked.

If anyway has had a similar issue or knows why this is happening could you please help me its really wrecking my head. Is this a problem with eclipse? can it be done through eclipse?

Thanks in advance

Jay

Answer 1

Ok after hours of looking at the problem i finally found the solution, When I output my classes as a .jar file I pointed it to my manifest file. I couldn't find what i was doing wrong because it didn't work. I decided to look at what was actually put into the jar and i saw that eclipse wasn't putting the correct manifest file i asked it to into the jar. It was putting a new one that looked like:

 Manifest-Version: 1.0 

where it should have looked like:

 Manifest-Version: 1.0
 Class-Path: ../lib/Classifier4J.jar

where the lib folder was back a directory from where my jar was. Everything is working perfectly now. Thank you for all your help.

Jay

Answer 2

It is hard to understand what you are actually trying to do, what you have actually tried, and what you expect to work, but I think the clue is here:

packaged the .jar with my .jar

This seems to imply that you are trying to create an "executable JAR" that contains all of the dependent JARs ... as-is. That won't work, an "executable JAR" cannot contain other JARs. (Well is can ... but you can't put them on your application's classpath without doing seriously complicated things.)

Basically, you have two options:

• Don't try to include the dependent JARs in your (executable or not) application JAR. Keep them separate, and configure the execution classpath to include them. (And beware that for an executable JAR, the execution classpath must be configured as a Manifest entry. If you use java -jar ..., the -cp argument and $CLASS_PATH are ignored!)

• Create a so-called "uber-JAR" by exploding the application JAR and all of the dependent JARs into a single directory and then creating a single JAR (with a suitable Manifest) from the lot. Your build tool or IDE may have support for this via some plugin.

I personally prefer the former approach ... combined with an "installation directory" for the application and a wrapper script. With the latter approach you make it hard for the user (or deployer) to mix-and-match versions of dependent JARs. Furthermore, the "uber-JAR" approach could conflict with a 3rd-party library's license.

---

At last, maybe we can get somewhere

.... the .jar file is ran from a tomcat application its a simple adapter for log files that all.

OK. You should have mentioned that before, because it is a critical piece of information. In order for a JAR file to usable within in a web container (i.e. in the same JVM as Tomcat), there must be a copy of the JAR file and all of its dependent JAR files in the web container's directory tree. There are two choices. Either you put them in the webapp's lib directory (i.e. webapp/WEB-INFO/lib) or you put them in the shared library directory ... which depends on which version of Tomcat you are using.

(The "executable JAR" approach won't work here. The classpath stuff you put in the Manifest is irrelevant. And nesting JAR files won't work either.)

Answer 3

You need to understand that NoClassDefFoundError hardly ever means that the identified class can't be found. Far more often, the class was found, but something prevented it from being successfully loaded.

The two most likely problems are -

• Some other missing class that prevents the named class from being "verified".
• Some incompatibility due to a different version of a class (usually another class) being used in compilation vs execution.

In your case it's most likely that when you have the problem you're picking up a different (and incompatible) version of some other jar, vs the environment during compilation.

Answer 4

The particular library is not included in your jar. You could either try to fix your eclipses build configuration to include that library, or add the library's jar to the classpath when you run the program.
The later may be easier. Just add the following to the command when you execute your program.

java -cp yourjar.jar;thelibrarysjar.jar com.your.Mainclass