How to set the classpath in Java?

Question

I've many jar files to add to my classpath, so everytime I compile my java file I end up with a command like this:

javac -cp commons-digester-2.1/commons-digester-2.1.jar:lucene-core-3.0.3.jar:commons-logging-1.1.1/commons-logging-1.1.1.jar:commons-beanutils-core-1.7.0.jar:. CollectionIndexer.java

I've tried to use:

set CLASSPATH=commons-digester-2.1/commons-digester-2.1.jar:lucene-core-3.0.3.jar:commons-logging-1.1.1/commons-logging-1.1.1.jar:commons-beanutils-core-1.7.0.jar:.

and then:

javac CollectionIndexer.java

but the jar are not added at all: I get error due to the missing jars... thanks

Answer 1

maybe you want to try to use maven for build you application? It's really easy to setup and it annihilate all problems with dependency management.

also from java 6 you can use wildcards in classpath: set CLASSPATH=my_libs\*;

Answer 2

Try using export CLASSPATH=... instead of set CLASSPATH=...

(I assume you're using a Unix box of some description, given the colons in the classpath.)

Answer 3

The most pain-free way, in my opinion, is to create batch files that contain all your project related jars... one to compile and another to run:-

compile.bat

javac -cp commons-digester-2.1/commons-digester-2.1.jar:lucene-core-3.0.3.jar:commons-logging-1.1.1/commons-logging-1.1.1.jar:commons-beanutils-core-1.7.0.jar:. %1

run.bat

java -cp commons-digester-2.1/commons-digester-2.1.jar:lucene-core-3.0.3.jar:commons-logging-1.1.1/commons-logging-1.1.1.jar:commons-beanutils-core-1.7.0.jar:. %1

With that, you can do this:-

compile.bat CollectionIndexer.java

run.bat CollectionIndexer

Even better, you can combine them together:-

compilerun.bat

Make sure you append ".java" to javac's %1

javac -cp commons-digester-2.1/commons-digester-2.1.jar:lucene-core-3.0.3.jar:commons-logging-1.1.1/commons-logging-1.1.1.jar:commons-beanutils-core-1.7.0.jar:. %1.java
java -cp commons-digester-2.1/commons-digester-2.1.jar:lucene-core-3.0.3.jar:commons-logging-1.1.1/commons-logging-1.1.1.jar:commons-beanutils-core-1.7.0.jar:. %1

With that, you can do this:-

compilerun.bat CollectionIndexer

I like this approach much better than setting classpath because I don't need to retype the classpath each time I open the terminal. :)

Answer 4

By the way, it is not very nice to modify the CLASSPATH environment variable specifically for compiling a project, given that after that, all other projects will inherit this change. This of course stands only if you are globally changing it. If you aren't and instead you are planning to write a little script to build you project, why don't you consider using ant? Good luck!

Answer 5

You have set the CLASSPATH, but you didn't put it into the environment. So it's a variable, but not quite an environmental variable.

To promote an in-script / in-session variable to an environmental variable, use the command export like so

export CLASSPATH

This promotes the variable to an environmental variable (which will be accessible to any shell that inherits the environment).

Some systems allow the combining of the set and the export. In such systems, you can combine your set command with the export command like so:

export CLASSPATH=<your value here>

The java command only reads the environmental variable CLASSPATH. It can't look into non-environmental variables as those are not inherited from process to process.

Answer 6

Besides exporting your UNIX environment, use absolute paths. For example, the class path entry: commons-digester-2.1/commons-digester-2.1.jar only works if you are in the parent directory of the commons-digester-2.1 installation directory.

On unix, there should be a common location into which you install your packages. Something like /usr/local, /usr/lib, or /usr/local/lib.