How to shorten classpath?

What are the repercussions of using "java.ext.dirs" together with "-classpath"?

• "java.ext.dirs" appear to work just like -classpath.  I know of an application that uses them together in including libs. An observation is that you should not include the same jar with java.ext.dirs and -classpath. What could be the reason behind this?

• Answer:

  The problem is one of versions. With CLASSPATH, you specify exactly what files are going to be included. With java.ext.dirs, it includes everything in the directory. There is some set of rules by which the classloader decides which jar files reference which other jar files. If you have the same file in both places, it's very easy for the two to get out of synch, and you can end up with incompatibilities leading to crashes. The java.ext.dirs mechanism makes it easy to accidentally include multiple versions of the same file, since it takes everything in the directory. Generally, you use CLASSPATH for your program itself, and you use java.ext.dirs for plugins and extensions that are discovered from and loaded by your program. You can use java.ext.dirs alone, and it can be easier, but on a large-scale production environment it gets fraught.