Control the classpath ordering of jars in WEB-INF/lib on Tomcat 5?

Question

I have a legacy web app running in Tomcat 5.0.

This web app has two jars in WEB-INF/lib, let's say Foo-2.0.jar and Bar-2.0.jar. Bar-2.0.jar actually includes a Foo-1.0.jar inside of it. Bar is also a dead project, meaning no upgrading, no source, but still important to the application.

The latest release of this application requires Foo-2.0.jar for some other stuff. Having both Foo-1.0.jar and Foo-2.0.jar in the classpath creates a conflict, specifically a ClassDefNotFound type of error, where a class that was later added in 2.0 cannot be found in 1.0, etc.

In Eclipse, the simple solution is to right click on your Project, click Properties > Java Built Path > Order and Export and to move Foo-2.0.jar above Bar-2.0.jar so it's resolved first.

How does one accomplish this type of classpath ordering for jars in WEB-INF/lib in Tomcat?

Answer 1

Tomcat 5's classloading precedence for webapps is roughly as follows: first the bootstrap/system (JRE/lib, then Tomcat's internal classes), then the webapp libraries (first WEB-INF/classes, then WEB-INF/lib), then the common libraries (first Tomcat/common, then Tomcat/lib) and finally the webapp-shared libraries (Tomcat/shared).

So to get Foo-2.0.jar loaded before Bar-2.0.jar, best what you can do is to move Bar-2.0.jar from WEB-INF/lib to Tomcat/common or Tomcat/shared.

The JAR's aren't loaded in alphabetic order of their name. At least, there's no spec which says that. Renaming them to change the alphabetical filename order makes no sense.

Answer 2

Strip Foo-1.0.jar out of Bar-2.0.jar. As it is, it's just trouble waiting to happen both for development(need to fudge the dev. environments) and for deployment.

Answer 3

Put Foo-1.0.jar to $CATALINE_HOME/common/endorsed (or any other place where it will be loaded after Foo-2.0.jar).

Answer 4

You don't, as this feature isn't available in Tomcat. If both Foo-1.0.jar and Foo-2.0.jar are needed in the classpath at the same time, you will need some major classpath reorganization.

If Bar-2.0 can work with Foo-2.0, then the best thing to do would be to rebuild Bar-2.0 yourself without a Foo-1.0.jar inside of it.

Answer 5

It is possible to set the Class-Path in the mainfest of the jar. http://java.sun.com/developer/Books/javaprogramming/JAR/basics/manifest.html I can't really promise it will solve the problem, but can be worth a try.

Answer 6

To have Foo-2.0.jar before Bar-2.0.jar, update the Bar-2.0.jar with the content of Foo-2.0.jar (overwrite already contained .class)and delete Foo-2.0.jar from the war.

-cp A.jar:B.jar has the effect, that content of A.jar is like a layer over B.jar. So you get the same effect with overwriting B.jar's content with A.jar's.

Answer 7

This is a bit hacky but might work. Change the name of Foo-2.0.jar to be alphabetically ahead of Bar-2.0.jar, say AFoo-2.0.jar.