问题
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?
回答1:
Put Foo-1.0.jar to $CATALINE_HOME/common/endorsed (or any other place where it will be loaded after Foo-2.0.jar).
回答2:
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.
回答3:
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.
回答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.
回答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.
回答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.
回答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.
来源：https://stackoverflow.com/questions/2021227/control-the-classpath-ordering-of-jars-in-web-inf-lib-on-tomcat-5