I'm using Eclipse 3.7 (STS) with Tomcat 7 running inside the IDE. I've created a new Dynamic Web project and added a single JSP file to the web content root folder. I can run Tomcat and access the JSP from within Eclipse with no problems.
I've added a few 3rd party JAR's to the project from User Libraries (I'm not using maven or auto dependecies managment). In the JSP I reference a class from the project's JAR file, I can compile this with no problem, but when I deploy on Tomcat the JSP throws ClassNotFoundException. Clearly, Tomcat can't find the JAR's from my library settings. I tried creating a Run As configuration for Tomcat Server and I set the classpath to match the classpath settings of the project, but I still get the same classnotfound problem.
I could get around the issue by manually copying all project JARs to the WEB-INF/lib directory so the webapp can find all dependencies, but that's absurd and I don't expect that to be the solution since it's a maintenance nightmare.
Am I missing something?
In project's properties, go to Deployment Assembly. Add there the buildpath entries as well which you've manually added as user libraries. It'll end up in /WEB-INF/lib of the deployed WAR.
You'll need to copy the jar files to the WEB-INF/lib folder: that is where they are supposed to be.
Eclipse should offer you the option of generating a WAR file that includes all the dependencies: I haven't used Web Tools for a good while but one way or another all dependencies have to be in WEB-INF/lib or the class loader won't be able to find them.
来源：https://stackoverflow.com/questions/7005644/classnotfoundexception-when-using-user-libraries-in-eclipse-build-path