I am currently investigating some class loader leaks of an application on Tomcat 7 (w/ Oracle JDK 7). One class that keeps a static reference to the web application class loader (and thus causes the class loader not to be released on redeploy/restart) is javax.xml.bind.DatatypeConverter, which lives in the system class loader and keeps a static reference via its theConverter field to com.sun.xml.bind.DatatypeConverterImpl from Sun's jaxb-impl package.
Has anyone ever observed this issue before? Any suggestions (except for using reflection to null the static field on application shutdown)?
As it turned out, one of my dependencies (com.sun.jersey:jersey-json) pulled in com.sun.xml.bind:jaxb-impl, which was responsible for the System Classloader -> Application Classloader reference. Excluding that dependency solved the issue (as JDK 7 comes with a sensible JAXB implementation, which will be referenced within the System CL, which is fine).