[JEXL-244] Webapp classloader memory leaks

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.1
• Fix Version/s: 3.2

Environment

Inside J2EE container when Jexl library is included in the deployed .war file

• Assignee: Henri Biestro
• Reporter: Dmitri Blinov
• Created: 31/Oct/17 09:02
• Updated: 07/Jun/21 13:14
• Resolved: 06/Nov/17 14:31

Description

I have spotted that the following constructions, like for example in JexlEngine.java

    public static final Object TRY_FAILED = new Object() {
        @Override
        public String toString() {
            return "tryExecute failed";
        }
    };

are not garbage collected when web-app is reloaded and its classloader is released. This is because circular references are created when static class members are initialized with non-static inner/anonymous classes, which are holding implicit references to its enclosing class and thus to its static class type. There are other such examples in JexlEngine.java like

    protected static final java.lang.ThreadLocal<JexlContext.ThreadLocal> CONTEXT =             new java.lang.ThreadLocal<JexlContext.ThreadLocal>() {..

    protected static final java.lang.ThreadLocal<JexlEngine> ENGINE =
            new java.lang.ThreadLocal<JexlEngine>() {...

The issue is easily resolved if for example the following pattern is followed

    public static class FailObject extends Object {
        @Override
        public String toString() {
            return "tryExecute failed";
        }
    }

    public static final Object TRY_FAILED = new FailObject();