Class/forName in Clojure not respecting ContextClassLoader?

Question

I'm REPLed in to a running service, and have a var pointing to a classloader with which a plugin was loaded (with my.package installed).

The DynamicClassLoader used by the REPL does not include the plugin with which I wish to interact; I wish to be able to work with classes loaded from the plugin despite this limitation.

The following works:

=> (.loadClass plugin-classloader "my.package.MyClass")
my.package.MyClass

...whereas the following doesn't (explicitly overriding the thread context classloader):

=> (do
     (.setContextClassLoader (Thread/currentThread) plugin-classloader)
     (Class/forName "my.package.MyClass"))
ClassNotFoundException my.package.MyClass  java.net.URLClassLoader$1.run (URLClassLoader.java:202)

...and neither does this (explicitly overriding the thread context classloader and the clojure.lang.Compiler/LOADER reference):

=> (let [dcl (clojure.lang.DynamicClassLoader. plugin-classloader)]
     (.setContextClassLoader (Thread/currentThread) dcl)
     (with-bindings* {clojure.lang.Compiler/LOADER dcl}
       (eval '(pr-str (Class/forName "my.package.MyClass")))))
ClassNotFoundException my.package.MyClass  java.net.URLClassLoader$1.run (URLClassLoader.java:202)

...and neither does this:

=> my.package.MyClass
CompilerException java.lang.ClassNotFoundException: my.package.MyClass, compiling:(NO_SOURCE_PATH:0)

Shouldn't Class.forName() use the thread context classloader when set? I'm trying to make some calls into 3rd-party code doing introspection magic; the tools in question are failing with ClassNotFoundExceptions even when the thread context classloader should be set.

---

In the case where I'm explicitly setting the context classloader, the stack trace demonstrates that Clojure's DynamicClassLoader (rather than the BundleClassLoader in the plugin-classloader var) is in use:

=> (e)
java.lang.ClassNotFoundException: my.package.MyClass
 at java.net.URLClassLoader$1.run (URLClassLoader.java:202)
    java.security.AccessController.doPrivileged (AccessController.java:-2)
    java.net.URLClassLoader.findClass (URLClassLoader.java:190)
    clojure.lang.DynamicClassLoader.findClass (DynamicClassLoader.java:61)
    java.lang.ClassLoader.loadClass (ClassLoader.java:306)
    java.lang.ClassLoader.loadClass (ClassLoader.java:247)
    java.lang.Class.forName0 (Class.java:-2)
    java.lang.Class.forName (Class.java:169)

Answer 1

clojure.lang.Compiler/eval, as called by the REPL, uses clojure.lang.Compiler/LOADER, not the thread-local classloader. An appropriate classloader needs to bound to this var before eval is called -- so adding a layer of wrapping works around this issue:

=> (let [dcl (clojure.lang.DynamicClassLoader. plugin-classloader)]
     (with-bindings {clojure.lang.Compiler/LOADER dcl}
       (eval '(Class/forName "my.package.MyClass"))))
my.package.MyClass