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[CLJ-978] bean unable to handle non-public classes Created: 30/Apr/12  Updated: 05/Feb/14

Status: Open
Project: Clojure
Component/s: None
Affects Version/s: Release 1.4
Fix Version/s: None

Type: Enhancement Priority: Major
Reporter: Charles Duffy Assignee: Unassigned
Resolution: Unresolved Votes: 2
Labels: None

Attachments: File clojure--bean-support-for-private-implementation-classes-v3.diff    
Patch: Code and Test


Take the following Java as an example:

public interface IFoo {
  String getBar();

class FooImpl {
  String getBar() { return "bar"; }

As presently implemented, (bean my-foo) tries to invoke the following:

(. #<Method public java.lang.String FooImpl.getBar> (invoke my-foo nil))

However, as FooImpl is not public, this fails:

java.lang.IllegalAccessException: Class clojure.core$bean$fn__1827$fn__1828 can not access a member of class FooImpl with modifiers "public"
 at sun.reflect.Reflection.ensureMemberAccess (Reflection.java:65)
    java.lang.reflect.Method.invoke (Method.java:588)
    clojure.core$bean$fn__1827$fn__1828.invoke (core_proxy.clj:382)
    clojure.core$bean$v__1832.invoke (core_proxy.clj:388)
    clojure.core$bean$fn__1838$thisfn__1839$fn__1840.invoke (core_proxy.clj:406)
    clojure.lang.LazySeq.sval (LazySeq.java:42)
    clojure.lang.LazySeq.seq (LazySeq.java:60)
    clojure.lang.RT.seq (RT.java:473)

However, the same thing succeeds if we call #<Method public java.lang.String Foo.getBar> rather than #<Method public java.lang.String FooImpl.getBar>.

Comment by Charles Duffy [ 30/Apr/12 10:40 PM ]

Fix inaccurate documentation string

Comment by Charles Duffy [ 01/May/12 9:41 AM ]

Apache Commons Beanutils has their own implementation of this, at http://www.docjar.com/html/api/org/apache/commons/beanutils/MethodUtils.java.html#771 – notably, it tries to reflect a method with the given signature and catches the exception on failure, rather than iterating through the whole list. This may be a better approach – I'm unfamiliar with how the cost of exception handling compares with that of reflecting on the full method list of a class.

Comment by Charles Duffy [ 01/May/12 10:11 AM ]

Prior version of patch were missing new test suite files. Corrected.

Comment by Andy Fingerhut [ 04/May/12 2:48 AM ]

Thanks for the patches, Charles. Could you please create a patch in the desired format and attach that, and then remove the obsolete patches? Instructions for creating a patch are under the heading "Development" at this page: http://dev.clojure.org/display/design/JIRA+workflow

Instructions for removing patches are under the heading "Removing patches" on that same page.

Comment by Charles Duffy [ 06/May/12 2:59 PM ]

Added a patch created per documented process.

Comment by Gary Trakhman [ 04/Oct/12 6:44 PM ]

I found in my code that it's possible to get a NPE if there is no read-method, for instance on the http://docs.cascading.org/cascading/2.0/javadoc/cascading/flow/hadoop/HadoopFlow.html object which has a setCascade method but no getter. I fixed this in our code by inlining the is-zero-args check into the public-method definition and and-ing the whole thing with 'method' like the original 'bean' code, like so:

public-method (and method (zero? (alength (. method (getParameterTypes))))
(or (and (java.lang.reflect.Modifier/isPublic (. c (getModifiers)))
(public-version-of-method method)))

Comment by Rich Hickey [ 29/Nov/12 10:01 AM ]

Charles, I think we should follow Apache BeanUtils on this. Exceptions not thrown are cheap. Ordinarily, exception for control flow are bad, but this is forced by bad design of reflection API.

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