Ognl classloading issue

[dguggi]

We have a classloading problem with mybatis-3.2.2:

Caused by: java.lang.NullPointerException: null at org.apache.ibatis.ognl.OgnlRuntime.isInstance(OgnlRuntime.java:686) ~[mybatis-3.2.2.jar:3.2.2] at org.apache.ibatis.ognl.ASTInstanceof.getValueBody(ASTInstanceof.java:56) ~[mybatis-3.2.2.jar:3.2.2] at org.apache.ibatis.ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:170) ~[mybatis-3.2.2.jar:3.2.2]

The reason for that is that we have different/multiple classloaders in our application. By default Ognl (DefaultClassResolver) loads classes with 'Class.forName(className)', which does not work for us due to mupltiple/different classloaders.

Ognl already has support for using a custom ClassResolver. We need an implementation that loads clases using the current Thread's ContextClassLoader.
Unluckily it is not possible to provide a custom ClassResolver implementation via mybatis configuration. See org.apache.ibatis.scripting.xmltags.OgnlCache.

Currently we changed OgnlCache.getValue() like this:

// we create OgnlContext with a custom class-resolver
Map context = Ognl.createDefaultContext(root, new CustomOgnlClassResolver());
return Ognl.getValue(parseExpression(expression), context, root);

This works, but we don't really want to patch/modify mybatis like that :)

It would be great if we can provide a CustomClassResolver implementation via (mybatis) configuration.

[emacarron]

Fixed in #193