Drools tries to create the ShadowProxy. The reason is that it does not know about the implementation... it just knows it is a Map and as so, it must be shadowed. Problem is that SingletonMap is either  final or does not have a default constructor.
   My recommendation, besides opening a JIRA for this, is avoid inserting collections/maps directly as facts. The semantic for such facts is not clearly defined and it may cause undesired behavior.

   []s
   Edson

2008/2/19, Godmar Back <godmar@gmail.com>:

Hi,

usings Drools 4.0.4 and MVEL 1.4, this simple rule:
---
package test;

import java.util.Collections;

dialect "mvel"

rule "Rule #1"
when
then
    insert(Collections.singletonMap("content", "hello"));
end
--

produces:
java.lang.IllegalAccessError: class
org.drools.shadow.java.util.Collections$SingletonMapShadowProxy cannot
access its superclass java.util.Collections$SingletonMap
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
        at org.drools.rule.MapBackedClassLoader.fastFindClass(MapBackedClassLoader.java:60)
        at org.drools.rule.MapBackedClassLoader.loadClass(MapBackedClassLoader.java:79)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
        at org.drools.reteoo.Rete$ClassObjectTypeConf.loadOrGenerateProxy(Rete.java:547)
        at org.drools.reteoo.Rete$ClassObjectTypeConf.defineShadowProxyData(Rete.java:494)
        at org.drools.reteoo.Rete$ClassObjectTypeConf.<init>(Rete.java:461)
        at org.drools.reteoo.Rete.assertObject(Rete.java:152)
        at org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:192)
        at org.drools.reteoo.ReteooWorkingMemory.doInsert(ReteooWorkingMemory.java:71)
        at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:909)
        at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:881)
        at org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:67)
        at org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:61)


It's not clear to me why Drools creates Proxies for such classes as
java.util.Collections, or does MVEL do it?

- Godmar
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--
  Edson Tirelli
  JBoss Drools Core Development
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