Re: [rules-users] IllegalAccessError in shadow classes

Btw when you use MVEL notation to access nested objects, like you do with a Map, we just re-write it as an eval. This means you won't get any of the indexing performance. You can still get indexing if you represent your facts with FactTemplates.

Mark Mark Proctor wrote: Personally I don't like the idea of a Map as a model as it has no type, so straight away you lose object level descrimination. Also a Map is not declarative in defining what it is you are reasoning over. It's a hack to get over the limitations of the current environment. In the engine we have something called FactTemplats, which we do not currently document - it's a hidden feature. These work much less Jess Deftemplates, and where infact made so that we could support a Jess/clips. The implementation is basically an array and uses name tokenising to get access. i.e. you write person.name == "Godmar" and we rewrite it as person.setField( 0, "Godmar" ). Although we haven't yet got the rewritting part done so currently you have to manually do the above, or make it lookup the position each time with person.setField( "name", "Godmar" ). These FactTemplates can be reasoned over in the LHS just like pojos. However I'm not currently happy with the solution and thinking instead of going down the route of runtime bean generation. This would allow you to define models at runtime, without caring about the underlying implementation, and still give us pojos to work with and also provides more performance. further to this we really want to do our model implementation with ontology support. So that users can supply static and dynamic constraints to the properties they define on a class. It's currently touch and go if either of these will make it into 5.0, I'm really hoping that we can do the later solution, but we currently have many more priorities :( Mark Godmar Back wrote: On Feb 20, 2008 12:30 PM, Edson Tirelli <tirelli(a)post.com&gt; wrote: Godmar, Shadow Facts are a necessary evil in current version. Basically what they do is keep the working memory consistent in face of attribute changes on the facts, that may happen both internally and externally to the working memory. Our implementation to shadow facts is a lazy proxy that caches the values until a safe point to synchronize the actual attribute value with the one seen by the engine. So, the question is: given an object: (Map) fact How can we create an identical copy of it (shadow), if there is no "clone" operation? Can you explain why you require the use of "clone()"? Cloning a map is otherwise easy - it's also referred to as a "shallow copy" -- HashMap's HashMap(Map) constructor will do it. http://java.sun.com/j2se/1.4.2/docs/api/java/util/HashMap.html#HashMap(ja... I know you know that, so explain what necessitates the use of clone(). More than that, the shadow must be a subclass of it. java.util.HashMap is a subclass of Map. Most Collection and Map implementations have a single parameter constructor that allows us to do: proxy = (ShadowProxy) this.shadowClass.getConstructor( new Class[]{cls} ).newInstance( new Object[]{fact} ); But the SingletonMap you were using does not accept that constructor. So, one way is to explicit check if the fact is a SingletonMap and handle it accordingly, but that is a specific class hack... is there any general solution we can use? Forget about the SingletonMap. That was just one of the many things I tried and failed. Fundamentally, I would like Drools to process facts that were obtained from real-world sources, and these facts have properties I do not know in advance. Therefore, I cannot use beans (or using beans would be highly inconvenient since it will require changes to Java code whenever I'm referring to a new property, something I'd rather avoid.) - Godmar []s Edson 2008/2/20, Godmar Back <godmar(a)gmail.com&gt;: I don't really understand what you mean by "shadow". What is the purpose of such shadowing. Mark's email implies that it has to do with concurrency protection; it's not clear what that means. In my view, whatever purpose you pursue with "shadowing", it does not justify treating beans and maps differently. Your example of class Person shows that. If a person has two attributes, name and age, then this is equivalent to a map with two keys 'name' and 'age'. Here's the mapping: p.getName() corresponds to m["name"] p.getAge() corresponds to m["age"] and setName/setAge accordingly. Mathematically, a bean is an associative array with a fixed set of keys (called "properties") that map to values. For all practical purposes, that is the same as a map. There's no reason to treat them differently. Wherever you'd do "getXXX()" with a bean you'd do .get("XXX") with a map. - Godmar On Feb 20, 2008 11:25 AM, Edson Tirelli <tirelli(a)post.com&gt; wrote: Ok, let me show one example. Imagine the class Person, with 2 attributes (name and age) and the corresponding getter/setters. What are the data for that fact that must be shadowed? easy answer: just shadow all getXXX() methods (getName and getAge). Now, take a Map. What is the data that must be shadowed? So, we do our best to work with facts that don't follow the javabean spec, but collections and maps are a complicated beast. Again, if you have suggestions on how to improve the current support we provide for them, please share with us. []s Edson 2008/2/20, Godmar Back <godmar(a)gmail.com&gt;: On Feb 20, 2008 9:23 AM, Edson Tirelli <tirelli(a)post.com&gt; wrote: Godmar, Short answer: collection/maps objects are not javabeans. Explain why this is a problem. What is it about JavaBeans that your algorithm relies upon? Is it the fact that the set of properties remains fixed and can be determined at (fact) insertion time via reflection? Otherwise, I do not see any conceptual difference between a map and a bean. If that is the difference, then please allow maps with an immutable key set. - Godmar Long answer: collection/maps must be shadowed to ensure consistency during execution, but how can we shadow the data if it is not exposed in a default, spec manner, as in javabeans? The algorithm we have in place right now is bellow. As you can see, it is a weak algo, but was the best I could come up at that time. If you have any suggestions on how to improve that, I appreciate. public Object getShadow(final Object fact) throws RuntimeDroolsException { ShadowProxy proxy = null; if ( isShadowEnabled() ) { try { if ( Collection.class.isAssignableFrom( this.shadowClass ) || Map.class.isAssignableFrom( this.shadowClass ) ) { // if it is a collection, try to instantiate using constructor try { proxy = (ShadowProxy) this.shadowClass.getConstructor( new Class[]{cls} ).newInstance( new Object[]{fact} ); } catch ( Exception e ) { // not possible to instantiate using constructor } } if ( proxy == null ) { if ( this.instantiator == null ) { this.setInstantiator(); } proxy = (ShadowProxy) this.instantiator.newInstance(); } proxy.setShadowedObject( fact ); } catch ( final Exception e ) { System.out.println( "shadow: " +proxy.getClass() + ":" + fact.getClass() ); throw new RuntimeDroolsException( "Error creating shadow fact for object: " + fact, e ); } } return proxy; } []s Edson 2008/2/19, Godmar Back <godmar(a)gmail.com&gt;: As a general comment, the examples for which I find Drools failing are not the actual examples for which my application is failing. It's just the smallest test case I was able to eliminate. I'm now a bit concerned about your comment that Maps and Collections aren't well-defined as Facts. I am planning to make extensive use of them (that's also why I'd prefer to use the MVEL dialect, because in Java I cannot do this without creating Bean wrappers.) Could you elaborate what makes the semantics not "well-defined". I'm specifically concerned with immutable maps (such as the one that would have been returned by Collections.singletonMap), and with collections of maps (such as those obtained via a "from"..." clause). I need to insert immutable maps as facts; I understand that the items returned by "from" aren't inserted as facts. - Godmar On Feb 19, 2008 3:11 PM, Edson Tirelli <tirelli(a)post.com&gt; wrote: 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(a)gmail.com&gt;: 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 _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users -- Edson Tirelli JBoss Drools Core Development Office: +55 11 3529-6000 Mobile: +55 11 9287-5646 JBoss, a division of Red Hat @ www.jboss.com _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users -- Edson Tirelli JBoss Drools Core Development Office: +55 11 3529-6000 Mobile: +55 11 9287-5646 JBoss, a division of Red Hat @ www.jboss.com _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users -- Edson Tirelli JBoss Drools Core Development Office: +55 11 3529-6000 Mobile: +55 11 9287-5646 JBoss, a division of Red Hat @ www.jboss.com _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users -- Edson Tirelli JBoss Drools Core Development Office: +55 11 3529-6000 Mobile: +55 11 9287-5646 JBoss, a division of Red Hat @ www.jboss.com _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users ________________________________ _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users