Code generation through Java Reflection

Question

Hi
I am after some clarification about the possibility of mapping of method outputs to other method inputs, using java reflection.
The java objects are described in an XML based language (called DAML) as follows
<java:Method rdf:ID="meth1" java:priority="1">
<java:methodName>buildQuery</java:methodName>
<java:parentClass>afsw.query.QueryBuilder</java:parentClass>
<java:methodParameters rdf:parseType="daml:collection">
<java:Parameter>
<java:inORout>input</java:inORout>
<java:type>java.util.Hashtable</java:type>
</java:Parameter>
</java:methodParameters>
</java:Method>
and I want to map them back to method calls and instantiations, so to be able to generate code on the fly. I need to know if its is possible to pass the output of a method such as getQuery() which in this case is a Document to the input of constructor MsgModule as in the following example:
Document queryDoc =qc.getQuery();
MsgModule mg= new MsgModule(queryDoc);
regards
Charlie

Answer 1

This is possible. What you need to do in the 'new' instance case is to find the best constructor. So let's say you have Class clazz, the class you want to create a new instance of, and Class[] params, an array of objects to pass in the constructor. Using the Class api you can do:
Constructor constructor = clazz.getConstructor(params);The getConstructor method will only return an exact match. Let's say one of the parameters was a subclass of an class that is allowable in the constructor. You can get all the constructors via clazz.getConstructors() and get all the parameters types via Constructor.getParameterTypes() and check to see if the params you passed in are compatible. You can use Class.isAssignableFrom() to help resolve this. Once you find the constructor, use Constructor.newInstance(params) to create the new instance. Hope this helps.