At work one of our developers is programming an ecommerce store against a Java API written by a third party. Said Java API returns a TreeMap object from a method and when you try to access that TreeMap object in any fashion, you’ll get an error, specifically:

“Error casting an object of type java.lang.Integer to an incompatible type. This usually indicates a programming error in Java, although it could also mean you have tried to use a foreign object in a different way than it was designed.”

What we’ve concluded is that ColdFusion attempts to cast any and all Java classes that implement the Map interface to:

coldfusion.runtime.Struct

which is of type java.util.Hashtable. Unfortunately, a TreeMap uses an Object (in this case an Integer) as the key. ColdFusion structures can only use strings as the key. The takeaway is that this is a ‘feature’ of ColdFusion, it’s nice that it attempts to transform collection type objects into the native ColdFusion structure type. In this specific case, it’s more of a hindrance. The workaround is to create your own Java wrapper that takes the TreeMap, loops over all the keys, inserting each into a Vector and then return the Vector to ColdFusion, which turns that into a structure.

In case you don’t feel comfortable going to sleep at night without seeing the code, here’s an example Java class that returns a simple TreeMap:

import java.util.*;
public class TreeMapTest {
   public static TreeMap getTree() {
      TreeMap t = new TreeMap();
      t.put(new Integer(131000), “product”);
      return t;
   }
}

Compile that and then drop it into your [cfusionmx]\wwwroot\WEB-INF\lib\ directory. You can use this script to test it:

<cfscript>
   tmt = createObject(“java”, “TreeMapTest”);
   WriteOutput(“tmt is of type ” & tmt.getClass());
   treeMap = tmt.getTree();
   WriteOutput(“treeMap is of type ” & treeMap.toString()); // you get an error here
</cfscript>

I’d be very very interested in hearing about any ways that you know of to get around something like this without having to write a wrapper class. And for you Macromedia ColdFusion guys, it might be a nice (albeit probably rarely used) feature to be able to maintain the Java type of an object by using some function, ( ie: maintainType() or some such).

By the way, if you’re interested in knowing more about using Java and ColdFusion together, Terry Ford has written a great article here entitled “Using Java and J2EE Elements in ColdFusion MX Applications”.