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I've been using the JSON-RPC
library for some time now to write the server for my game, thus far I've only had a need to transport simple objects back to the client, but recently I've had a need send a collection of objects back. This is where I found that JSON-RPC falls short if you try to use the standard Java collections.
I've tried several things, first I used a Collection, which resulted in the following exception:
Caused by: java.lang.IllegalArgumentException: abstract class or interface not allowed : interface java.util.Collection
Then I thought if I used a concrete class, it would fix that, but alas, the following exception is thrown:
Caused by: java.lang.IllegalArgumentException: parametrized classes not allowed : class java.util.ArrayList
So what's a parametrized class? Well that's to do with Java Generics, the ArrayList I had was actually something like an ArrayList and the JSON-RPC library doesn't know how to handle that.
It looks like all of the Java collections now are parametrized, so using them will not work. The only thing I found that would work was to send an array of my objects instead. This is a bit messy since it means I have to allocate my array on the server side with a known size, with a collection I was just using lazy loading, which saved me some hassle.
So to sum up, my object that was being returned to the client had to change from this:
private List<MyOtherClass> otherClass;
private MyOtherClass otherClass;
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