Concurrency, reflection and Factory pattern

Hi everyone,

Here is my problem:

Case:
- server application which launches concurrently tasks (precisely
classes extending class Task)
- new types of task can be registered at the server by the developer
- only class of task which matches incoming request, is launched

Proposed solution:
- Developer registers not instances of tasks, but their classes in the
server
- If static method matches() of one task's class returns true, then
this class is instancianized by use of Java reflection

Pros:
1. no instance of Task class is necessary to check its matching
condition
2. both: matching condition and related solve() method are defined in a
single class

Cons:
1. this approach is easy to abuse, since static methods cannot be
abstract and or overriden, which does not force developer to implement
them in classes which derive from Task class.

I was wondering about using Factory pattern, which creates instances of
class, but this forces me to break 2nd advantage. Do you see any other
solution ?

TIA,
Maciej

ps. Here is example of Task class

public abstract class Task<R,T> {

        private R request;

        /* This method must be implemented in deriving class */
        public abstract T solve();

        /* This method method must be over-hidden in deriving class. */
        public static boolean matches(R request) {
                return false;
        }

        public Task(R request) {
                this.request = request;
        }