Java EE | ejb3 | 运行时调度

Question

I would like to call an ejb3 at runtime. The name of the ejb and the method name will only be available at runtime, so I cannot include any remote interfaces at compile time.

String bean = 'some/Bean';
String meth = 'doStuff';

//lookup the bean
Object remoteInterface = (Object) new InitialContext().lookup(bean);

//search the method ..
// foreach (methods)
// if method == meth, method.invoke(bean);

the beans should be distributed accross multiple application servers, and all beans are to be called remotely.

Any hints? specifically i do not want:

1. dependency injection
2. inclusion of appliation specific ejb interfaces in the dispatcher (above)
3. webservices, thats like throwing out processing power for nothing, all the xml crap

Is it possible to load an ejb3 remote interface over the network (if yes, how?), so I could cache the interface in some hashmap or something.

I have a solution with a remote dispatcher bean, which I can include in the above main dispatcher, which does essentially the same, but just relays the call to a local ejb (which I can lookup how? naming lookup fails). Given the remote dispatcher bean, I can use dependency injection.

thanks for any help

(netbeans and glassfish btw)

Answer 1

ejb3 calls use RMI. RMI supports remote class loading, so i'd suggest looking into that.

also, JMX mbeans support fully untyped, remote invocations. so, if you could use mbeans instead of session beans, that could work. (JBoss, for instance, supports ejb3-like mbeans with some custom annotations).

lastly, many app servers support CORBA invocations, and CORBA supports untyped method invocations.

Answer 2

You might be able to use java.rmi.server.RMIClassLoader for the remote class loading. You'll also need to load any classes that the remote service returns or throws.

Answer 3

It cannot be done. You will always get a "class not found" exception. That is in my opinion the biggest disadvantage of EJB/Java. You loose some of the dynamcis, because the meta-language features are limited.

EJB3 supports RMI/IIOP, but not RMI/JRMP (standard RMI) so dynamic class loading is not supported.You loose some Java generality, but gain other features like being able to communicate about transactions and security.

Answer 4

You need to use reflection for this, and it is very simple to do. Assuming that you're looking for a void method called meth :

Object ejb = ctx.lookup(bean);
for (Method m : ejb.getClass().getMethods()) {
    if (m.getName().equals(meth) && m.getParameterTypes().length == 0) {
        m.invoke(service);
    }
}

If you're looking for a specific method signature just modify the m.getParameterTypes() test accordingly, eg for a method with a single String parameter you can try:

Arrays.equals(m.getParameterTypes(), new Class[]{String.class})

And then pass an Object[] array with the actual arguments to the m.invoke() call:

m.invoke(service, new Object[]{"arg0"})