Execute code before and after method?

Question

In the service layer I have a classes that look something like:

class MyService {
    public doSomething() {
        TelnetSession session = new TelnetSession();
        session.open("username", "password");
        session.execute("blah");
        session.close();
    }
}

In many classes I have to declare and open session and then at the end close it. I'd rather do something with annotations but I've got no idea where to start. How do other people do something like this:

class MyService {
    @TelnetTransaction
    public doSomething() {
        session.execute("blah");
    }
}

where a method annotated with @TelnetTransaction instantiates, opens and passes in the TelnetSession object.

Thanks,

James

Answer 1

Before and after is what aspect oriented programming is for.

Spring handles transactions with aspects. Give Spring AOP or AspectJ a look.

Answer 2

Unless you are doing something ropey, you want to end up with an object that delegates to a service object, with the execute around. There is no reason for both types to implement exactly the same interface, and good reasons why they should not. There are a number of ways of ending up with this:

• Just do it by hand. I suggest always starting off like this before hitting code generation.
• Use a dynamic proxy. Unfortunately java.lang.reflect.Proxy requires you to add an interface.
• Use APT (or at least the annotation processing facilities in 1.6 javac) to generate the code. Java source is easier than bytecode, but I don't know of any good libraries for Java source code generation.
• Use the Execute Around idiom by hand - verbose and clumsy.

Answer 3

As duffymo says, AOP is the way to go. I'd suggest you to get a copy of

AspectJ in Action

It is written by Ramnivas Laddad, a Spring Committer, and it covers both Spring AOP and "real" AspectJ thoroughly and understandably.

For developing you should use the AspectJ Developer Tools for Eclipse or better yet, the SpringSource Tool Suite (it contains AJDT).

Answer 4

Spring AOP will be your best bet if you are already using that. If you need runtime injection, you would need to use AspectJ. I remember reading Spring does not support that kind of injection