How do I manage dynamic dependencies with PicoContainer?

Question

Say I have two classes A and B, with B depending on A.

public class A {}

public class B {
    public B(A a) {}
}

It's easy to resolve B in a single PicoContainer.

    final MutablePicoContainer root = new PicoBuilder().build();
    root.addComponent(new A());
    root.addComponent(B.class, B.class);
    System.out.println(root.getComponent(B.class));

But I'd like to have different instances of B for different sessions, with variable instances of A. I'm thinking about something like this.

    // during startup
    final MutablePicoContainer root = new PicoBuilder().build();
    root.addComponent(B.class, B.class);

    // later, initialize sessions
    final MutablePicoContainer session = new PicoBuilder(root)
        .implementedBy(TransientPicoContainer.class)
        .build();
    session.addComponent(new A());

    // some request
    System.out.println(session.getComponent(B.class));

Above code isn't working, because when asking session for a B it asks the parent container root for it. B is found there, but resolved only within root and its parents, leading to an UnsatisfiableDependenciesException.

Is there any good way to make this work? Or is this an anti-pattern, and I'm solving the problem in the wrong way?

You should better use Spring! It's business proven. So much people have afford with a picoc=>spring migration because pico container was to unstable and buggy... — Martin K., May 12 '09 at 12:47
I disagree. Pico is a *much* better container than Spring's. The advantage in Spring is its community, not its technology. — erickson, May 12 '09 at 14:51
@Ronald - I don't understand exactly what your goal is. Do you want a new A and a corresponding new B to be created for each session? Why not use your "single container" pattern to register A and B in the session container rather than the root? — erickson, May 12 '09 at 14:54
@erickson: Yes, a new B for each session, and there can be multiple sessions at the same time. A single container would work, and would arguably be even more correct. But the sessions are rather short lived, so I thought it would be better (CPU and memory wise) if there's a "static" parent and multiple "dynamic" transient session containers. Maybe a proto-container from which each session container is copied would be better, instead of a root/sessions hierarchy that acts like one big container. — Ronald Blaschke, May 12 '09 at 15:32

score 1 · Answer 1 · answered May 14 '09 at 12:50

1

Solving a performance problem that doesn't exist isn't a good approach. Have you done any profiling to verify the problem?

If not, consider doing that first.

answered May 14 '09 at 12:50

Jörn Zaefferer

5,665
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score 1 · Answer 2 · answered Jun 05 '09 at 11:15

1

Did you enable caching on your container (or are you using Pico 1.x)?

Try reading this, maybe disabling the cache is enough to solve this problem.

answered Jun 05 '09 at 11:15

score 0 · Accepted Answer · answered Jun 04 '09 at 08:35

I would register B within the session container as well. Any other dependency of B you can leave in the root container. Assume B has another dependency on C. So you can do the following:

// during startup
final MutablePicoContainer root = new PicoBuilder().build();
root.addComponent(C.class, C.class);

// later, initialize sessions
final MutablePicoContainer session = new PicoBuilder(root)
    .implementedBy(TransientPicoContainer.class)
    .build();
session.addComponent(B.class, B.class);
session.addComponent(new A());

// some request
System.out.println(session.getComponent(B.class));

How do I manage dynamic dependencies with PicoContainer?

3 Answers3