April 23, 2004

I have spent quite a bit of time lately exploring various aop, ioc, and mvc frameworks and the one thing that seems to plague them all is the insidious desire to wire everything together with xml. i will not make an argument against xml for configuration, because it is a trite endeavour, and instead attempt to outline the benefits of using a scripting language such as bsh.

fortunately dynaop and picocontainer both provide bsh integration so i will attempt to outline my findings, which will be the foundation for my next article addressing mvc frameworks.

I have found dependency injection and picocontainer in particular quite ingenious, but found hardcoding the wiring of pico components rather undesirable. nanocontainer to the rescue. nanocontainer provides a thin wrapper around bsh which provides the ability to wire components through a bsh script.

before i delve into the specifics of bsh configuration i will outline the obligatory Foo and Bar components that will be used to test the bsh configuration.

public interface Foo {
    public Bar foo();
}

public class FooImpl implements Foo {
    private String foo;
    private Bar bar;

    public FooImpl(Bar bar, String foo) {
        this.foo = foo;
        this.bar = bar;
    }

    public Bar foo() {
        System.out.println(this.foo);
        return this.bar;
    }
}

public interface Bar {
    public void bar();
}

public class BarImpl implements Bar {
    private Foo foo;

    public BarImpl(Foo foo) {
        this.foo = foo;
    }

    public void bar() {
        foo.foo();
        System.out.println("bar");
    }
}

import java.io.InputStreamReader;
import java.io.Reader;

import org.nanocontainer.script.bsh.BeanShellContainerBuilder;

import org.picocontainer.PicoContainer;
import org.picocontainer.defaults.DefaultPicoContainer;
import org.picocontainer.defaults.ObjectReference;
import org.picocontainer.defaults.SimpleReference;

public class BshNanocontainerTest {
    public static void main(String[] args) throws Exception {
        new BshNanocontainerTest().testBsh();
    }

    void testBsh() throws Exception {
        Reader reader = new InputStreamReader(
            Thread.currentThread().getContextClassLoader().getResource(
                "nanocontainer.bsh").openStream());

        BeanShellContainerBuilder builder = new BeanShellContainerBuilder(
            reader, Thread.currentThread().getContextClassLoader());

        ObjectReference container = new SimpleReference();
        container.set(new DefaultPicoContainer());

        builder.buildContainer(container, new SimpleReference(),
            this.toString());

        PicoContainer pico = (PicoContainer) container.get();
        //System.out.println(pico.getComponentInstance("bar"));

        //System.out.println(pico.getComponentInstance("foo"));
        Foo foo = (Foo) pico.getComponentInstance("foo");
        foo.foo().bar();

        foo = (Foo) pico.getComponentInstance(Foo.class);
        foo.foo().bar();
        //System.out.println(foo.foo().bar());
    }
}

• get an instance of Bar named "bar" from pico.
• get an instance of Foo named "foo" from pico.
• get an instance of Foo named Foo.class from pico.

import org.picocontainer.*;
import org.picocontainer.defaults.*;
import org.nanocontainer.script.bsh.BeanShellComponentAdapterFactory;

pico = new DefaultPicoContainer(
    new ImplementationHidingComponentAdapterFactory(), parent);

//pico.registerComponentInstance("bar", new BarImpl());
pico.registerComponentImplementation("bar", BarImpl.class);
//pico.registerComponentImplementation(BarImpl.class);

pico.registerComponentImplementation(
    Foo.class, FooImpl.class, new Parameter[] {
        new ComponentParameter("bar"), new ConstantParameter("testing") });

pico.registerComponent(
    new BeanShellComponentAdapterFactory().createComponentAdapter(
        "foo", FooImpl.class, null));

import dynaop.*;

instance = ProxyFactory.getInstance().wrap(
    picoContainer.getComponentInstance(Foo.class));
    //new FooImpl(picoContainer.getComponentInstance("bar"), "test"));

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