Question

A common pattern I am falling into with my beans is as follows:

public class PrototypeBean {
    private SingletonBean singletonBean;
    private int value;
    public PrototypeBean(int value, singletonBean) {
        this.value = value;
        this.singletonBean = singletonBean;
    }
}

I cannot for the life of me figure out what is the cleanest way to instantiate a prototype bean like this if I do not know what value will be until runtime. My current pattern is as follows:

public class FactoryImpl implements Factory{
    private SingletonBean singletonBean;

    public FactoryImpl(SingletonBean singletonBean) {
       this.singletonBean = singletonBean;
    }

    public PrototypeBean getPrototypeBean(int value) {
       return new PrototypeBean(value, singletonBean);
    }
}

Where Factoryimpl is wired together in XML. This still seems horrible to me and feels like I am breaking IoC. Is there a cleaner way of doing this in spring?

Answer 1

This is one of the most wanted features missing in Spring I came across. Basically your solution is the best workaround I can think of (just make singletonBean and value fields final).

Another approach would be to let Spring create PrototypeBean with only one constructor argument (SingletonBean) and passing value afterwards (see: Best way to refactor this in Spring?). However this is less clean as it allows one to create half-initialized object.

The best solution would be to take advantage of parametrized <lookup-method/> – feature that waits to be implemented in Spring: SPR-7431. Don’t forget to vote and comment!