是否可以在运行时将自己动态创建的对象注册为spring bean？

Question

I need to use Spring AOP facility and would not like to make AspectJ integration in order to intercept a method call to an object which is not initially a spring bean. The object is going to be created dynamically in runtime . It's not possible for me to add a bean definition into ApplicationContext configuration file. So does spring provide such a facility?

Answer 1

Yes, it's possible. You could create a prototype scoped bean with @Bean and @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE) in a @Configuration bean, which would act as a factory:

@Configuration
public class Factory {

    public static class A {

        private final int x;

        public A(int x) {
            this.x = x;
        }
    }

    @Bean
    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    @Autowired
    public A getA(int arg) {
        try {
            return A.class.getConstructor(int.class).newInstance(arg);
        } catch (Exception e) {
            throw new BeanCreationException("A" + arg, "Could not create instance of bean A", e);
        }
    }

    @Bean
    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    public int getArg() {
        return (int) (Math.random() * 2 + 1);
    }

    @PostConstruct
    public void test() {

        int r1 = this.getArg();
        A a1 = this.getA(r1);
        System.out.println("a1.x = " + a1.x); // 1 or 2

        int r2 = this.getArg();
        A a2 = this.getA(r2);
        System.out.println("a2.x = " + a2.x); // 2 or 1, different to a1.x
    }
}

In method getA() , I could have created an instance of the A bean just with new A(arg) , however I created it dynamically, so that it's closer to your use case.

Note that from Spring 4.x version onwards, you can use @Autowired to autowire the parameters of the bean to be returned by a @Bean method, meaning that those parameters can be other beans, even of primitive types. That's why I made the argument of the A bean to also be a prototype scoped bean.

Then in the @PostConstruct method (which I'm using as a test), I get two instances of the int argument and two instances of the A bean, and assign each one of them to each instance of A .

If I hadn't used the @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE) annotation, both getArg() and getA(arg) @Bean methods would have returned the same instance when invoked for the second time, as Spring's default scope for beans is ConfigurableBeanFactory.SCOPE_SINGLETON . If this is the behavior you expect, just remove the @Scope annotations.