实现一个简单的 AOP 功能

通过动态代理，将横切代码块与业务代码分离。

JDK 动态代理方式

public class TransactionProxyFactory<T> implements InvocationHandler {

    private final T t;

    public TransactionProxyFactory(T t) {
        this.t = t;
    }

    public <E extends T> T getTarget() {
        return (E) Proxy.newProxyInstance(t.getClass().getClassLoader(), t.getClass().getInterfaces(), this);
    }
    
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        try {
            TransactionManager.beginTransaction();

            Object result = method.invoke(t, args);

            TransactionManager.commit();
            return result;
        } catch (Exception e) {
            e.printStackTrace();
            TransactionManager.rollback();
            throw e;
        }
    }
}

Cglib 动态代理方式

public class TransactionCglibProxyFactory<T> implements MethodInterceptor {

    private final Class<? extends T> clazz;

    public TransactionCglibProxyFactory(Class<? extends T> clazz) {
        this.clazz = clazz;
    }

    public <E extends T> T getTarget() {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(clazz);
        enhancer.setCallback(this);
        return (E) enhancer.create();
    }

    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        try {
            TransactionManager.beginTransaction();

            Object result = proxy.invokeSuper(obj, args);

            TransactionManager.commit();
            return result;
        } catch (Exception e) {
            e.printStackTrace();
            TransactionManager.rollback();
            throw e;
        }
    }
}

使用时调用代理对象

结合了之前写的 IoC 容器。

private final TransferService transferService = new TransactionProxyFactory<>(
        (TransferService) BeanFactory.getBean("transferService")).getTarget();