public interface BeanPostProcessor {
    //bean初始化方法調(diào)用前被調(diào)用
    Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
    //bean初始化方法調(diào)用后被調(diào)用
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

}

public class HelloService{
     void sayHello();
     void sayHi();
}

@Service
public class HelloServiceImplV1 implements HelloService{
     public void sayHello(){
          System.out.println("Hello from V1");
     }
     public void sayHi(){
          System.out.println("Hi from V1");
     }
}

@Service
public class HelloServiceImplV2 implements HelloService{
     public void sayHello(){
          System.out.println("Hello from V2");
     }
     public void sayHi(){
          System.out.println("Hi from V2");
     }
}

@Controller
public class HelloController{
     @Autowird
     private HelloServiceImplV1 helloServiceImplV1；
     @Autowird
     private HelloServiceImplV2 helloServiceImplV2；

     public void sayHello(){
          if(getHelloVersion()=="A"){
               helloServiceImplV1.sayHello();
          }else{
               helloServiceImplV2.sayHello();
          }
     }
     public void sayHi(){
          if(getHiVersion()=="A"){
               helloServiceImplV1.sayHi();
          }else{
               helloServiceImplV2.sayHi();
          }
     }
}

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface RoutingInjected{
}

@Target({ElementType.FIELD,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface RoutingSwitch{
    /**
     * 在配置系統(tǒng)中開關(guān)的屬性名稱，應(yīng)用系統(tǒng)將會實(shí)時(shí)讀取配置系統(tǒng)中對應(yīng)開關(guān)的值來決定是調(diào)用哪個(gè)版本
     * @return
     */
     String value() default "";
}

@RoutingSwitch("hello.switch")
public class HelloService{

    @RoutingSwitch("A")
    void sayHello();

    void sayHi();
}

@Controller
public class HelloController{
   
    @RoutingInjected
    private HelloService helloService；
    
    public void sayHello(){
        this.helloService.sayHello();
    }

    public void sayHi(){
        this.helloService.sayHi();
    }
}

@Component
public class RoutingBeanPostProcessor implements BeanPostProcessor {

    @Autowired
    private ApplicationContext applicationContext;

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        Class clazz = bean.getClass();
        Field[] fields = clazz.getDeclaredFields();
        for (Field f : fields) {
            if (f.isAnnotationPresent(RoutingInjected.class)) {
                if (!f.getType().isInterface()) {
                    throw new BeanCreationException("RoutingInjected field must be declared as an interface:" + f.getName()
                                    + " @Class " + clazz.getName());
                }
                try {
                    this.handleRoutingInjected(f, bean, f.getType());
                } catch (IllegalAccessException e) {
                    throw new BeanCreationException("Exception thrown when handleAutowiredRouting", e);
                }
            }
        }
        return bean;
    }

    private void handleRoutingInjected(Field field, Object bean, Class type) throws IllegalAccessException {
        Map<String, Object> candidates = this.applicationContext.getBeansOfType(type);
        field.setAccessible(true);
        if (candidates.size() == 1) {
            field.set(bean, candidates.values().iterator().next());
        } else if (candidates.size() == 2) {
            Object proxy = RoutingBeanProxyFactory.createProxy(type, candidates);
            field.set(bean, proxy);
        } else {
            throw new IllegalArgumentException("Find more than 2 beans for type: " + type);
        }
    }
}

public class RoutingBeanProxyFactory {

    public static Object createProxy(Class targetClass, Map<String, Object> beans) {
        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.setInterfaces(targetClass);
        proxyFactory.addAdvice(new VersionRoutingMethodInterceptor(targetClass, beans));
        return proxyFactory.getProxy();
    }
    static class VersionRoutingMethodInterceptor implements MethodInterceptor {
        private String classSwitch;
        private Object beanOfSwitchOn;
        private Object beanOfSwitchOff;

        public VersionRoutingMethodInterceptor(Class targetClass, Map<String, Object> beans) {
            String interfaceName = StringUtils.uncapitalize(targetClass.getSimpleName());
            if(targetClass.isAnnotationPresent(RoutingSwitch.class)){
                this.classSwitch =((RoutingSwitch)targetClass.getAnnotation(RoutingSwitch.class)).value();
            }
            this.beanOfSwitchOn = beans.get(this.buildBeanName(interfaceName, true));
            this.beanOfSwitchOff = beans.get(this.buildBeanName(interfaceName, false));
        }
        
        private String buildBeanName(String interfaceName, boolean isSwitchOn) {
            return interfaceName + "Impl" + (isSwitchOn ? "V2" : "V1");
        }

        @Override
        public Object invoke(MethodInvocation invocation) throws Throwable {
            Method method = invocation.getMethod();
            String switchName = this.classSwitch;
            if (method.isAnnotationPresent(RoutingSwitch.class)) {
                switchName = method.getAnnotation(RoutingSwitch.class).value();
            }
            if (StringUtils.isBlank(switchName)) {
                throw new IllegalStateException("RoutingSwitch's value is blank, method:" + method.getName());
            }
            return invocation.getMethod().invoke(getTargetBean(switchName), invocation.getArguments());
        }

        public Object getTargetBean(String switchName) {
            boolean switchOn;
            if (RoutingVersion.A.equals(switchName)) {
                switchOn = false;
            } else if (RoutingVersion.B.equals(switchName)) {
                switchOn = true;
            } else {
                switchOn = FunctionSwitch.isSwitchOpened(switchName);
            }
            return switchOn ? beanOfSwitchOn : beanOfSwitchOff;
        }
    }
}