public interface UserService {
    String doSomething();
}
@Service
public class UserServiceImpl implements UserService {
    @Override
    public String doSomething() {
        System.out.println("doSomething......");
    }
}
@Controller
public class UserController {
    @Autowired
    private UserService userService;
    public void test(){
        String response = userService.doSomething();
    }
}

public interface UserService { //假設(shè)這是服務(wù)端暴露出來(lái)的接口
    String doSomething();
}
@Controller
public class UserController {
    @Autowired
    private UserService userService;//對(duì)于客戶端來(lái)說(shuō)，此時(shí)沒(méi)有實(shí)現(xiàn)類(lèi)，無(wú)法直接使用
    public void test(){
        String response = userService.doSomething();
    }
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Import({ServiceBeanDefinitionRegistry.class}) //注意看這個(gè)地方比較重要
public @interface RPC {
    String value() default ""; //掃描的路徑
}
//簡(jiǎn)單用法
@SpringBootApplication
@RPC("com.yeyeye.client.service") //掃描對(duì)應(yīng)包下的所有接口，service包下就一個(gè)上面示例中的 UserService 接口
public class RpcClientApplication {
    public static void main(String[] args) {
        SpringApplication.run(RpcClientApplication.class, args);
    }
}

public class ServiceBeanDefinitionRegistry implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        //獲取RPC注解里的路徑
        Map<String, Object> attributes = importingClassMetadata.getAnnotationAttributes(RPC.class.getName());
        if (MapUtil.isEmpty(attributes)) {
            return;
        }
        String basePackages = (String) attributes.get("value");
        if (basePackages == null) {
            return;
        }
        //掃描路徑
        RpcScanner rpcScanner = new RpcScanner(registry);
        rpcScanner.addIncludeFilter((metadataReader, metadataReaderFactory) -> true);
        rpcScanner.scan(basePackages);
    }
}

public class RpcScanner extends ClassPathBeanDefinitionScanner {
    public RpcScanner(BeanDefinitionRegistry registry) {
        super(registry);
    }
    @Override
    protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
        //是不是一個(gè)接口，是的話就添加為候選組件
        return beanDefinition.getMetadata().isInterface();
    }
    @Override
    protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
        //這里就是具體利用spring幫我們掃描
        Set<BeanDefinitionHolder> beanDefinitionHolders = super.doScan(basePackages);
        //對(duì)掃描出來(lái)的結(jié)果進(jìn)行處理
        for (BeanDefinitionHolder beanDefinitionHolder : beanDefinitionHolders) {
            //這里獲取的beanDefinition都是接口，并沒(méi)有實(shí)現(xiàn)類(lèi)
            BeanDefinition beanDefinition = beanDefinitionHolder.getBeanDefinition();
            //注冊(cè)一個(gè)我們自己的beanDefinition，這個(gè)beanDefinition是一個(gè)bean工廠，工廠用于生成接口的代理類(lèi)
            beanDefinition.setBeanClassName(ServiceBeanFactory.class.getName());
            //這里就是工廠bean構(gòu)造方法需要的參數(shù)
            beanDefinition.getConstructorArgumentValues()
            .addGenericArgumentValue(beanDefinition.getBeanClassName());
        }
        return beanDefinitionHolders;
    }
}

public class ServiceBeanFactory<T> implements FactoryBean<T> {
    private Class<T> interFaceClazz;
    public ServiceBeanFactory(Class<T> interFaceClazz) {
        this.interFaceClazz = interFaceClazz;
    }
    @Override
    public T getObject() throws Exception {
        return (T) Proxy.newProxyInstance(
                interFaceClazz.getClassLoader(),
                new Class[]{interFaceClazz},
                new ServiceInvocationHandler());
    }
    @Override
    public Class<?> getObjectType() {
        return interFaceClazz;
    }
}
public class ServiceInvocationHandler implements InvocationHandler {
    /**
     * 這里就直接進(jìn)行遠(yuǎn)程RPC調(diào)用了
     */
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) {
        //指定URL
        String url = "http://localhost:8888/" + method.getName();
        //發(fā)送get請(qǐng)求并接收響應(yīng)數(shù)據(jù)
        return HttpUtil.createGet(url).execute().body();
    }
}