背景
一直以来，使用 Spring Cloud OpenFeign 都是阅读官方文档，虽然也大概知道其实现原理，但终究是没有"证据"的。关于 Spring 的源码阅读，自认为是一件十分令人头疼的事情。最近，在学习 Feign 的原生 API，乘此机会，也就阅读一下 Spring Cloud OpenFeign 的源码，并将分享出来，希望能帮到有需要的人吧。
概述
关于 Spring Cloud OpenFeign 源码的博客有很多，但是，不知道为什么，照着博客，一边读博客，一边读源码，还一边 debug，总是认为还有很多不清楚的地方。究其原因，我认为，博客都是按照源码的流程讲解，虽然附上了大段代码，可能还是无法清晰的理解。不知道你们是不是，反正我是这样的。
目标
首先，我们明确一下今天探究的问题：
- 我们知道，当我们使用
@FeignClient，是使用了JDK动态代理，那么是如何实现的，那一步创建的代理类。 - 当我们知道第一个问题后，我们就基本清楚整个流程了，那么，我们就可以手写一个简易的入门测试了。
源码
启动流程
- org.springframework.cloud.openfeign.EnableFeignClients
- org.springframework.cloud.openfeign.FeignAutoConfiguration
- org.springframework.cloud.openfeign.FeignClientsRegistrar
- org.springframework.cloud.openfeign.FeignClientsRegistrar#registerBeanDefinitions
- org.springframework.cloud.openfeign.FeignClientsRegistrar#registerFeignClient
- org.springframework.cloud.openfeign.FeignClientFactoryBean#getObject
- org.springframework.cloud.openfeign.Targeter
- feign.Feign.Builder#build
- feign.SynchronousMethodHandler.Factory
- feign.ReflectiveFeign.ParseHandlersByName
- feign.ReflectiveFeign#ReflectiveFeign
- feign.Feign#newInstance
- feign.ReflectiveFeign#newInstance
- feign.InvocationHandlerFactory#create
- feign.InvocationHandlerFactory.Default#create
- feign.ReflectiveFeign.FeignInvocationHandler#FeignInvocationHandler
贴上图吧，看看完整版的
注册流程：
自动配置：
调用流程
- feign.ReflectiveFeign.FeignInvocationHandler#invoke
- feign.InvocationHandlerFactory.MethodHandler#invoke
- feign.SynchronousMethodHandler#invoke
MyRpc
经过上面的流程，我们手写一个 RPC。
下面给出主要代码。
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import({MyRpcRegister.class, MyRpcAutoConfig.class})
public @interface EnableMyRpc {
}getObject()
@Data
public class MyRpcFactoryBean implements FactoryBean<Object> {
private String url;
private String contextPath;
private String name;
private Class<?> type;
private BeanFactory beanFactory;
private MyClient myClient;
@Override
public Object getObject() {
Map<Method, RpcBean> map = new HashMap<>();
Method[] methods = type.getMethods();
myClient = beanFactory.getBean(MyClient.class);
for (Method method : methods) {
Annotation[] annotations = method.getAnnotations();
String httpMethod = "";
String path = "";
for (Annotation annotation : annotations) {
if (annotation.annotationType() == PostMapping.class) {
httpMethod = "POST";
path = ((PostMapping) annotation).value()[0];
break;
} else if (annotation.annotationType() == GetMapping.class) {
httpMethod = "GET";
path = ((GetMapping) annotation).value()[0];
break;
} else if (annotation.annotationType() == RequestMapping.class) {
RequestMapping requestMapping = ((RequestMapping) annotation);
httpMethod = requestMapping.method()[0].name();
path = requestMapping.value()[0];
break;
}
}
RpcBean rpcBean = new RpcBean()
.setUrl(url + contextPath)
.setPath(path)
.setHttpMethod(httpMethod)
.setMyClient(myClient)
;
map.put(method, rpcBean);
}
ClassLoader loader = type.getClassLoader();
return Proxy.newProxyInstance(loader, new Class<?>[] {type}, new MyRpcInvocationHandler(map));
}
@Override
public Class<?> getObjectType() {
return type;
}
}handler
@Slf4j
public class MyRpcInvocationHandler implements InvocationHandler {
private final Map<Method, RpcBean> map;
public MyRpcInvocationHandler(Map<Method, RpcBean> map) {
this.map = map;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
log.info("proxy handler");
return request(method, args);
}
public Object request(Method method, Object[] args) {
String result = "";
RpcBean rpcBean = map.get(method);
Parameter[] parameters = method.getParameters();
Class<?> returnType = method.getReturnType();
String url = rpcBean.getUrl() + rpcBean.getPath();
String httpMethod = rpcBean.getHttpMethod();
String param = getParam(httpMethod, parameters, args);
log.info("url: [{}], param: [{}]", url, param);
MyClient myClient = rpcBean.getMyClient();
if ("POST".equals(httpMethod)) {
result = myClient.post(url, param);
} else if ("GET".equals(httpMethod)) {
result = myClient.get(url, param);
}
if (StringUtils.hasText(result)) {
return JsonUtils.convertObject(result, returnType);
}
return "";
}
public String getParam(String httpMethod, Parameter[] parameters, Object[] args) {
if ("POST".equals(httpMethod)) {
return JsonUtils.convertString(args[0]);
} else if ("GET".equals(httpMethod)) {
if (Objects.isNull(parameters) || parameters.length == 0
|| Objects.isNull(args) || args.length == 0) {
return "";
}
String param = "";
StringBuilder urlBuilder = new StringBuilder(param);
for (int i = 0; i < parameters.length; i++) {
if (Objects.nonNull(args[i])) {
urlBuilder.append(String.format("%s=%s&", parameters[i].getName(), args[i]));
}
}
param = urlBuilder.toString();
param = param.substring(0, param.length() - 1);
return param;
}
return "";
}
}