【feign源码】流程分析

Feign的接口和Mybatis的接口相似，都是通过FactoryBean实现了spring整合的，那么扫包的就不再分析了，直接看FactoryBean–FeignClientFactoryBean

 @Overridepublic Object getObject() throws Exception {return getTarget();}

 <T> T getTarget() {FeignContext context = this.applicationContext.getBean(FeignContext.class);// 配置FeginFeign.Builder builder = feign(context);if (!StringUtils.hasText(this.url)) {if (!this.name.startsWith("http")) {this.url = "http://" + this.name;}else {this.url = this.name;}this.url += cleanPath();return (T) loadBalance(builder, context,new HardCodedTarget<>(this.type, this.name, this.url));}if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {this.url = "http://" + this.url;}String url = this.url + cleanPath();Client client = getOptional(context, Client.class);if (client != null) {if (client instanceof LoadBalancerFeignClient) {// not load balancing because we have a url,// but ribbon is on the classpath, so unwrapclient = ((LoadBalancerFeignClient) client).getDelegate();}if (client instanceof FeignBlockingLoadBalancerClient) {// not load balancing because we have a url,// but Spring Cloud LoadBalancer is on the classpath, so unwrapclient = ((FeignBlockingLoadBalancerClient) client).getDelegate();}builder.client(client);}// 返回实例；Targeter targeter = get(context, Targeter.class);return (T) targeter.target(this, builder, context,new HardCodedTarget<>(this.type, this.name, url));}

本方法才是精髓，用于配置Feign；这里有一个特殊的地方，就是每个Feign客户端是多例的，这样就可以实现定制客户端。那么怎么区分配置呢？这就用到了FeignContext ，每个客户端，有各自的配置容器。这方面的就不展开了。自己分析吧。

 protected Feign.Builder feign(FeignContext context) {FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);Logger logger = loggerFactory.create(this.type);// 从容器中找到类型，配置FeignFeign.Builder builder = get(context, Feign.Builder.class)// required values.logger(logger).encoder(get(context, Encoder.class)).decoder(get(context, Decoder.class)).contract(get(context, Contract.class));// @formatter://配置FeignconfigureFeign(context, builder);return builder;}

开发者可以通过配置文件，定制每个客户端的每个组件。格式是：
feign.client.客户端的名称，即访问服务的名称.FeignClientConfiguration中的属性。例如：
feign.client.springcloud-demo-provier.contract=com.test.MyContract

 protected void configureFeign(FeignContext context, Feign.Builder builder) {FeignClientProperties properties = this.applicationContext.getBean(FeignClientProperties.class);if (properties != null) {if (properties.isDefaultToProperties()) {configureUsingConfiguration(context, builder);configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()),builder);configureUsingProperties(properties.getConfig().get(this.contextId),builder);}else {configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()),builder);configureUsingProperties(properties.getConfig().get(this.contextId),builder);configureUsingConfiguration(context, builder);}}else {configureUsingConfiguration(context, builder);}}

定制服务有两种方法，一种是配置文件，第二种是通过注解FeignClient中的configuration属性，配置自己的。例如：FeignClientsConfiguration，把自己的组件，以配置的形式编写。

创建实例

在getObejct()方法的最后是创建实例的逻辑。其实调用的是builder中的target方法。

Targeter targeter = get(context, Targeter.class);return (T) targeter.target(this, builder, context,new HardCodedTarget<>(this.type, this.name, url));

feign.Feign.Builder#target(feign.Target)

    public <T> T target(Target<T> target) {return build().newInstance(target);}public Feign build() {//方法处理器SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,logLevel, decode404, closeAfterDecode, propagationPolicy);// 这个类就是用来解析接口类的，之后转化为方法处理器        ParseHandlersByName handlersByName =new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder,errorDecoder, synchronousMethodHandlerFactory);return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder);}

  public <T> T newInstance(Target<T> target) {// 这块已经给分析了一大半了，其实就是将接口类解析出来，之后创建方法处理对象。Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();// 得到方法和方法处理器的映射。for (Method method : target.type().getMethods()) {if (method.getDeclaringClass() == Object.class) {continue;} else if (Util.isDefault(method)) {DefaultMethodHandler handler = new DefaultMethodHandler(method);defaultMethodHandlers.add(handler);methodToHandler.put(method, handler);} else {methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));}}InvocationHandler handler = factory.create(target, methodToHandler);// 动态代理创建对象。T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),new Class<?>[] {target.type()}, handler);for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {defaultMethodHandler.bindTo(proxy);}return proxy;}

InvocationHandler 很简单，有个方法和方法处理器的映射，家用那个方法，直接找对应的方法处理器。

  public Object invoke(Object[] argv) throws Throwable {// 这里是使用真正的值替换占位符；得到RequestTemplate RequestTemplate template = buildTemplateFromArgs.create(argv);Options options = findOptions(argv);Retryer retryer = this.retryer.clone();while (true) {try {// client的发送逻辑了    return executeAndDecode(template, options);} catch (RetryableException e) {try {retryer.continueOrPropagate(e);} catch (RetryableException th) {Throwable cause = th.getCause();if (propagationPolicy == UNWRAP && cause != null) {throw cause;} else {throw th;}}if (logLevel != Logger.Level.NONE) {logger.logRetry(metadata.configKey(), logLevel);}continue;}}}

替换占位符

public RequestTemplate create(Object[] argv) {//克隆对象 RequestTemplate mutable = RequestTemplate.from(metadata.template());if (metadata.urlIndex() != null) {int urlIndex = metadata.urlIndex();checkArgument(argv[urlIndex] != null, "URI parameter %s was null", urlIndex);mutable.target(String.valueOf(argv[urlIndex]));}Map<String, Object> varBuilder = new LinkedHashMap<String, Object>();// 得到占位符和真正值的对应关系for (Entry<Integer, Collection<String>> entry : metadata.indexToName().entrySet()) {int i = entry.getKey();Object value = argv[entry.getKey()];if (value != null) { // Null values are skipped.if (indexToExpander.containsKey(i)) {value = expandElements(indexToExpander.get(i), value);}for (String name : entry.getValue()) {varBuilder.put(name, value);}}}// 替换占位符，这里有不同了，子类的实现同，涉及到解析请求体，请求参数的不同RequestTemplate template = resolve(argv, mutable, varBuilder);if (metadata.queryMapIndex() != null) {// add query map parameters after initial resolve so that they take// precedence over any predefined valuesObject value = argv[metadata.queryMapIndex()];Map<String, Object> queryMap = toQueryMap(value);template = addQueryMapQueryParameters(queryMap, template);}if (metadata.headerMapIndex() != null) {template =addHeaderMapHeaders((Map<String, Object>) argv[metadata.headerMapIndex()], template);}return template;}