OpenFegin源码解析图
① BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(FeignClientFactoryBean.class);
Spring Cloud FengnClient实际上是利用Spring的代理工厂来生成代理类，所以在这里地方才会把所有的FeignClient的BeanDefinition设置为FeignClientFactoryBean类型，而
FeignClientFactoryBean继承自FactoryBean，它是一个工厂Bean。在Spring中，FactoryBean是一个工厂Bean，用来创建代理Bean。工厂 Bean 是一种特殊的 Bean, 对于 Bean 的消费者来说，
他逻辑上是感知不到这个 Bean 是普通的 Bean 还是工厂 Bean, 只是按照正常的获取 Bean 方式去调用， 但工厂bean 最后返回的实例不是工厂Bean 本身， 而是执行工厂 Bean 的 getObject 逻辑返回的示例。
② ## ReflectiveFeign.newInstance
Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();
FeignClientsRegistrar
- registerDefaultConfiguration 方法内部从 SpringBoot 启动类上检查是否有@EnableFeignClients, 有该注解的话， 则完成 Feign 框架相关的一些配置内容注册
- registerFeignClients 方法内部从 classpath 中， 扫描获得 @FeignClient 修饰的类， 将类的内容解析为 BeanDefinition , 最终通过调用 Spring 框架中的BeanDefinitionReaderUtils.resgisterBeanDefinition
将解析处理过的 FeignClientBeanDeifinition 添加到 spring 容器中.
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata,BeanDefinitionRegistry registry) {
//注册@EnableFeignClients中定义defaultConfiguration属性下的类，包装成FeignClientSpecification，注册到Spring容器。
//在@FeignClient中有一个属性：configuration，这个属性是表示各个FeignClient自定义的配置类，后面也会通过调用registerClientConfiguration方法来注册成FeignClientSpecification到容器。
//所以，这里可以完全理解在@EnableFeignClients中配置的是做为兜底的配置，在各个@FeignClient配置的就是自定义的情况。
registerDefaultConfiguration(metadata, registry);
registerFeignClients(metadata, registry);
}
FeignClientFactoryBean.getObject
getObject调用的是getTarget方法，它从applicationContext取出FeignContext，FeignContext继承了NamedContextFactory，它是用来来统一维护feign中各个feign客户端相互隔离的上下文。
// FeignContext注册到容器是在FeignAutoConfiguration上完成的
@Autowired(required = false)
private List<FeignClientSpecification> configurations = new ArrayList<>();
@Bean
public FeignContext feignContext() {
FeignContext context = new FeignContext();
context.setConfigurations(this.configurations);
return context;
}
//在初始化FeignContext时，会把configurations在容器中放入FeignContext中。configurations的来源就是在前面registerFeignClients方法中将@FeignClient的配置configuration。
Target.target()
//配置完Feign.Builder之后，再判断是否需要LoadBalance，如果需要，则通过LoadBalance的方法来设置。实际上他们最终调用的是Target.target()方法。
@Override
public Object getObject() throws Exception {
return getTarget();
}
<T> T getTarget() {
FeignContext context = this.applicationContext.getBean(FeignContext.class);
Feign.Builder builder = feign(context);
//如果url为空，则走负载均衡，生成有负载均衡功能的代理类
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));
}
//如果指定了url，则生成默认的代理类
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 unwrap
client = ((LoadBalancerFeignClient) client).getDelegate();
}
if (client instanceof FeignBlockingLoadBalancerClient) {
// not load balancing because we have a url,
// but Spring Cloud LoadBalancer is on the classpath, so unwrap
client = ((FeignBlockingLoadBalancerClient) client).getDelegate();
}
builder.client(client);
}
//生成默认代理类
Targeter targeter = get(context, Targeter.class);
return (T) targeter.target(this, builder, context, new HardCodedTarget<>(this.type, this.name, url));
}
loadBalance
生成具备负载均衡能力的feign客户端，为feign客户端构建起绑定负载均衡客户端Client client = (Client)this.getOptional(context, Client.class);
从上下文中获取一个Client，默认是LoadBalancerFeignClient。它是在FeignRibbonClientAutoConfiguration这个自动装配类中，通过Import实现的
@Import({ HttpClientFeignLoadBalancedConfiguration.class,
OkHttpFeignLoadBalancedConfiguration.class,
DefaultFeignLoadBalancedConfiguration.class })
protected <T> T loadBalance(Feign.Builder builder, FeignContext context, HardCodedTarget<T> target) {
Client client = getOptional(context, Client.class);
if (client != null) {
builder.client(client);
Targeter targeter = get(context, Targeter.class);
return targeter.target(this, builder, context, target);
}
throw new IllegalStateException("No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-netflix-ribbon?");
}
targetToHandlersByName.apply(target)
根据Contract协议规则，解析接口类的注解信息，解析成内部表现：
targetToHandlersByName.apply(target);会解析接口方法上的注解，从而解析出方法粒度的特定的配置信息，然后生产一个SynchronousMethodHandler 然后需要维护一个<method，MethodHandler>的map，放入InvocationHandler的实现FeignInvocationHandler中。
public Map<String, MethodHandler> apply(Target target) {
List<MethodMetadata> metadata = contract.parseAndValidateMetadata(target.type());
Map<String, MethodHandler> result = new LinkedHashMap<String, MethodHandler>();
for (MethodMetadata md : metadata) {
BuildTemplateByResolvingArgs buildTemplate;
if (!md.formParams().isEmpty() && md.template().bodyTemplate() == null) {
buildTemplate =
new BuildFormEncodedTemplateFromArgs(md, encoder, queryMapEncoder, target);
} else if (md.bodyIndex() != null) {
buildTemplate = new BuildEncodedTemplateFromArgs(md, encoder, queryMapEncoder, target);
} else {
buildTemplate = new BuildTemplateByResolvingArgs(md, queryMapEncoder, target);
}
if (md.isIgnored()) {
result.put(md.configKey(), args -> {
throw new IllegalStateException(md.configKey() + " is not a method handled by feign");
});
} else {
result.put(md.configKey(),
factory.create(target, md, buildTemplate, options, decoder, errorDecoder));
}
}
return result;
}
}
SpringMvcContract
当前Spring Cloud 微服务解决方案中，为了降低学习成本，采用了Spring MVC的部分注解来完成 请求协议解析，也就是说 ，写客户端请求接口和像写服务端代码一样：客户端和服务端可以通过SDK的方式进行约定，客户端只需要引入服务端发布的SDK API，就可以使用面向接口的编码方式对接服务。
OpenFeign调用过程
OpenFeign最终返回的是一个#ReflectiveFeign.FeignInvocationHandler的对象。
那么当客户端发起请求时，会进入到FeignInvocationHandler.invoke方法中，它是一个动态代理的实现。
而接着，在invoke方法中，会调用 this.dispatch.get(method)).invoke(args) 。this.dispatch.get(method) 会返回一个SynchronousMethodHandler,进行拦截处理。
这个方法会根据参数生成完成的RequestTemplate对象，这个对象是Http请求的模版，代码如下。
@Override
public Object invoke(Object[] argv) throws Throwable {
RequestTemplate template = buildTemplateFromArgs.create(argv);
Options options = findOptions(argv);
Retryer retryer = this.retryer.clone();
while (true) {
try {
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;
}
}
}
动态生成Request
executeAndDecode
我们已经将restTemplate拼装完成，上面的代码中有一个 executeAndDecode() 方法，该方法通过RequestTemplate生成Request请求对象，然后利用Http Client获取response，来获取响应信息。
Object executeAndDecode(RequestTemplate template, Options options) throws Throwable {
//转化为http请求报文
Request request = targetRequest(template);
if (logLevel != Logger.Level.NONE) {
logger.logRequest(metadata.configKey(), logLevel, request);
}
Response response;
long start = System.nanoTime();
try {
//发起远程通信
response = client.execute(request, options);
// 返回结果
response = response.toBuilder()
.request(request)
.requestTemplate(template)
.build();
} catch (IOException e) {
if (logLevel != Logger.Level.NONE) {
logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime(start));
}
throw errorExecuting(request, e);
}
long elapsedTime = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);
boolean shouldClose = true;
try {
if (logLevel != Logger.Level.NONE) {
response =
logger.logAndRebufferResponse(metadata.configKey(), logLevel, response, elapsedTime);
}
if (Response.class == metadata.returnType()) {
if (response.body() == null) {
return response;
}
if (response.body().length() == null ||
response.body().length() > MAX_RESPONSE_BUFFER_SIZE) {
shouldClose = false;
return response;
}
// Ensure the response body is disconnected
byte[] bodyData = Util.toByteArray(response.body().asInputStream());
return response.toBuilder().body(bodyData).build();
}
if (response.status() >= 200 && response.status() < 300) {
if (void.class == metadata.returnType()) {
return null;
} else {
Object result = decode(response);
shouldClose = closeAfterDecode;
return result;
}
} else if (decode404 && response.status() == 404 && void.class != metadata.returnType()) {
Object result = decode(response);
shouldClose = closeAfterDecode;
return result;
} else {
throw errorDecoder.decode(metadata.configKey(), response);
}
} catch (IOException e) {
if (logLevel != Logger.Level.NONE) {
logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime);
}
throw errorReading(request, response, e);
} finally {
if (shouldClose) {
ensureClosed(response.body());
}
}
}
Client.execute
默认采用JDK的 HttpURLConnection 发起远程调用
@Override
public Response execute(Request request, Options options) throws IOException {
HttpURLConnection connection = convertAndSend(request, options);
return convertResponse(connection, request);
}
Response convertResponse(HttpURLConnection connection, Request request) throws IOException {
int status = connection.getResponseCode();
String reason = connection.getResponseMessage();
if (status < 0) {
throw new IOException(format("Invalid status(%s) executing %s %s", status,
connection.getRequestMethod(), connection.getURL()));
}
Map<String, Collection<String>> headers = new LinkedHashMap<>();
for (Map.Entry<String, List<String>> field : connection.getHeaderFields().entrySet()) {
// response message
if (field.getKey() != null) {
headers.put(field.getKey(), field.getValue());
}
}
Integer length = connection.getContentLength();
if (length == -1) {
length = null;
}
InputStream stream;
if (status >= 400) {
stream = connection.getErrorStream();
} else {
stream = connection.getInputStream();
}
return Response.builder()
.status(status)
.reason(reason)
.headers(headers)
.request(request)
.body(stream, length)
.build();
}