Feign的使用非常简单，增加如下配置之后，便可以使用Feign进行调用。非常简单是不是。主要的工作由Feign框架完成。业务代码只提供了一个Interface, 然后由Feign动态生成代理类来实现整个的调用过程。
@Configuration
public class FeignConfig {
@Bean(name = "myCient")
public MyClient myClient() {
return Feign.builder().requestInterceptor(new MyRequestInterceptor()).retryer(Retryer.NEVER_RETRY).logLevel(Logger.Level.BASIC).logger(new Slf4jLogger())
.encoder(new JacksonEncoder()).decoder(new JacksonDecoder()).
errorDecoder(new MyResultDecoder()).target(MyClient.class, "serviceUrl");
}
}
框架相关代码：
Feign.java
public Feign build() {
SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =
new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,
logLevel, decode404);
ParseHandlersByName handlersByName =
new ParseHandlersByName(contract, options, encoder, decoder,
errorDecoder, synchronousMethodHandlerFactory);
return new ReflectiveFeign(handlersByName, invocationHandlerFactory);
}
ReflectiveFeign.java
@SuppressWarnings("unchecked")
@Override
public <T> T newInstance(Target<T> target) {
Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target); // 这个方法是重点，生成了代理类具体实现。具体参考SynchronousMethodHandler。
Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();
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);
T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(), new Class<?>[]{target.type()}, handler);
for(DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
defaultMethodHandler.bindTo(proxy);
}
return proxy;
}
SynchronousMethodHandler.java
final class SynchronousMethodHandler implements MethodHandler{
...
//具体实现逻辑，代理类的InvokeHandler的invoke方法会调用这个方法。
@Override
public Object invoke(Object[] argv) throws Throwable {
RequestTemplate template = buildTemplateFromArgs.create(argv);
Retryer retryer = this.retryer.clone();
while (true) {
try {
return executeAndDecode(template);
} catch (RetryableException e) {
retryer.continueOrPropagate(e);
if (logLevel != Logger.Level.NONE) {
logger.logRetry(metadata.configKey(), logLevel);
}
continue;
}
}
}
...
}
原文：https://www.cnblogs.com/lzmrex/p/9466886.html