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在上篇文章 Feign 自动装配中，我们提到了 Feign 的自动装配的原理, 以及 Feign 整合 Ribbon 和 Hystrix 的核心在类 FeignClientFactoryBean 中，那么本篇文章就来揭开这个类的神秘面纱
首先，我们看到这个类实现了 FactoryBean 这个接口，这个接口的主要作用就是利用 getObject() 来创建一些实例化过程比较复杂的 bean，更多关于这个接口的内容可以参考这篇文章：Spring 扩展点之 FactoryBean 接口
我们直接来看这个类的 getObject 方法：
public Object getObject() throws Exception {FeignContext context = applicationContext.getBean(FeignContext.class);
Feign.Builder builder = feign(context);
if (!StringUtils.hasText(this.url)) {
String url;
if (!this.name.startsWith("http")) {url = "http://" + this.name;}
else {url = this.name;}
url += cleanPath();
return loadBalance(builder, context, new HardCodedTarget<>(this.type,
this.name, 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 lod balancing because we have a url,
// but ribbon is on the classpath, so unwrap
client = ((LoadBalancerFeignClient)client).getDelegate();}
builder.client(client);
}
Targeter targeter = get(context, Targeter.class);
return targeter.target(this, builder, context, new HardCodedTarget<>(this.type, this.name, url));
}- 获取 bean:
FeignContext，这个 bean 上篇文章已经说过了。里面包含了各个 Feign 客户端的配置
2. 构建 Feign.Builder
设置编解码器
protected Feign.Builder feign(FeignContext context) {FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
Logger logger = loggerFactory.create(this.type);
Feign.Builder builder = get(context, Feign.Builder.class)
.logger(logger)
.encoder(get(context, Encoder.class))
.decoder(get(context, Decoder.class))
.contract(get(context, Contract.class));
configureFeign(context, builder);
return builder;
}设置日志、重试策略、错误 code 解析、超时时间、拦截器
protected void configureUsingConfiguration(FeignContext context, Feign.Builder builder) {Logger.Level level = getOptional(context, Logger.Level.class);
if (level != null) {builder.logLevel(level);
}
Retryer retryer = getOptional(context, Retryer.class);
if (retryer != null) {builder.retryer(retryer);
}
ErrorDecoder errorDecoder = getOptional(context, ErrorDecoder.class);
if (errorDecoder != null) {builder.errorDecoder(errorDecoder);
}
Request.Options options = getOptional(context, Request.Options.class);
if (options != null) {builder.options(options);
}
Map<String, RequestInterceptor> requestInterceptors = context.getInstances(this.name, RequestInterceptor.class);
if (requestInterceptors != null) {builder.requestInterceptors(requestInterceptors.values());
}
if (decode404) {builder.decode404();
}
}- 判断 Feign 是否指定 url 属性，正常情况下是没有指定 url 的，所以会添加一个 http:// 前缀
4. 获取代理
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?");
}首先获取 Client 的实现类，这个实现类是 LoadBalancerFeignClient, 这个类里融合了 Ribbon 的相关内容。然后将Client 包装到 Feign.Builder 中，接着获取 Targeter，这里我们存在 Hystrix 环境，所以Targeter 的实现类为HystrixTargeter
public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context,
Target.HardCodedTarget<T> target) {if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) {return feign.target(target);
}
feign.hystrix.HystrixFeign.Builder builder = (feign.hystrix.HystrixFeign.Builder) feign;
SetterFactory setterFactory = getOptional(factory.getName(), context,
SetterFactory.class);
if (setterFactory != null) {builder.setterFactory(setterFactory);
}
Class<?> fallback = factory.getFallback();
if (fallback != void.class) {return targetWithFallback(factory.getName(), context, target, builder, fallback);
}
Class<?> fallbackFactory = factory.getFallbackFactory();
if (fallbackFactory != void.class) {return targetWithFallbackFactory(factory.getName(), context, target, builder, fallbackFactory);
}
return feign.target(target);
}接着以 Feign 客户端设置了 fallback 为例
private <T> T targetWithFallback(String feignClientName, FeignContext context,Target.HardCodedTarget<T> target,HystrixFeign.Builder builder, Class<?> fallback) {T fallbackInstance = getFromContext("fallback", feignClientName, context, fallback, target.type());
return builder.target(target, fallbackInstance);
}接着就是这个代理的创建，现在这个代理中包含了 Ribbon 和 Hystrix。而这个代理类的实现类是HystrixInvocationHandler
public Object invoke(final Object proxy, final Method method, final Object[] args)
throws Throwable {
// early exit if the invoked method is from java.lang.Object
// code is the same as ReflectiveFeign.FeignInvocationHandler
if ("equals".equals(method.getName())) {
try {
Object otherHandler =
args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
return equals(otherHandler);
} catch (IllegalArgumentException e) {return false;}
} else if ("hashCode".equals(method.getName())) {return hashCode();
} else if ("toString".equals(method.getName())) {return toString();
}
HystrixCommand<Object> hystrixCommand = new HystrixCommand<Object>(setterMethodMap.get(method)) {
@Override
protected Object run() throws Exception {
try {return HystrixInvocationHandler.this.dispatch.get(method).invoke(args);
} catch (Exception e) {throw e;} catch (Throwable t) {throw (Error) t;
}
}
@Override
protected Object getFallback() {if (fallbackFactory == null) {return super.getFallback();
}
try {Object fallback = fallbackFactory.create(getExecutionException());
Object result = fallbackMethodMap.get(method).invoke(fallback, args);
if (isReturnsHystrixCommand(method)) {return ((HystrixCommand) result).execute();} else if (isReturnsObservable(method)) {
// Create a cold Observable
return ((Observable) result).toBlocking().first();
} else if (isReturnsSingle(method)) {
// Create a cold Observable as a Single
return ((Single) result).toObservable().toBlocking().first();} else if (isReturnsCompletable(method)) {((Completable) result).await();
return null;
} else {return result;}
} catch (IllegalAccessException e) {
// shouldn't happen as method is public due to being an interface
throw new AssertionError(e);
} catch (InvocationTargetException e) {
// Exceptions on fallback are tossed by Hystrix
throw new AssertionError(e.getCause());
}
}
};
if (isReturnsHystrixCommand(method)) {return hystrixCommand;} else if (isReturnsObservable(method)) {
// Create a cold Observable
return hystrixCommand.toObservable();} else if (isReturnsSingle(method)) {
// Create a cold Observable as a Single
return hystrixCommand.toObservable().toSingle();
} else if (isReturnsCompletable(method)) {return hystrixCommand.toObservable().toCompletable();}
return hystrixCommand.execute();}这里就利用到了 Hystrix 的知识，更多关于 Hystrix 的内容可以参考之前的文章
接着深入 invoke 方法
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;
}
}
}这里构建了请求信息和重试策略，具体请求内容在下面：
Object executeAndDecode(RequestTemplate template) throws Throwable {Request request = targetRequest(template);
if (logLevel != Logger.Level.NONE) {logger.logRequest(metadata.configKey(), logLevel, request);
}
Response response;
long start = System.nanoTime();
try {response = client.execute(request, options);
// ensure the request is set. TODO: remove in Feign 10
response.toBuilder().request(request).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);
// ensure the request is set. TODO: remove in Feign 10
response.toBuilder().request(request).build();}
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 {return decode(response);
}
} else if (decode404 && response.status() == 404 && void.class != metadata.returnType()) {return decode(response);
} 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());
}
}
}
再往下深入就是 Ribbon 的负载均衡了，具体内容可以参考之前的文章
正文完
