疫情现在比较稳定了,小区楼下每天该遛狗的遛狗、该买菜的买菜、该逛街的逛街。然而我眉头一皱,现在还是得紧绷神经、严守家里,打好攻坚防疫战(真的不是我宅)。上篇Ribbon的文章,朋友反馈还不错,今天又来挖新坑了。本文对Feign声明式服务调用进行简单分析(参考了翟永超[程序猿DD])的《Spring Cloud微服务实战》)
参考文章:
深入理解Feign之源码解析
Spring Cloud Feign设计原理
SpringCloud | SpringCloud Feign的前世今生【源码深入分析】
上篇分析Ribbon讲到,一般会使用它对RestTemplate的请求拦截来实现对依赖服务的接口调用,而RestTemplate已经实现了对HTTP请求的封装处理,形成了一套模板化的调用方法。实际开发中,对服务依赖的调用肯定不止一处,再加上RestTemplate的封装,几乎每一次调用都是重复简单的模板化内容。Spring Cloud Feign应运而生,它在此基础上做了更进一步的封装,由它来定义实现依赖服务接口。高度概括就是,Feign封装了Http调用流程,更符合面向接口开发的习惯。
在Spring Cloud Feign的实现下,只需创建接口并通过注解的方式来配置它,即可完成对服务提供方的接口绑定,从而简化了在使用Spring Cloud Ribbon时自行封装服务调用客户端的开发量。Feign具备可插拔的注解支持,包括Feign注解和JAX-RS注解。并且还扩展了对Spring MVC的注解支持,对习惯Spring MVC的开发者非常友好。另外,Feign自身一些主要组件,比如解码器和编码器等,也以可插拔的方式提供,需要的时候可以方便更换或扩展。
对Feign大致了解之后,本文就以下方面进行源码分析:
- 包扫描@FeignClient注解的类,获取相关信息注入IOC容器中
- 通过JDK代理生成具体的RequestTemplate,RequestTemplate再生成Request
- Client处理Request
- Client结合Ribbon负载均衡
1、FeignClientsRegistrar源码
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
registerDefaultConfiguration(metadata, registry);
registerFeignClients(metadata, registry);
}
启动带有@EnableFeignClients注解的项目类,会进入到FeignClientsRegistrar类中的registerBeanDefinitions方法,可以看到其中调用了registerDefaultConfiguration(注册默认配置)和registerFeignClients(扫描Feign客户端)
private void registerDefaultConfiguration(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
Map defaultAttrs = metadata
.getAnnotationAttributes(EnableFeignClients.class.getName(), true);
if (defaultAttrs != null && defaultAttrs.containsKey("defaultConfiguration")) {
String name;
if (metadata.hasEnclosingClass()) {
name = "default." + metadata.getEnclosingClassName();
}
else {
name = "default." + metadata.getClassName();
}
registerClientConfiguration(registry, name,
defaultAttrs.get("defaultConfiguration"));
}
}
FeignClientsRegistrar类中的registerDefaultConfiguration函数会检查是否有@EnableFeignClients注解,如果有,则调用registerClientConfiguration方法,注册客户端默认配置。
private void registerClientConfiguration(BeanDefinitionRegistry registry, Object name,
Object configuration) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder
.genericBeanDefinition(FeignClientSpecification.class);
builder.addConstructorArgValue(name);
builder.addConstructorArgValue(configuration);
registry.registerBeanDefinition(
name + "." + FeignClientSpecification.class.getSimpleName(),
builder.getBeanDefinition());
}
registerClientConfiguration方法将bean配置类包装成FeignClientSpecification类,注入到IOC容器中。划个小重点,这个方法非常重要,它包括了FeignClient中的重试策略、超时策略、日志等配置。如果某个服务没有配置,则采用默认配置。
接着,来看下扫描FeignClient。
public void registerFeignClients(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
ClassPathScanningCandidateComponentProvider scanner = getScanner();
scanner.setResourceLoader(this.resourceLoader);
Set basePackages;
Map attrs = metadata
.getAnnotationAttributes(EnableFeignClients.class.getName());
AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(
FeignClient.class);
final Class>[] clients = attrs == null ? null
: (Class>[]) attrs.get("clients");
if (clients == null || clients.length == 0) {
scanner.addIncludeFilter(annotationTypeFilter);
basePackages = getBasePackages(metadata);
}
else {
final Set clientClasses = new HashSet<>();
basePackages = new HashSet<>();
for (Class> clazz : clients) {
basePackages.add(ClassUtils.getPackageName(clazz));
clientClasses.add(clazz.getCanonicalName());
}
AbstractClassTestingTypeFilter filter = new AbstractClassTestingTypeFilter() {
@Override
protected boolean match(ClassMetadata metadata) {
String cleaned = metadata.getClassName().replaceAll("\\$", ".");
return clientClasses.contains(cleaned);
}
};
scanner.addIncludeFilter(
new AllTypeFilter(Arrays.asList(filter, annotationTypeFilter)));
}
for (String basePackage : basePackages) {
Set candidateComponents = scanner
.findCandidateComponents(basePackage);
for (BeanDefinition candidateComponent : candidateComponents) {
if (candidateComponent instanceof AnnotatedBeanDefinition) {
// verify annotated class is an interface
AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;
AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();
Assert.isTrue(annotationMetadata.isInterface(),
"@FeignClient can only be specified on an interface");
Map attributes = annotationMetadata
.getAnnotationAttributes(
FeignClient.class.getCanonicalName());
String name = getClientName(attributes);
registerClientConfiguration(registry, name,
attributes.get("configuration"));
registerFeignClient(registry, annotationMetadata, attributes);
}
}
}
}
registerFeignClients(这个方法有加s)方法扫描被@FeignClient注解修饰的接口。将注解的信息annotationMetadata取出,包括类名,一并赋给beanDefinitionBuilder,再生成beanDefinition,注入到IOC容器中。
registerFeignClients(这个方法有加s)方法继续走下去,会执行registerFeignClient(这个方法没有加s)方法。
private void registerFeignClient(BeanDefinitionRegistry registry,
AnnotationMetadata annotationMetadata, Map attributes) {
String className = annotationMetadata.getClassName();
BeanDefinitionBuilder definition = BeanDefinitionBuilder
.genericBeanDefinition(FeignClientFactoryBean.class);
validate(attributes);
definition.addPropertyValue("url", getUrl(attributes));
definition.addPropertyValue("path", getPath(attributes));
String name = getName(attributes);
definition.addPropertyValue("name", name);
definition.addPropertyValue("type", className);
definition.addPropertyValue("decode404", attributes.get("decode404"));
definition.addPropertyValue("fallback", attributes.get("fallback"));
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
String alias = name + "FeignClient";
AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
beanDefinition.setPrimary(true);
BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
new String[] { alias });
BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
}
registerFeignClient(这个方法没有加s)中有一句代码要划下重点。
BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(FeignClientFactoryBean.class);
很明显,扫描出来的注解信息赋于BeanDefinitionBuilder,同时BeanDefinitionBuilder为FeignClientFactoryBean类型,FeignClientFactoryBean又继承FactoryBean。可推理出,FeignClient其实是用Spring代理工厂来生成代理类。
以上,扫描结束。
2.ReflectiveFeign源码
public T newInstance(Target target) {
Map nameToHandler = targetToHandlersByName.apply(target);
Map methodToHandler = new LinkedHashMap();
List defaultMethodHandlers = new LinkedList();
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;
}
注入Bean之后,ReflectiveFeign中根据接口类和Contract协议解析方式,解析接口类上的方法和注解,转换成内部的MethodHandler处理方式,再将所有请求(已处理为MethodHandler)转换给InvocationHandler,再通过JDK代理,将InvocationHandler动态生成代理实例。
紧接着,刚刚处理的代理实例会被SynchronousMethodHandler类进行拦截处理。
@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;
}
}
}
从源码可以看出,被拦截之后,其中参数会被处理成RequestTemplate,接着调用executeAndDecode方法
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);
} 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.create(response.status(), response.reason(), response.headers(), bodyData);
}
if (response.status() >= 200 && response.status() < 300) {
if (void.class == metadata.returnType()) {
return null;
} else {
return decode(response);
}
} else if (decode404 && response.status() == 404) {
return decoder.decode(response, metadata.returnType());
} 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());
}
}
}
executeAndDecode方法简单概括就两句
Request request = targetRequest(template)
response = client.execute(request, options);
通过RequestTemplate生成Request,再用Client执行获取Response
3、Client源码
Client组件是非常重要的部分,Feign最终发送Request以及接收Response都是在Client中完成的。Client实现中的Default方法由HttpURLConnnection实现网络请求,同时还支持HttpClient、Okhttp。这些都可以配置文件中进行更换。
本节就分析Client其中一个实现FeignRibbonClient,先从它的自动配置类FeignRibbonClientAutoConfiguration下手
@Bean
@ConditionalOnMissingBean
public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
SpringClientFactory clientFactory) {
return new LoadBalancerFeignClient(new Client.Default(null, null),
cachingFactory, clientFactory);
}
FeignRibbonClientAutoConfiguration中feignClient实现的是LoadBalancerFeignClient类。源码中Client.Default采用默认配置,即用HttpURLConnnection网络请求框架。
4、LoadBalancerFeignClient源码
@Override
public Response execute(Request request, Request.Options options) throws IOException {
try {
URI asUri = URI.create(request.url());
String clientName = asUri.getHost();
URI uriWithoutHost = cleanUrl(request.url(), clientName);
FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest(
this.delegate, request, uriWithoutHost);
IClientConfig requestConfig = getClientConfig(options, clientName);
return lbClient(clientName).executeWithLoadBalancer(ribbonRequest,
requestConfig).toResponse();
}
catch (ClientException e) {
IOException io = findIOException(e);
if (io != null) {
throw io;
}
throw new RuntimeException(e);
}
}
源码中FeignClient将Request封装成RibbonRequest,再执行executeWithLoadBalancer方法。
public T executeWithLoadBalancer(final S request, final IClientConfig requestConfig) throws ClientException {
RequestSpecificRetryHandler handler = getRequestSpecificRetryHandler(request, requestConfig);
LoadBalancerCommand command = LoadBalancerCommand.builder()
.withLoadBalancerContext(this)
.withRetryHandler(handler)
.withLoadBalancerURI(request.getUri())
.build();
try {
return command.submit(
new ServerOperation() {
@Override
public Observable call(Server server) {
URI finalUri = reconstructURIWithServer(server, request.getUri());
S requestForServer = (S) request.replaceUri(finalUri);
try {
return Observable.just(AbstractLoadBalancerAwareClient.this.execute(requestForServer, requestConfig));
}
catch (Exception e) {
return Observable.error(e);
}
}
})
.toBlocking()
.single();
} catch (Exception e) {
Throwable t = e.getCause();
if (t instanceof ClientException) {
throw (ClientException) t;
} else {
throw new ClientException(e);
}
}
}
很明显,是通过ribbon负载均衡的方式处理Request请求,并返回Response响应。跟进去最后一步command.submit。里面有段关键的代码:
// Use the load balancer
Observable o =
(server == null ? selectServer() : Observable.just(server))
.concatMap(new Func1>() {
\\以下省略
再跟进去selectServer的代码:
private Observable selectServer() {
return Observable.create(new OnSubscribe() {
@Override
public void call(Subscriber super Server> next) {
try {
Server server = loadBalancerContext.getServerFromLoadBalancer(loadBalancerURI, loadBalancerKey);
next.onNext(server);
next.onCompleted();
} catch (Exception e) {
next.onError(e);
}
}
});
}
从源码中,可以很明显看出,调用了loadBalancerContext负载均衡客户端中选择服务,接下去的流程也就是上篇Ribbon的内容了。
简单概括下Feign的实现过程:
- 首先开启@EnableFeignClients注解,再根据Feign规则,用@FeignClient修饰接口;
- 程序启动后,会进行包扫描,检查所有被@FeignClient修饰的接口,获取注解等信息,并注入到IOC容器中;
- 当接口被调用时,通过JDK代理,生成具体的RequestTemplate,再execute和Decode生成Request;
- Request交给Client处理并返回Response响应;
- Client被封装为LoadBalanceClient类,该类结合Ribbon实现负载均衡。
Feign源码分析就到这里了,本文知识点较为抽象、信息量比较大,读者需要多花些心思去阅读,再加上调试源码加深理解。后面可能会不定期更新,有兴趣的朋友可以在评论区一起讨论研究。
最后有件很重要的事,那就是麻烦点赞关注赞赏,谢谢(๑•̀ㅂ•́)و✧