前言
前情回顧
上一講主要看了@EnableFeignClients中的registerBeanDefinitions()方法，這里面主要是
將EnableFeignClients注解對應的配置屬性注入，將FeignClient注解對應的屬性注入。
最后是生成FeignClient對應的bean，注入到Spring 的IOC容器。
本講目錄
目錄如下：
- registerFeignClient()回顧
- FeignClientFactoryBean.getObject()解析
- Feign.builder()及client()構建邏輯
- 創建Feign動態代理實現細節
說明
原創不易，如若轉載 請標明來源！
博客地址：一枝花算不算浪漫
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源碼分析
registerFeignClient()回顧
回顧下之前的代碼：
private void registerFeignClient(BeanDefinitionRegistry registry,
AnnotationMetadata annotationMetadata, Map<String, Object> 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.addPropertyValue("fallbackFactory", attributes.get("fallbackFactory"));
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
String alias = name + "FeignClient";
AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
boolean primary = (Boolean)attributes.get("primary"); // has a default, won't be null
beanDefinition.setPrimary(primary);
String qualifier = getQualifier(attributes);
if (StringUtils.hasText(qualifier)) {
alias = qualifier;
}
BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
new String[] { alias });
BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
}
在registerFeignClient()方法中構造了一個BeanDefinitionBuilder對象，BeanDefinitionBuilder的主要作用就是構建一個AbstractBeanDefinition，AbstractBeanDefinition類最終被構建成一個BeanDefinitionHolder 然后注冊到Spring中。
beanDefinition類為FeignClientFactoryBean，故在Spring獲取類的時候實際返回的是FeignClientFactoryBean類。
FeignClientFactoryBean作為一個實現了FactoryBean的工廠類，那么每次在Spring Context 創建實體類的時候會調用它的getObject()方法。
FeignClientFactoryBean.getObject()解析
這里直接分析FeignClientFactoryBean.getObject()方法，這里包含着Feign動態代理的原理。
先看下代碼：
@Override
public Object getObject() throws Exception {
// 可以類比於ribbon中的SpringClientFactory，每個服務都對應一個獨立的spring容器
FeignContext context = applicationContext.getBean(FeignContext.class);
// builder中包含contract、logLevel、encoder、decoder、options等信息
Feign.Builder builder = feign(context);
// 如果@FeignClient注解上沒有指定url，說明是要用ribbon的負載均衡
if (!StringUtils.hasText(this.url)) {
String url;
if (!this.name.startsWith("http")) {
url = "http://" + this.name;
}
else {
url = this.name;
}
// 這里構建的url類似於：http://serviceA
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));
}
public <T> T getInstance(String name, Class<T> type) {
// getContext是從SpringClientContext中獲取，之前講ribbon源碼時講過
// 一個serviceName都會有自己的一個SpringClientContext上下文信息
AnnotationConfigApplicationContext context = getContext(name);
if (BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context,
type).length > 0) {
// 這里是獲取到LoadBalancerFeignClient
return context.getBean(type);
}
return null;
}
首先是FeignContext ，我們可以類比下ribbon中的SpringClientFactory, 每個服務的調用，都有一個獨立的ILoadBalancer、IRule、IPing等等，每個服務都對應一個獨立的spring容器，從那個獨立的容器中，可以取出這個服務關聯的屬於自己的LoadBalancer之類的東西。
如果我們調用一個服務的話，比如ServiceA，那么這個服務就會關聯一個spring容器，FeignContext就代表一個獨立的容器，關聯着自己獨立的一些組件，例如Logger組件、Decoder組件、Encoder組件等等。
我們可以看下FeignAutoConfiguration中：
@Configuration
@ConditionalOnClass(Feign.class)
@EnableConfigurationProperties({FeignClientProperties.class, FeignHttpClientProperties.class})
public class FeignAutoConfiguration {
@Bean
public FeignContext feignContext() {
FeignContext context = new FeignContext();
// configurations是一個Map結構
context.setConfigurations(this.configurations);
return context;
}
}
public class FeignContext extends NamedContextFactory<FeignClientSpecification> {
public FeignContext() {
// FeignClientsConfiguration中會加載Encoder、Decoder、Logger等組件
super(FeignClientsConfiguration.class, "feign", "feign.client.name");
}
}
這里可以知道FeignContext的結構，里面其實就是封裝了一個服務實例（ServiceA）對應的各種組件，其中FeignClientsConfiguration是加載默認的組件信息配置類。
接下來還是回到FeignClientFactoryBean.getObject()中，接着看feign()方法：
protected Feign.Builder feign(FeignContext context) {
// 從context中獲取到默認Logger組件：Slf4jLogger
FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
Logger logger = loggerFactory.create(this.type);
// 從context中找type：Feign.Builder.class 對應的組件信息
// 然后往builder中放入各種組件信息
Feign.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:on
configureFeign(context, builder);
return builder;
}
protected <T> T get(FeignContext context, Class<T> type) {
// context中轉載的有Logger組件信息，這里默認的是Slf4jLogger
T instance = context.getInstance(this.name, type);
if (instance == null) {
throw new IllegalStateException("No bean found of type " + type + " for "
+ this.name);
}
return instance;
}
這里是構造一個Feign.builder()對象，里面還是封裝了各種組件信息。其中Feign.builder在FeignClientsConfiguration被初始化，一般使用的是HystrixFeign.builder()
@Configuration
public class FeignClientsConfiguration {
// 一般環境都會配置feign.hystrix.enabled = true，這里直接看HystrixFeign.builder();
@Configuration
@ConditionalOnClass({ HystrixCommand.class, HystrixFeign.class })
protected static class HystrixFeignConfiguration {
@Bean
@Scope("prototype")
@ConditionalOnMissingBean
@ConditionalOnProperty(name = "feign.hystrix.enabled", matchIfMissing = false)
public Feign.Builder feignHystrixBuilder() {
return HystrixFeign.builder();
}
}
}
接着看configureFeign() 方法，這個方法是讀取application.properties中的配置信息。這里有個很有趣的配置：
configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()), builder);
configureUsingProperties(properties.getConfig().get(this.name), builder);
如果我們配置feign，先指定一個全局配置，在指定針對於某個服務的配置，那么某個服務配置的優先級會覆蓋全局的配置。
一張圖總結下Feign.builder()構建的過程：
Feign.builder()及client()構建邏輯
還是接着上面getObject() 方法去分析，上面分析完了Feign.builder()的構建，下面接着看看剩下的代碼。
loadBalance(builder, context, new HardCodedTarget<>(this.type,this.name, url));
這里形式構造了一個HardCodeTarget對象，這個對象包含了接口類型（com.barrywang.service.feign.ServiceAFeignClient）、服務名稱（ServiceA）、url地址（http://ServiceA），跟Feign.Builder、FeignContext，一起，傳入了loadBalance()方法里去。
接着查看loadBalance() 方法：
protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
HardCodedTarget<T> target) {
// 這里還是從context中獲取feignClient數據
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?");
}
protected <T> T getOptional(FeignContext context, Class<T> type) {
return context.getInstance(this.name, type);
}
這里還是從context中獲取Client.class對應的數據，我們繼續查看FeignAutoConfiguration 類，但是並沒有發現Feign.client相關的數據，查看FeignAutoConfiguration的依賴，可以找到FeignRibbonClientAutoConfiguration ，代碼如下：
@ConditionalOnClass({ ILoadBalancer.class, Feign.class })
@Configuration
@AutoConfigureBefore(FeignAutoConfiguration.class)
@EnableConfigurationProperties({ FeignHttpClientProperties.class })
// 這里會import三個FeignLoadBalance配置
@Import({ HttpClientFeignLoadBalancedConfiguration.class,
OkHttpFeignLoadBalancedConfiguration.class,
DefaultFeignLoadBalancedConfiguration.class })
public class FeignRibbonClientAutoConfiguration {
@Bean
@Primary
@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
public CachingSpringLoadBalancerFactory cachingLBClientFactory(
SpringClientFactory factory) {
return new CachingSpringLoadBalancerFactory(factory);
}
@Bean
@Primary
@ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
public CachingSpringLoadBalancerFactory retryabeCachingLBClientFactory(
SpringClientFactory factory,
LoadBalancedRetryPolicyFactory retryPolicyFactory,
LoadBalancedBackOffPolicyFactory loadBalancedBackOffPolicyFactory,
LoadBalancedRetryListenerFactory loadBalancedRetryListenerFactory) {
return new CachingSpringLoadBalancerFactory(factory, retryPolicyFactory, loadBalancedBackOffPolicyFactory, loadBalancedRetryListenerFactory);
}
// Options是超時相關的配置
@Bean
@ConditionalOnMissingBean
public Request.Options feignRequestOptions() {
return LoadBalancerFeignClient.DEFAULT_OPTIONS;
}
}
@Configuration
class DefaultFeignLoadBalancedConfiguration {
@Bean
@ConditionalOnMissingBean
public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
SpringClientFactory clientFactory) {
return new LoadBalancerFeignClient(new Client.Default(null, null),
cachingFactory, clientFactory);
}
}
到了這里就知道了，這里Feign.client默認應該就是LoadBalancerFeignClient了。
到這繼續用一張圖總結下：
創建Feign動態代理實現細節
接着上面代碼，默認Feign.client()為LoadBalancerFeignClient, 然后將client加入到builder中。接着繼續跟進targer相關：
protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
HardCodedTarget<T> target) {
Client client = getOptional(context, Client.class);
if (client != null) {
builder.client(client);
// 這里又是通過Targer然后再context中獲取默認配置
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?");
}
protected <T> T get(FeignContext context, Class<T> type) {
T instance = context.getInstance(this.name, type);
if (instance == null) {
throw new IllegalStateException("No bean found of type " + type + " for "
+ this.name);
}
return instance;
}
可以看到，這里又是通過Targeter.class從context中獲取對應默認Targter。我們繼續通過FeignAutoConfiguration中進行查找：
@Configuration
@ConditionalOnClass(Feign.class)
@EnableConfigurationProperties({FeignClientProperties.class, FeignHttpClientProperties.class})
public class FeignAutoConfiguration {
@Autowired(required = false)
private List<FeignClientSpecification> configurations = new ArrayList<>();
@Bean
public FeignContext feignContext() {
FeignContext context = new FeignContext();
context.setConfigurations(this.configurations);
return context;
}
// 如果配置了feign.hystrix.HystrixFeign 則創建HystrixTargeter
@Configuration
@ConditionalOnClass(name = "feign.hystrix.HystrixFeign")
protected static class HystrixFeignTargeterConfiguration {
@Bean
@ConditionalOnMissingBean
public Targeter feignTargeter() {
return new HystrixTargeter();
}
}
// 如果沒有配置feign.hystrix.HystrixFeign 則創建DefaultTargeter
@Configuration
@ConditionalOnMissingClass("feign.hystrix.HystrixFeign")
protected static class DefaultFeignTargeterConfiguration {
@Bean
@ConditionalOnMissingBean
public Targeter feignTargeter() {
return new DefaultTargeter();
}
}
}
在默認情況下，feign是和hystrix整合的，feign.hystrix.HystrixFeign會有配置，所以這里默認Targeter使用的是HystrixTargeter, 在loadBalance()方法中執行的targeter.target()方法就是執行HystrixTargeter.target()方法：
class HystrixTargeter implements Targeter {
public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context,
Target.HardCodedTarget<T> target) {
// 判斷Feign.builder()類型
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);
}
// 最終都會執行feign.target()方法
return feign.target(target);
}
public abstract class Feign {
public static Builder builder() {
return new Builder();
}
/**
* Returns a new instance of an HTTP API, defined by annotations in the {@link Feign Contract},
* for the specified {@code target}. You should cache this result.
*/
public abstract <T> T newInstance(Target<T> target);
public static class Builder {
// 省略部分代碼
public <T> T target(Target<T> target) {
return build().newInstance(target);
}
public Feign build() {
// 構建一個SynchronousMethodHandler工廠
SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =
new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,
logLevel, decode404);
// 構建
ParseHandlersByName handlersByName =
new ParseHandlersByName(contract, options, encoder, decoder,
errorDecoder, synchronousMethodHandlerFactory);
return new ReflectiveFeign(handlersByName, invocationHandlerFactory);
}
}
}
這里主要是build方法，構造了一個ReflectieFein對象，接着看它里面的newInstance()方法：
@Override
public <T> T newInstance(Target<T> target) {
// nameToHandler是@FeignClient中的方法名對應的MethodHandler對象
Map<String, InvocationHandlerFactory.MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
Map<Method, InvocationHandlerFactory.MethodHandler> methodToHandler = new LinkedHashMap<Method, InvocationHandlerFactory.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 {
// 將具體的method作為map的key值
methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
}
}
// JDK動態代理 返回類似於：ReflectiveFeign$FeignInvocationHandler@7642
// methodToHandler中包含Feign.builder()、Feign.client()等信息
InvocationHandler handler = factory.create(target, methodToHandler);
T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(), new Class<?>[]{target.type()}, handler);
for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
defaultMethodHandler.bindTo(proxy);
}
return proxy;
}
這里就是使用了JDK動態代理，實際上返回的Feign動態代理的對象類似於：ReflectiveFeign$FeignInvocationHandler@7642。
這也和我們第一講中的debug截圖一致了，到了這里feign動態代理對象的生成原理都已經很清楚了。
最后debug一下，看下最終生成的動態代理對象：
總結
最后用一張圖總結Feign動態代理生成的規則：
- 生成Feign.builder(),里面包含Encoder、Decoder、Logger等組件，還有application.properties中相關的feign client配置信息
- 生成Feign.client()，默認為LoadBalancerFeignClient
- 生成默認Targter對象：HystrixTargter
- builder、client、targter 通過JDK動態代理生成feign動態代理對象
一張圖總結：
申明
本文章首發自本人博客：https://www.cnblogs.com/wang-meng 和公眾號：壹枝花算不算浪漫，如若轉載請標明來源!
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