說明
在上篇博文《OpenFeign學習(八):Spring Cloud OpenFeign的加載配置原理》中,我簡單介紹了Spring Cloud 是如何通過註解對Feign Client進行加載配置的。主要介紹了通過FeignClientsRegistrar類,對所有使用@FeignClient註解的類進行加載配置,實現Feign Client的配置類Bean的註冊和相對應Client的FeignClientFactoryBean的註冊。同時還提到在spring.factories配置文件中,配置了有關自動裝配的類FeignRibbonClientAutoConfiguration和FeignAutoConfiguration等類。在本篇博文中,我將繼續通過源碼學習介紹Spring Cloud OpenFeign的加載配置原理。
正文
通過上篇博文我們知道了對Feign Client進行掃描註冊的實際爲其對應的FeignClientFactoryBean,beanName爲@FeignClient作用接口類的ClassName。
接下來,我們瞭解下FeignRibbonClientAutoConfiguration類的作用:
FeignRibbonClientAutoConfiguration
該類從名稱可知屬於RibbonClient的支持類,
@ConditionalOnClass({ILoadBalancer.class, Feign.class})
@Configuration
@AutoConfigureBefore({FeignAutoConfiguration.class})
@EnableConfigurationProperties({FeignHttpClientProperties.class})
@Import({HttpClientFeignLoadBalancedConfiguration.class, OkHttpFeignLoadBalancedConfiguration.class, DefaultFeignLoadBalancedConfiguration.class})
public class FeignRibbonClientAutoConfiguration {
}
通過源碼可以看到,該類作用的前提是類路徑中必需包含了ILoadBalancer類和Feign類,而ILoadBalancer類屬於com.netflix.loadbalancer包,則證明類路徑必須存在Netflix Ribbon的相關依賴。通過該類將會在FeignAutoConfiguration類前加載。
同時通過@EnableConfigurationProperties註解將FeignHttpClientProperties配置類進行注入,該類爲FeignHttpClient的配置類。接着通過@Import註解分別引入了HttpClientFeignLoadBalancedConfiguration,OkHttpFeignLoadBalancedConfiguration,DefaultFeignLoadBalancedConfiguration類,顧名思義,這些類爲不同類型LoadBalancerClient的配置類。
可以看到,該類的作用主要是引入不同配置類,在創建cleint時,根據不同的配置創建不同的feignClient。
關於feignClient的創建,官方文檔對此有以下描述:
if Ribbon is in the classpath and is enabled it is a LoadBalancerFeignClient, otherwise if Spring Cloud LoadBalancer is in the classpath, FeignBlockingLoadBalancerClient is used. If none of them is in the classpath, the default feign client is used.
在創建feignClient時,不同的client優先級爲LoadBalancerFeignClient > FeignBlockingLoadBalancerClient > Default Feign Client 。
而且spring-cloud-starter-openfeign同時包含了spring-cloud-starter-netflix-ribbon和spring-cloud-starter-loadbalancer依賴。
由此可知,默認創建的feignClient都爲LoadBalancerFeignClient類型。
我們可以通過設置feign.okhttp.enabled或feign.httpclient.enabled爲ture來選擇不同的client,但前提是必須引入相關依賴。
FeignAutoConfiguration
該類作用於FeignRibbonClientAutoConfiguration之後,與之類似,爲FeignClient引入註冊相關配置。
@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;
}
....
}
通過源碼可以看到,該類通過@EnableConfigurationProperties註解注入了FeignClientProperties和FeignHttpClientProperties配置類。在其內部,注入了FeignClientSpecification集合,配置了FeignContext,還有對OkHttpClient, ApacheHttpClient,HystrixFeign的相關配置。這裏我們重點關注以上所顯示的代碼相關配置。
通過上篇博文我們可以知道,在註冊時對在@EnableFeignClients註解中配置的defaultConfiguration和在@FeignClient註解中配置的configuration都會註冊爲FeignClientSpecification類型的bean。
在該類中,通過對FeignClientSpecificatio類型的List集合進行自動裝配,將之前註冊的配置類注入到該類中。同時,在實例化FeignContext類型的bean時,將其設置到上下文中。(有關集合的自動裝配請看:https://blog.csdn.net/tales522/article/details/89683282)
配置類FeignClientProperties爲獲取feign.client前綴的配置值,對不同的client進行配置則在前綴後加指定的clientName,對所有client的默認配置則加default(i.e. feign.client.default)。
配置類FeignHttpClientProperties則爲獲取httpclient的配置值。配置前綴爲feign.httpclient。
FeignClientFactoryBean
在使用feignClient時,我們會使用@Autowired註解進行自動裝配依賴注入。此時,會通過factoryBean的getObject()方法獲取對應類的實例對象。
接下來,通過源碼來了解如何創建Feign Client:
public Object getObject() throws Exception {
return this.getTarget();
}
<T> T getTarget() {
// 獲取Feign上下文
FeignContext context = (FeignContext)this.applicationContext.getBean(FeignContext.class);
// 根據上下文創建FeignClient的構造器
Builder builder = this.feign(context);
// 創建對應的client
if (!StringUtils.hasText(this.url)) {
if (!this.name.startsWith("http")) {
this.url = "http://" + this.name;
} else {
this.url = this.name;
}
this.url = this.url + this.cleanPath();
return this.loadBalance(builder, context, new HardCodedTarget(this.type, this.name, this.url));
} else {
if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
this.url = "http://" + this.url;
}
String url = this.url + this.cleanPath();
Client client = (Client)this.getOptional(context, Client.class);
if (client != null) {
if (client instanceof LoadBalancerFeignClient) {
client = ((LoadBalancerFeignClient)client).getDelegate();
}
builder.client(client);
}
Targeter targeter = (Targeter)this.get(context, Targeter.class);
return targeter.target(this, builder, context, new HardCodedTarget(this.type, this.name, url));
}
}
通過源碼可以看出,在getTarget()方法中主要分爲三步來創建feignClient:
- 獲取Feign的上下文對象 FeignContext
- 根據上下文創建FeignClient的構造器
- 根據是否配置url來創建對應的client
FeignContext
通過上面的介紹我們已經知道在FeignAutoConfiguration類中已經聲明配置了對應的Bean。在實例化時,創建對象後爲其設置了cleint的配置類集合。
@Bean
public FeignContext feignContext() {
FeignContext context = new FeignContext();
context.setConfigurations(this.configurations);
return context;
}
public class FeignContext extends NamedContextFactory<FeignClientSpecification> {
public FeignContext() {
super(FeignClientsConfiguration.class, "feign", "feign.client.name");
}
}
FeignContext繼承自NamedContextFactory類,默認構造函數調用了父類的構造函數,其中參數FeignClientsConfiguration類爲Spring Cloud Netflix爲Client提供的默認配置類。
FeignClientsConfiguration.class is the default configuration provided by Spring Cloud Netflix.
FeignClientsConfiguration提供了一些Feign Client的默認配置,如Decoder,Encoder,Contract,Retryer等。
我們已經知道Spring Cloud對OpenFeign的集成使其支持SpringMVC註解及Spring Web的HttpMessageConverters。而這些配置,正是由FeignClientsConfiguration配置類進行聲明配置的。
@Bean
@ConditionalOnMissingBean
public Decoder feignDecoder() {
return new OptionalDecoder(new ResponseEntityDecoder(new SpringDecoder(this.messageConverters)));
}
@Bean
@ConditionalOnMissingBean
@ConditionalOnMissingClass({"org.springframework.data.domain.Pageable"})
public Encoder feignEncoder() {
return new SpringEncoder(this.messageConverters);
}
@Bean
@ConditionalOnMissingBean
public Contract feignContract(ConversionService feignConversionService) {
return new SpringMvcContract(this.parameterProcessors, feignConversionService);
}
可以看到SpringCloud用ResponseEntityDecoder作爲默認Decoder, SpringEncoder作爲默認Encoder,SpringMvcContract代替了OpenFeign默認的Contract,使其能支持SpringMVC的註解。
在SpringEncoder源碼中,可以看到其已經配置生成了SpringFormEncoder對象,所以在表單提交或者文件傳輸時,不用再手動配置SpringFormEncoder。
public class SpringEncoder implements Encoder {
private static final Log log = LogFactory.getLog(SpringEncoder.class);
private final SpringFormEncoder springFormEncoder = new SpringFormEncoder();
private ObjectFactory<HttpMessageConverters> messageConverters;
public SpringEncoder(ObjectFactory<HttpMessageConverters> messageConverters) {
this.messageConverters = messageConverters;
}
.....
}
Builder
接下來通過Feign上下文創建Client構造器對象。
Builder builder = this.feign(context);
protected Builder feign(FeignContext context) {
FeignLoggerFactory loggerFactory = (FeignLoggerFactory)this.get(context, FeignLoggerFactory.class);
// 生成logger 默認仍爲Slf4jLogger
Logger logger = loggerFactory.create(this.type);
// 從AnnotationConfigApplicationContext獲取對應配置
Builder builder = ((Builder)this.get(context, Builder.class)).logger(logger).encoder((Encoder)this.get(context, Encoder.class)).decoder((Decoder)this.get(context, Decoder.class)).contract((Contract)this.get(context, Contract.class));
// 配置其他參數
this.configureFeign(context, builder);
return builder;
}
首先獲取FeignLoggerFactory對象,但是在獲取時,先生成了對應client的AnnotationConfigApplicationContext,並根據之前註解中的配置類進行配置。
protected <T> T get(FeignContext context, Class<T> type) {
T instance = context.getInstance(this.contextId, type);
if (instance == null) {
throw new IllegalStateException("No bean found of type " + type + " for " + this.contextId);
} else {
return instance;
}
}
public <T> T getInstance(String name, Class<T> type) {
// 根據contextId配置生成對應的AnnotationConfigApplicationContext
AnnotationConfigApplicationContext context = this.getContext(name);
return BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context, type).length > 0 ? context.getBean(type) : null;
}
protected AnnotationConfigApplicationContext getContext(String name) {
// 每個client對應context都是單例,這裏使用了雙重檢查加鎖
if (!this.contexts.containsKey(name)) {
synchronized(this.contexts) {
if (!this.contexts.containsKey(name)) {
this.contexts.put(name, this.createContext(name));
}
}
}
return (AnnotationConfigApplicationContext)this.contexts.get(name);
}
創建AnnotationConfigApplicationContext時,首先獲取註冊client對應配置的configuration,然後再註冊client的默認配置,最後註冊defaultConfigType,也就是Spring Cloud Netflix提供的默認配置類FeignClientsConfiguration。
protected AnnotationConfigApplicationContext createContext(String name) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
// 獲取client對應的配置類進行註冊
if (this.configurations.containsKey(name)) {
Class[] var3 = ((NamedContextFactory.Specification)this.configurations.get(name)).getConfiguration();
int var4 = var3.length;
for(int var5 = 0; var5 < var4; ++var5) {
Class<?> configuration = var3[var5];
context.register(new Class[]{configuration});
}
}
Iterator var9 = this.configurations.entrySet().iterator();
// 循環註冊所有默認的以default開頭的配置
while(true) {
Entry entry;
do {
// 最後註冊配置類FeignClientsConfiguration
if (!var9.hasNext()) {
context.register(new Class[]{PropertyPlaceholderAutoConfiguration.class, this.defaultConfigType});
context.getEnvironment().getPropertySources().addFirst(new MapPropertySource(this.propertySourceName, Collections.singletonMap(this.propertyName, name)));
if (this.parent != null) {
context.setParent(this.parent);
context.setClassLoader(this.parent.getClassLoader());
}
context.setDisplayName(this.generateDisplayName(name));
context.refresh();
return context;
}
entry = (Entry)var9.next();
} while(!((String)entry.getKey()).startsWith("default."));
Class[] var11 = ((NamedContextFactory.Specification)entry.getValue()).getConfiguration();
int var12 = var11.length;
for(int var7 = 0; var7 < var12; ++var7) {
Class<?> configuration = var11[var7];
context.register(new Class[]{configuration});
}
}
}
創建完成client對應的AnnotationConfigApplicationContext後,根據配置類創建生成構建起Builder。通過以上代碼可以看到,從自定義配置類或者默認配置類中,可以獲取先進行配置的有Logger,Encoder,Decoder, Contract。
Builder builder = ((Builder)this.get(context, Builder.class)).logger(logger).encoder((Encoder)this.get(context, Encoder.class)).decoder((Decoder)this.get(context, Decoder.class)).contract((Contract)this.get(context, Contract.class));
之後,在通過configureFeign方法配置client其他參數:
this.configureFeign(context, builder);
protected void configureFeign(FeignContext context, Builder builder) {
// 獲取配置文件中關於client配置的參數
FeignClientProperties properties = (FeignClientProperties)this.applicationContext.getBean(FeignClientProperties.class);
// 按優先級順序進行配置
if (properties != null) {
if (properties.isDefaultToProperties()) {
this.configureUsingConfiguration(context, builder);
this.configureUsingProperties((FeignClientConfiguration)properties.getConfig().get(properties.getDefaultConfig()), builder);
this.configureUsingProperties((FeignClientConfiguration)properties.getConfig().get(this.contextId), builder);
} else {
this.configureUsingProperties((FeignClientConfiguration)properties.getConfig().get(properties.getDefaultConfig()), builder);
this.configureUsingProperties((FeignClientConfiguration)properties.getConfig().get(this.contextId), builder);
this.configureUsingConfiguration(context, builder);
}
} else {
this.configureUsingConfiguration(context, builder);
}
}
通過以上代碼我們可以看到,先獲取了FeignClientProperties示例,該類用來讀取配置文件中有關feign client的配置參數。根據defaultToProperties參數來決定不同的配置順序,對此,官方文檔中也進行了說明:
If we create both @Configuration bean and configuration properties, configuration properties will win. It will override @Configuration values. But if you want to change the priority to @Configuration, you can change feign.client.default-to-properties to false.
可以看到如果同時使用了@Configuration bean 也就是註解中設置了配置類和配置文件配置了相關屬性時,默認情況下,配置文件會覆蓋配置類的值。但是可以通過設置feign.client.default-to-properties 值爲false改變優先級,此參數值對應爲FeignClientProperties的defaultToProperties參數值。
若默認情況,會先根據默認配置類和自定配置類的值進行配置:
this.configureUsingConfiguration(context, builder);
接下來根據配置文件中配置的對所有client的默認值進行配置:
this.configureUsingProperties((FeignClientConfiguration)properties.getConfig().get(properties.getDefaultConfig()), builder);
最後,根據配置文件的自定義參數值進行配置:
this.configureUsingProperties((FeignClientConfiguration)properties.getConfig().get(this.contextId), builder);
當設置爲false時,調換配置順序,將配置類的配置放到最後。
主要配置了Logger.Level,Retryer,ErrorDecoder,RequestInterceptor,decode404及httpclient相關配置。
在FeignClientsConfiguration類,配置了Retryer的bean,默認情況下,Spring Cloud OpenFeign的feignClient不會進行重試,這與原生的OpenFeign有所不同。
@Bean
@ConditionalOnMissingBean
public Retryer feignRetryer() {
return Retryer.NEVER_RETRY;
}
Client
在完成Buidler的創建配置後,根據@FeignClient註解中是否配置了url來完成最終的FeignClient創建。
在未配置時,進行了以下配置:
if (!StringUtils.hasText(this.url)) {
if (!this.name.startsWith("http")) {
this.url = "http://" + this.name;
} else {
this.url = this.name;
}
// url 值類似爲 http://clientName
this.url = this.url + this.cleanPath();
return this.loadBalance(builder, context, new HardCodedTarget(this.type, this.name, this.url));
}
可以看到調用loadBalance方法進行創建
protected <T> T loadBalance(Builder builder, FeignContext context, HardCodedTarget<T> target) {
Client client = (Client)this.getOptional(context, Client.class);
if (client != null) {
builder.client(client);
Targeter targeter = (Targeter)this.get(context, Targeter.class);
return targeter.target(this, builder, context, target);
} else {
throw new IllegalStateException("No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-netflix-ribbon?");
}
}
在該方法中,獲取了配置的Client對象,上面提到在FeignRibbonClientAutoConfiguration配置類中引入了三個配置類,分別爲HttpClientFeignLoadBalancedConfiguration,OkHttpFeignLoadBalancedConfiguration和DefaultFeignLoadBalancedConfiguration。
要使用 ApacheHttpClient 或 OkHttpClient 時,必須引入對應的依賴,同時配置文件中feign.okhttp.enabled或feign.httpclient.enabled對應值true,否則就使用默認的client。
這裏在DefaultFeignLoadBalancedConfiguration配置類中配置創建了默認的LoadBalancerFeignClient。
@Bean
@ConditionalOnMissingBean
public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory, SpringClientFactory clientFactory) {
return new LoadBalancerFeignClient(new Default((SSLSocketFactory)null, (HostnameVerifier)null), cachingFactory, clientFactory);
}
該默認LoadBalancerFeignClient中delegate即爲feign默認的client,使用的是HttpURLConnection:
public static class Default implements Client {
private final SSLSocketFactory sslContextFactory;
private final HostnameVerifier hostnameVerifier;
public Default(SSLSocketFactory sslContextFactory, HostnameVerifier hostnameVerifier) {
this.sslContextFactory = sslContextFactory;
this.hostnameVerifier = hostnameVerifier;
}
....
}
再獲取對應的Targeter,該接口共有兩個實現類,分別爲DefaultTargeter和HystrixTargeter,這裏獲取默認的DefaultTargeter。
@Configuration
@ConditionalOnMissingClass({"feign.hystrix.HystrixFeign"})
protected static class DefaultFeignTargeterConfiguration {
protected DefaultFeignTargeterConfiguration() {
}
@Bean
@ConditionalOnMissingBean
public Targeter feignTargeter() {
return new DefaultTargeter();
}
}
最後調用feign.target(target)創建對應的代理target。
若配置有url,則進行以下配置:
else {
if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
this.url = "http://" + this.url;
}
String url = this.url + this.cleanPath();
Client client = (Client)this.getOptional(context, Client.class);
if (client != null) {
if (client instanceof LoadBalancerFeignClient) {
client = ((LoadBalancerFeignClient)client).getDelegate();
}
// 獲取最終代理client
builder.client(client);
}
Targeter targeter = (Targeter)this.get(context, Targeter.class);
return targeter.target(this, builder, context, new HardCodedTarget(this.type, this.name, url));
}
由源碼可知,若配置了url,在創建代理時使用的client不是LoadBalancerFeignClient,也就無法實現負載均衡。
至此,FeignClient配置加載創建原理介紹完畢。
總結
通過源碼我們瞭解了Spring Cloud OpenFeign的加載配置創建流程。通過註解@FeignClient和@EnableFeignClients註解實現了client的配置聲明註冊,再通過FeignRibbonClientAutoConfiguration和FeignAutoConfiguration類進行自動裝配。
在通過FeignClientFactoryBean創建client對象時,瞭解了Spring Cloud是如何進行配置,不同配置的優先級順序的選擇,及根據配置生成不同配置類的流程,及Spring Cloud對OpenFeign的集成支持如何實現,及與原生OpenFeign的區別之處。
更多的使用方法及配置請閱讀官方文檔。
接下來,我將繼續學習閱讀源碼,瞭解Ribbon是如何在Spring Cloud OpenFeign中進行負載均衡的。