前言
在spring cloud alibaba 中使用OpenFeign，可以用来使用HTTP请求访问远程服务。
一、使用示例
1、 引入依赖；
<!-- https://mvnrepository.com/artifact/org.springframework.cloud/spring-cloud-starter-openfeign -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
<version>3.0.0</version>
</dependency>
2、 启动类；
加上注解@EnableFeignClients
@SpringBootApplication
@EnableFeignClients
public class CloudApplication {
public static void main(String[] args) {
SpringApplication.run(CloudApplication.class, args);
System.out.println("started...");
}
}
3、 创建服务api接口；
用@FeignClient 注解标识，value = “server” 表示要访问的服务提供者的名称是server
@FeignClient(value = "server")
@Component
public interface ServerApi {
@GetMapping("/server/test/{id}")
Map test(@PathVariable String id);
}
4、 Controller接口；
@RestController
@RequestMapping("/client")
public class ClientController {
@Autowired
private ServerApi serverApi;
@GetMapping("/test/{id}")
public Map test(@PathVariable String id){
return serverApi.test(id);
}
}
二、注册FeignClients
1、 @EnableFeignClients；
在启动类上加上了注解@EnableFeignClients，该注解导入了配置类@Import(FeignClientsRegistrar.class)
2、 FeignClientsRegistrar；
实现了ImportBeanDefinitionRegistrar 接口，重写了 registerBeanDefinitions( ) 方法，
在配置类加载过程中，会回调该方法
loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
3、 回调方法；
FeignClientsRegistrar.java
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
//注册默认的配置类
registerDefaultConfiguration(metadata, registry);
//注册feign客户端 FeignClients
registerFeignClients(metadata, registry);
}
4、 注册默认的配置类；
private void registerDefaultConfiguration(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
//获取 @EnableFeignClients 注解信息
Map<String, Object> 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();
}
//注册客户端配置类
registerClientConfiguration(registry, name, defaultAttrs.get("defaultConfiguration"));
}
}
注册FeignClientSpecification 类
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());
}
5、 注册feign客户端；
1、registerFeignClients( )
public void registerFeignClients(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
LinkedHashSet<BeanDefinition> candidateComponents = new LinkedHashSet<>();
//1、获取 @EnableFeignClients 注解信息
Map<String, Object> attrs = metadata.getAnnotationAttributes(EnableFeignClients.class.getName());
//@FeignClient 注解类型过滤器
AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(FeignClient.class);
final Class<?>[] clients = attrs == null ? null : (Class<?>[]) attrs.get("clients");
//2、获取包含@FeignClient 注解的接口
if (clients == null || clients.length == 0) {
//注解中没有指定要加载的 FeignClient 接口类，则进行扫描指定的包或当前处理的配置类所在的包
//获取扫描器
ClassPathScanningCandidateComponentProvider scanner = getScanner();
scanner.setResourceLoader(this.resourceLoader);
//设置注解类型过滤器
scanner.addIncludeFilter(new AnnotationTypeFilter(FeignClient.class));
//获取@FeignClient注解上的value/basePackages/basePackageClasses 或当前处理的配置类所在的包
Set<String> basePackages = getBasePackages(metadata);
for (String basePackage : basePackages) {
//找出包含@FeignClient 注解的接口
candidateComponents.addAll(scanner.findCandidateComponents(basePackage));
}
}
else {
//注解中指定了要加载的 FeignClient 接口类
for (Class<?> clazz : clients) {
candidateComponents.add(new AnnotatedGenericBeanDefinition(clazz));
}
}
//3、解析@FeignClient接口
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<String, Object> attributes = annotationMetadata
.getAnnotationAttributes(FeignClient.class.getCanonicalName());
//@FeignClient制定的服务端的名称
String name = getClientName(attributes);
//根据服务端的名称注册FeignClientSpecification类
registerClientConfiguration(registry, name, attributes.get("configuration"));
//4、注册FeignClient
registerFeignClient(registry, annotationMetadata, attributes);
}
}
}
6、 注册FeignClient；
private void registerFeignClient(BeanDefinitionRegistry registry, AnnotationMetadata annotationMetadata,
Map<String, Object> attributes) {
String className = annotationMetadata.getClassName();
//设置类型为 FeignClientFactoryBean，实现了FactoryBean<Object>, InitializingBean, ApplicationContextAware接口
BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(FeignClientFactoryBean.class);
validate(attributes);
//获取注解属性，设置到beanDefinition中
definition.addPropertyValue("url", getUrl(attributes));
definition.addPropertyValue("path", getPath(attributes));
String name = getName(attributes);
definition.addPropertyValue("name", name);
String contextId = getContextId(attributes);
definition.addPropertyValue("contextId", contextId);
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 = contextId + "FeignClient";
AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
beanDefinition.setAttribute(FactoryBean.OBJECT_TYPE_ATTRIBUTE, className);
// has a default, won't be null
boolean primary = (Boolean) attributes.get("primary");
beanDefinition.setPrimary(primary);
String qualifier = getQualifier(attributes);
if (StringUtils.hasText(qualifier)) {
alias = qualifier;
}
BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className, new String[] {
alias });
//注册到spring容器
BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
}
三、实例化FeignClients
上一步中注册的 FeignClient 类型为 FeignClientFactoryBean 类型，FeignClientFactoryBean 实现了FactoryBean, InitializingBean, ApplicationContextAware接口，则在实例化过程中会调用 getObject( ) 和 afterPropertiesSet( ) 方法。
1、 afterPropertiesSet()；
只是做了一些校验
public void afterPropertiesSet() {
Assert.hasText(contextId, "Context id must be set");
Assert.hasText(name, "Name must be set");
}
2、 getObject()；
public Object getObject() {
return getTarget();
}
<T> T getTarget() {
//这里获取到feign的上下文信息，下面会对FeignContext做分析
FeignContext context = applicationContext.getBean(FeignContext.class);
//创建 Feign.Builder
Feign.Builder builder = feign(context);
if (!StringUtils.hasText(url)) {
//没有指定服务端的url，使用服务端的名称
if (!name.startsWith("http")) {
url = "http://" + name;
}
else {
url = name;
}
url += cleanPath();
//获取带有负载均衡的客户端
return (T) loadBalance(builder, context, new HardCodedTarget<>(type, name, url));
}
if (StringUtils.hasText(url) && !url.startsWith("http")) {
url = "http://" + url;
}
String url = this.url + cleanPath();
Client client = getOptional(context, Client.class);
if (client != null) {
if (client instanceof FeignBlockingLoadBalancerClient) {
// not load balancing because we have a url,
// but Spring Cloud LoadBalancer is on the classpath, so unwrap
client = ((FeignBlockingLoadBalancerClient) client).getDelegate();
}
builder.client(client);
}
Targeter targeter = get(context, Targeter.class);
return (T) targeter.target(this, builder, context, new HardCodedTarget<>(type, name, url));
}
3、 创建Feign.Builder；
1、feign( )
protected Feign.Builder feign(FeignContext context) {
FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
Logger logger = loggerFactory.create(type);
// @formatter:off
//根据FeignContext中的configuration，也就是@FeignClient中指定的configuration属性创建，没有指定configuration属性时，根据默认的一些配置创建，默认的配置定义在FeignClientsConfiguration配置类中
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
//配置Feign.Builder
configureFeign(context, builder);
//自定义的一些配置
applyBuildCustomizers(context, builder);
return builder;
}
2、configureFeign( )
protected void configureFeign(FeignContext context, Feign.Builder builder) {
//获取FeignClientProperties @ConfigurationProperties("feign.client")
FeignClientProperties properties = applicationContext.getBean(FeignClientProperties.class);
FeignClientConfigurer feignClientConfigurer = getOptional(context, FeignClientConfigurer.class);
setInheritParentContext(feignClientConfigurer.inheritParentConfiguration());
if (properties != null && inheritParentContext) {
if (properties.isDefaultToProperties()) {
//配置@FeignClient中指定的configuration属性：Logger.Level、Retryer、ErrorDecoder、FeignErrorDecoderFactory、Request.Options、RequestInterceptor、QueryMapEncoder、ExceptionPropagationPolicy
configureUsingConfiguration(context, builder);
//配置FeignClientProperties 中的默认属性
configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()), builder);
//配置FeignClientProperties 中指定的属性
configureUsingProperties(properties.getConfig().get(contextId), builder);
}
else {
configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()), builder);
configureUsingProperties(properties.getConfig().get(contextId), builder);
configureUsingConfiguration(context, builder);
}
}
else {
configureUsingConfiguration(context, builder);
}
}
3、applyBuildCustomizers( )
自定义配置回调 FeignBuilderCustomizer
private void applyBuildCustomizers(FeignContext context, Feign.Builder builder) {
Map<String, FeignBuilderCustomizer> customizerMap = context.getInstances(contextId,
FeignBuilderCustomizer.class);
if (customizerMap != null) {
customizerMap.values().stream().sorted(AnnotationAwareOrderComparator.INSTANCE)
.forEach(feignBuilderCustomizer -> feignBuilderCustomizer.customize(builder));
}
}
4、 loadBalance()；
protected <T> T loadBalance(Feign.Builder builder, FeignContext context, HardCodedTarget<T> target) {
//在DefaultFeignLoadBalancerConfiguration中默认创建FeignBlockingLoadBalancerClient
Client client = getOptional(context, Client.class);
if (client != null) {
//设置client
builder.client(client);
//默认是DefaultTargeter
Targeter targeter = get(context, Targeter.class);
//调用target()
return targeter.target(this, builder, context, target);
}
throw new IllegalStateException(
"No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-loadbalancer?");
}
5、 target()；
public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context,
Target.HardCodedTarget<T> target) {
return feign.target(target);
}
public <T> T target(Target<T> target) {
//创建feign 目标对象
return build().newInstance(target);
}
6、 build()；
增强feign里的属性，创建ReflectiveFeign
public Feign build() {
//通过自定义的Capability来增强各属性
Client client = Capability.enrich(this.client, capabilities);
Retryer retryer = Capability.enrich(this.retryer, capabilities);
List<RequestInterceptor> requestInterceptors = this.requestInterceptors.stream()
.map(ri -> Capability.enrich(ri, capabilities))
.collect(Collectors.toList());
Logger logger = Capability.enrich(this.logger, capabilities);
Contract contract = Capability.enrich(this.contract, capabilities);
Options options = Capability.enrich(this.options, capabilities);
Encoder encoder = Capability.enrich(this.encoder, capabilities);
Decoder decoder = Capability.enrich(this.decoder, capabilities);
InvocationHandlerFactory invocationHandlerFactory =
Capability.enrich(this.invocationHandlerFactory, capabilities);
QueryMapEncoder queryMapEncoder = Capability.enrich(this.queryMapEncoder, capabilities);
SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =
new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,
logLevel, decode404, closeAfterDecode, propagationPolicy, forceDecoding);
ParseHandlersByName handlersByName =
new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder,
errorDecoder, synchronousMethodHandlerFactory);
return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder);
}
}
7、 newInstance()；
public <T> T newInstance(Target<T> target) {
//方法名称与SynchronousMethodHandler的映射
Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
//方法与SynchronousMethodHandler的映射
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)));
}
}
//创建FeignInvocationHandler
InvocationHandler handler = factory.create(target, methodToHandler);
//创建代理对象
T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),
new Class<?>[] {
target.type()}, handler);
for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
//默认方法，使用句柄方法方式
defaultMethodHandler.bindTo(proxy);
}
return proxy;
}
最终创建出了@FeignClient接口的代理对象
四、FeignContext
FeignContext 作为feign的上下文，包含了 FeignClient中指定的一些配置信息
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(Feign.class)
@EnableConfigurationProperties({
FeignClientProperties.class, FeignHttpClientProperties.class })
@Import(DefaultGzipDecoderConfiguration.class)
public class FeignAutoConfiguration {
private static final Log LOG = LogFactory.getLog(FeignAutoConfiguration.class);
@Autowired(required = false)
private List<FeignClientSpecification> configurations = new ArrayList<>();
@Bean
public HasFeatures feignFeature() {
return HasFeatures.namedFeature("Feign", Feign.class);
}
//创建bean FeignContext
@Bean
public FeignContext feignContext() {
FeignContext context = new FeignContext();
//设置 FeignClientSpecification 类
context.setConfigurations(this.configurations);
return context;
}
...
}
FeignClientSpecification 类的注册在第二步中已经分析过。
总结
1、 给@FeignClient接口创建代理对象；
2、 创建增强handlerFeignInvocationHandler；
3、 创建SynchronousMethodHandler或DefaultMethodHandler处理真正的方法；