pom依赖
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
<version>2.2.3.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
<version>2.2.3.RELEASE</version>
</dependency>
案例
@FeignClient("spring-cloud-order-service")
public interface OrderServiceFeignClient {
@GetMapping("/orders")
String getAllOrder();
}
@RestController
public class OpenFeignController {
@Autowired
OrderServiceFeignClient orderServiceFeignClient;
@GetMapping("/test")
public String test(){
return orderServiceFeignClient.getAllOrder();
}
}
@EnableFeignClients
@SpringBootApplication
public class SpringCloudUserServiceApplication {
public static void main(String[] args) {
SpringApplication.run(SpringCloudUserServiceApplication.class, args);
}
}
服务端代码省略。
首先，阅读代码前应有对应的猜想，根据以往经验，我猜，加了@FeignClient的类，应该是生成了一个动态代理，注入到spring容器中，而这个动态代理，最终应该会使用对应的http客户端，如果有ribbon还会进行负载，默认，应该是restTemplate，带着猜想，接下来去阅读源码。
@EnableFeignClients
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(FeignClientsRegistrar.class)
public @interface EnableFeignClients {
/**
* Alias for the {@link #basePackages()} attribute. Allows for more concise annotation
* declarations e.g.: {@code @ComponentScan("org.my.pkg")} instead of
* {@code @ComponentScan(basePackages="org.my.pkg")}.
* @return the array of 'basePackages'.
*/
String[] value() default {};
/**
* Base packages to scan for annotated components.
* <p>
* {@link #value()} is an alias for (and mutually exclusive with) this attribute.
* <p>
* Use {@link #basePackageClasses()} for a type-safe alternative to String-based
* package names.
* @return the array of 'basePackages'.
*/
String[] basePackages() default {};
/**
* Type-safe alternative to {@link #basePackages()} for specifying the packages to
* scan for annotated components. The package of each class specified will be scanned.
* <p>
* Consider creating a special no-op marker class or interface in each package that
* serves no purpose other than being referenced by this attribute.
* @return the array of 'basePackageClasses'.
*/
Class<?>[] basePackageClasses() default {};
/**
* A custom <code>@Configuration</code> for all feign clients. Can contain override
* <code>@Bean</code> definition for the pieces that make up the client, for instance
* {@link feign.codec.Decoder}, {@link feign.codec.Encoder}, {@link feign.Contract}.
*
* @see FeignClientsConfiguration for the defaults
* @return list of default configurations
*/
Class<?>[] defaultConfiguration() default {};
/**
* List of classes annotated with @FeignClient. If not empty, disables classpath
* scanning.
* @return list of FeignClient classes
*/
Class<?>[] clients() default {};
}
关键注解FeignClientsRegistrar，实现ImportBeanDefinitionRegistrar，从而注册bean对象。
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
registerDefaultConfiguration(metadata, registry);//注册默认配置信息
registerFeignClients(metadata, registry);//注册feign客户端
}
public void registerFeignClients(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
ClassPathScanningCandidateComponentProvider scanner = getScanner();
scanner.setResourceLoader(this.resourceLoader);
Set<String> basePackages;
Map<String, Object> 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);//获取扫描包路径
}
else {
final Set<String> 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<BeanDefinition> candidateComponents = scanner
.findCandidateComponents(basePackage);//获取@FeignClient注解的bean
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());
String name = getClientName(attributes);
registerClientConfiguration(registry, name,
attributes.get("configuration"));//注册个性配置
registerFeignClient(registry, annotationMetadata, attributes);//注册FeignClient
}
}
}
}
registerFeignClient注册单个FeignClient
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);
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 });
BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
}
public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException {
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
String[] var4 = aliases;
int var5 = aliases.length;
for(int var6 = 0; var6 < var5; ++var6) {
String alias = var4[var6];
registry.registerAlias(beanName, alias);
}
}
}
上面逻辑主要是将FeignClientFactoryBean作为value，对应的@FeignClient注解的类名作为key，注册到spring容器中。
也就是说，业务逻辑中：
@Autowired
OrderServiceFeignClient orderServiceFeignClient;
实际注入的是FeignClientFactoryBean的工厂类的getObject返回的类。
FeignClientFactoryBean
public Object getObject() throws Exception {
return getTarget();
}
<T> T getTarget() {
FeignContext context = this.applicationContext.getBean(FeignContext.class);
Feign.Builder builder = feign(context);
if (!StringUtils.hasText(this.url)) {
if (!this.name.startsWith("http")) {
this.url = "http://" + this.name;
}
else {
this.url = this.name;
}
this.url += cleanPath();
return (T) loadBalance(builder, context,
new HardCodedTarget<>(this.type, this.name, this.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 load balancing because we have a url,
// but ribbon is on the classpath, so unwrap
client = ((LoadBalancerFeignClient) client).getDelegate();
}
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<>(this.type, this.name, url));
}
先获取FeignContext，在FeignAutoConfiguration有定义
@Bean
public FeignContext feignContext() {
FeignContext context = new FeignContext();
context.setConfigurations(this.configurations);
return context;
}
然后是builder，敲黑板，这个是重点哦，这个是重点哦，这个是重点哦。
protected Feign.Builder feign(FeignContext context) {
FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
Logger logger = loggerFactory.create(this.type);
// @formatter:off
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;
}
其中定义了，日志，编码，解码，通信协议等，后面会用到。
此时有两个分支，如果注解上写的是服务名，那么使用ribbon进行负载，否则就是http请求。此篇只看ribbon负载。
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?");
}
获取一个client客户端，并设置在builder中，这个客户端在FeignLoadBalancerAutoConfiguration中引入DefaultFeignLoadBalancedConfiguration
@Bean
@ConditionalOnMissingBean
public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
SpringClientFactory clientFactory) {
return new LoadBalancerFeignClient(new Client.Default(null, null), cachingFactory,
clientFactory);
}
返回一个LoadBalancerFeignClient，此时Target又是什么呢？
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(name = "feign.hystrix.HystrixFeign")
protected static class HystrixFeignTargeterConfiguration {
@Bean
@ConditionalOnMissingBean
public Targeter feignTargeter() {
return new HystrixTargeter();
}
}
@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingClass("feign.hystrix.HystrixFeign")
protected static class DefaultFeignTargeterConfiguration {
@Bean
@ConditionalOnMissingBean
public Targeter feignTargeter() {
return new DefaultTargeter();
}
}
如果有熔断组件hystrix，当然就返回HystrixTargeter，否则是DefaultTargeter。
class DefaultTargeter implements Targeter {
@Override
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) {
return this.build().newInstance(target);
}
public Feign build() {
Client client = (Client)Capability.enrich(this.client, this.capabilities);
Retryer retryer = (Retryer)Capability.enrich(this.retryer, this.capabilities);
List<RequestInterceptor> requestInterceptors = (List)this.requestInterceptors.stream().map((ri) -> {
return (RequestInterceptor)Capability.enrich(ri, this.capabilities);
}).collect(Collectors.toList());
Logger logger = (Logger)Capability.enrich(this.logger, this.capabilities);
Contract contract = (Contract)Capability.enrich(this.contract, this.capabilities);
Options options = (Options)Capability.enrich(this.options, this.capabilities);
Encoder encoder = (Encoder)Capability.enrich(this.encoder, this.capabilities);
Decoder decoder = (Decoder)Capability.enrich(this.decoder, this.capabilities);
InvocationHandlerFactory invocationHandlerFactory = (InvocationHandlerFactory)Capability.enrich(this.invocationHandlerFactory, this.capabilities);
QueryMapEncoder queryMapEncoder = (QueryMapEncoder)Capability.enrich(this.queryMapEncoder, this.capabilities);
Factory synchronousMethodHandlerFactory = new Factory(client, retryer, requestInterceptors, logger, this.logLevel, this.decode404, this.closeAfterDecode, this.propagationPolicy, this.forceDecoding);
ParseHandlersByName handlersByName = new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder, this.errorDecoder, synchronousMethodHandlerFactory);
return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder);
}
此时this.build返回ReflectiveFeign。
public <T> T newInstance(Target<T> target) {
Map<String, MethodHandler> nameToHandler = this.targetToHandlersByName.apply(target);
Map<Method, MethodHandler> methodToHandler = new LinkedHashMap();
List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList();
Method[] var5 = target.type().getMethods();
int var6 = var5.length;
for(int var7 = 0; var7 < var6; ++var7) {
Method method = var5[var7];
if (method.getDeclaringClass() != Object.class) {
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 = this.factory.create(target, methodToHandler);
T proxy = Proxy.newProxyInstance(target.type().getClassLoader(), new Class[]{target.type()}, handler);
Iterator var12 = defaultMethodHandlers.iterator();
while(var12.hasNext()) {
DefaultMethodHandler defaultMethodHandler = (DefaultMethodHandler)var12.next();
defaultMethodHandler.bindTo(proxy);
}
return proxy;
}
当当当当，终于看到jdk的动态代理，满眼泪光。
这里就是返回个动态对象，当对象被调用，实际先吊用InvocationHandler，那么InvocationHandler的初始化就显得非常重要了。
先看nameToHandler如何获得。
public Map<String, MethodHandler> apply(Target target) {
List<MethodMetadata> metadata = this.contract.parseAndValidateMetadata(target.type());
Map<String, MethodHandler> result = new LinkedHashMap();
Iterator var4 = metadata.iterator();
while(var4.hasNext()) {
MethodMetadata md = (MethodMetadata)var4.next();
Object buildTemplate;
if (!md.formParams().isEmpty() && md.template().bodyTemplate() == null) {
buildTemplate = new ReflectiveFeign.BuildFormEncodedTemplateFromArgs(md, this.encoder, this.queryMapEncoder, target);
} else if (md.bodyIndex() != null) {
buildTemplate = new ReflectiveFeign.BuildEncodedTemplateFromArgs(md, this.encoder, this.queryMapEncoder, target);
} else {
buildTemplate = new ReflectiveFeign.BuildTemplateByResolvingArgs(md, this.queryMapEncoder, target);
}
if (md.isIgnored()) {
result.put(md.configKey(), (args) -> {
throw new IllegalStateException(md.configKey() + " is not a method handled by feign");
});
} else {
result.put(md.configKey(), this.factory.create(target, md, (Factory)buildTemplate, this.options, this.decoder, this.errorDecoder));
}
}
return result;
}
首先明确contact是SpringMvcContract，这个在FeignClientsConfiguration中定义的。
@Bean
@ConditionalOnMissingBean
public Contract feignContract(ConversionService feignConversionService) {
return new SpringMvcContract(this.parameterProcessors, feignConversionService);
}
最后返回的metadata的格式为List<Map<String, MethodMetadata>>,map的key是对象名#方法名(参数类型),value是对象的元数据信息。
public MethodHandler create(Target<?> target, MethodMetadata md, feign.RequestTemplate.Factory buildTemplateFromArgs, Options options, Decoder decoder, ErrorDecoder errorDecoder) {
return new SynchronousMethodHandler(target, this.client, this.retryer, this.requestInterceptors, this.logger, this.logLevel, md, buildTemplateFromArgs, options, decoder, errorDecoder, this.decode404, this.closeAfterDecode, this.propagationPolicy, this.forceDecoding);
}
nameToHandler的value是SynchronousMethodHandler。
然后过滤nameToHandler生成一个代反射调用的methodToHandler设置到InvocationHandler中
public InvocationHandler create(Target target, Map<Method, InvocationHandlerFactory.MethodHandler> dispatch) {
return new FeignInvocationHandler(target, dispatch);
}
当代理对象执行时，执行invoke方法
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (!"equals".equals(method.getName())) {
if ("hashCode".equals(method.getName())) {
return this.hashCode();
} else {
return "toString".equals(method.getName()) ? this.toString() : ((MethodHandler)this.dispatch.get(method)).invoke(args);
}
} else {
try {
Object otherHandler = args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
return this.equals(otherHandler);
} catch (IllegalArgumentException var5) {
return false;
}
}
}
SynchronousMethodHandler
public Object invoke(Object[] argv) throws Throwable {
RequestTemplate template = this.buildTemplateFromArgs.create(argv);
Options options = this.findOptions(argv);
Retryer retryer = this.retryer.clone();
while(true) {
try {
return this.executeAndDecode(template, options);
} catch (RetryableException var9) {
RetryableException e = var9;
try {
retryer.continueOrPropagate(e);
} catch (RetryableException var8) {
Throwable cause = var8.getCause();
if (this.propagationPolicy == ExceptionPropagationPolicy.UNWRAP && cause != null) {
throw cause;
}
throw var8;
}
if (this.logLevel != Level.NONE) {
this.logger.logRetry(this.metadata.configKey(), this.logLevel);
}
}
}
}
开始构建RequestTemplate
public RequestTemplate create(Object[] argv) {
RequestTemplate mutable = RequestTemplate.from(this.metadata.template());
mutable.feignTarget(this.target);
if (this.metadata.urlIndex() != null) {
int urlIndex = this.metadata.urlIndex();
Util.checkArgument(argv[urlIndex] != null, "URI parameter %s was null", new Object[]{urlIndex});
mutable.target(String.valueOf(argv[urlIndex]));
}
Map<String, Object> varBuilder = new LinkedHashMap();
Iterator var4 = this.metadata.indexToName().entrySet().iterator();
while(true) {
Entry entry;
int i;
Object value;
do {
if (!var4.hasNext()) {
RequestTemplate template = this.resolve(argv, mutable, varBuilder);
if (this.metadata.queryMapIndex() != null) {
Object value = argv[this.metadata.queryMapIndex()];
Map<String, Object> queryMap = this.toQueryMap(value);
template = this.addQueryMapQueryParameters(queryMap, template);
}
if (this.metadata.headerMapIndex() != null) {
template = this.addHeaderMapHeaders((Map)argv[this.metadata.headerMapIndex()], template);
}
return template;
}
entry = (Entry)var4.next();
i = (Integer)entry.getKey();
value = argv[(Integer)entry.getKey()];
} while(value == null);
if (this.indexToExpander.containsKey(i)) {
value = this.expandElements((Expander)this.indexToExpander.get(i), value);
}
Iterator var8 = ((Collection)entry.getValue()).iterator();
while(var8.hasNext()) {
String name = (String)var8.next();
varBuilder.put(name, value);
}
}
}
protected RequestTemplate resolve(Object[] argv, RequestTemplate mutable, Map<String, Object> variables) {
Map<String, Object> formVariables = new LinkedHashMap();
Iterator var5 = variables.entrySet().iterator();
while(var5.hasNext()) {
Entry<String, Object> entry = (Entry)var5.next();
if (this.metadata.formParams().contains(entry.getKey())) {
formVariables.put(entry.getKey(), entry.getValue());
}
}
try {
this.encoder.encode(formVariables, Encoder.MAP_STRING_WILDCARD, mutable);
} catch (EncodeException var7) {
throw var7;
} catch (RuntimeException var8) {
throw new EncodeException(var8.getMessage(), var8);
}
return super.resolve(argv, mutable, variables);
}
resolve时，对请求参数进行了编码
Object executeAndDecode(RequestTemplate template, Options options) throws Throwable {
Request request = this.targetRequest(template);
if (this.logLevel != Level.NONE) {
this.logger.logRequest(this.metadata.configKey(), this.logLevel, request);
}
long start = System.nanoTime();
Response response;
try {
response = this.client.execute(request, options);
response = response.toBuilder().request(request).requestTemplate(template).build();
} catch (IOException var13) {
if (this.logLevel != Level.NONE) {
this.logger.logIOException(this.metadata.configKey(), this.logLevel, var13, this.elapsedTime(start));
}
throw FeignException.errorExecuting(request, var13);
}
long elapsedTime = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);
if (this.decoder != null) {
return this.decoder.decode(response, this.metadata.returnType());
} else {
CompletableFuture<Object> resultFuture = new CompletableFuture();
this.asyncResponseHandler.handleResponse(resultFuture, this.metadata.configKey(), response, this.metadata.returnType(), elapsedTime);
try {
if (!resultFuture.isDone()) {
throw new IllegalStateException("Response handling not done");
} else {
return resultFuture.join();
}
} catch (CompletionException var12) {
Throwable cause = var12.getCause();
if (cause != null) {
throw cause;
} else {
throw var12;
}
}
}
}
此时使用LoadBalancerFeignClient发起请求，请求返回后，进行response解码
到此，后面内容不在分析，无非是loadbalancer解析地址，发送http请求访问而已
