Spring Cloud专题之二:OpenFeign 远程调用服务
欢迎查看上一篇博客:SpringCloud专题之一:Eureka 。
OpenFeign是一种声明式的webservice客户端调用框架。你只需要声明接口和一些简单的注解,就能像使用普通的Bean一样调用远程服务,Ribbon 和 OpenFeign 都可以实现服务调用和实现负载均衡.OpenFeign 也内置了Ribbon.
OpenFeign是在feign的基础上做了一些修改封装,增加了对Spring Mvc注解的支持.
OpenFiegn注解讲解
一般我们会使用@GetMapping和@PostMapping两种方式来调用Rest服务。
使用@RequestParam和@RequestBody来获取参数
@RequestBody只能用在Post请求中,并且一个Post请求只能有一个@RequestBody,@RequestBody的参数可以包含复杂类型。
@RequestParam可以用在Post和Get请求中,但是要注意,@RequestParam的参数只能是基本类型或者是Enum,或者是List和Map(List和Map里只能是基本类型),所以@RequestParam可以和@RequestBody一起使用。
如果是Get请求,但是有时复合类型怎么办呢?比如我们想传递一个User对象,User对象里面只有普通的两个String属性,就可以使用@SpringQueryMap。@SpringQueryMap的参数是鞥你是普通的POJO,不能是复合类型,否则解析不了,如果必须使用复合类型,那么使用@RequestBody吧。
多个FeignClient使用同一个name的问题
在eureka的客户端添加一个类:
/**
* @className: Hello1Controller
* @description: 测试多个feign使用相同的name的问题
* @author: charon
* @create: 2021-06-06 09:35
*/
@RestController
public class Hello1Controller {
/**
* 日志记录类
*/
private final Logger logger = LoggerFactory.getLogger(getClass());
@Value("${server.port}")
private String host;
@Value("${spring.application.name}")
private String instanceName;
@RequestMapping("/sayHello1")
public String sayHello1(@RequestParam("name") String name){
logger.info("你好,服务名:{},端口为:{},接收到的参数为:{}",instanceName,host,name);
return "你好,服务名:"+instanceName+",端口为:"+host+",接收到的参数为:"+name;
}
}
eureka消费者端的controller里添加sayHello1(String name)方法:
/**
* @className: CustomerController
* @description:
* @author: charon
* @create: 2021-05-19 22:56
*/
@RestController
public class CustomerController {
@Autowired
private CustomerSerivce serivce;
@RequestMapping("/sayHello")
public String invokeSayHello(){
return serivce.invokeSayHello();
}
@RequestMapping("/sayHello1")
public String invokeSayHello1(String name){
return serivce.invokeSayHello1(name);
}
}
接口及实现类:
/**
* @className: CustomerSerivce
* @description:
* @author: charon
* @create: 2021-05-19 22:56
*/
public interface CustomerSerivce {
String invokeSayHello();
String invokeSayHello1(String name);
}
@Service
public class CustomerServiceImpl implements CustomerSerivce {
@Autowired
private CustomerFeign feign;
@Autowired
private Customer1Feign feign1;
@Override
public String invokeSayHello() {
return feign.sayHello();
}
@Override
public String invokeSayHello1(String name) {
return feign1.sayHello1(name);
}
}
feignClient:
/**
* @className: CustomerFeign
* @description: @FeignClient使用的value参数,表示从HELLO-SERVER这个服务中调用服务
* @author: charon
* @create: 2021-05-19 23:01
*/
@FeignClient("HELLO-SERVER")
public interface CustomerFeign {
/**
* 要求:
* 返回值要对应,方法名随意,参数值要对应
* 方法上添加SpringMVC的注解
* @return
*/
@RequestMapping("/sayHello")
String sayHello();
}
/**
* @className: Customer1Feign
* @description: 测试多个feign使用相同的name的问题
* @author: charon
* @create: 2021-06-06 09:42
*/
@FeignClient("HELLO-SERVER")
public interface Customer1Feign {
/**
* 要求:
* 必须要指定RequestParam属性的value值,同时RequestMethod的method也需要指定
* 方法上添加SpringMVC的注解
* @return
*/
@RequestMapping(value = "/sayHello1",method = RequestMethod.GET)
String sayHello1(@RequestParam("name") String name);
}
如上图所示,运行时候就会报错。 原因是两个FeignClient使用了同一个value,对于同一个service-id
只能使用一个配置类,如果有多个@FeignClient
注解使用了相同的name
属性,则注解的configuration
参数会被覆盖。至于谁覆盖谁要看Spring容器初始化Bean的顺序。
改动:
# 设置为true,表示后发现的bean会覆盖之前相同名称的bean
spring.main.allow-bean-definition-overriding=true
源码解读
openfeign的自动配置
@EnableFeignClients开启openfeign
首先,我们从@EnableFeignClients这个注解开始了解。
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(FeignClientsRegistrar.class)
public @interface EnableFeignClients {
}
这个注解导入了一个类FeignClientsRegistrar,这个类实现了ImportBeanDefinitionRegistrar接口,该接口用于向Bean容器中注册添加BeanDefinition。
跟进FeignClientsRegistrar的registerBeanDefinitions方法,看看它注册了哪些东西。
public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
// 注册默认配置,会读取@EnableFeignClients接口的属性,如果存在自定义配置类那么就会被注册到容器中
registerDefaultConfiguration(metadata, registry);
// 注册FeignClient接口的Bean,会扫描所有注解了@FeignClient的接口,然后像spring本地Bean一样地注册到容器中。
registerFeignClients(metadata, registry);
}
下面重点看看,registerFeignClients方法,这个方法的核心逻辑就是扫描类路径,获取BeanDefinition,然后遍历进行注册。
public void registerFeignClients(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
LinkedHashSet<BeanDefinition> candidateComponents = new LinkedHashSet<>();
Map<String, Object> attrs = metadata
.getAnnotationAttributes(EnableFeignClients.class.getName());
final Class<?>[] clients = attrs == null ? null
: (Class<?>[]) attrs.get("clients");
if (clients == null || clients.length == 0) {
ClassPathScanningCandidateComponentProvider scanner = getScanner();
scanner.setResourceLoader(this.resourceLoader);
scanner.addIncludeFilter(new AnnotationTypeFilter(FeignClient.class));
// 扫描所有路径,默认情况下扫描启动类下的路径
Set<String> basePackages = getBasePackages(metadata);
for (String basePackage : basePackages) {
// 将所有 @FeignClient 的接口的BeanDefinition拿到
candidateComponents.addAll(scanner.findCandidateComponents(basePackage));
}
}
else {
for (Class<?> clazz : clients) {
candidateComponents.add(new AnnotatedGenericBeanDefinition(clazz));
}
}
// 遍历扫描到的FeignClient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);
// 注册FeignClient的配置
registerClientConfiguration(registry, name,attributes.get("configuration"));
// 注册FeignClient
registerFeignClient(registry, annotationMetadata, attributes);
}
}
}
下面来看看注册FeignClient的方法:
private void registerFeignClient(BeanDefinitionRegistry registry,
AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
String className = annotationMetadata.getClassName();
Class clazz = ClassUtils.resolveClassName(className, null);
ConfigurableBeanFactory beanFactory = registry instanceof ConfigurableBeanFactory
? (ConfigurableBeanFactory) registry : null;
String contextId = getContextId(beanFactory, attributes);
String name = getName(attributes);
FeignClientFactoryBean factoryBean = new FeignClientFactoryBean();
factoryBean.setBeanFactory(beanFactory);
factoryBean.setName(name);
factoryBean.setContextId(contextId);
factoryBean.setType(clazz);
// 使用FactoryBean,将Bean的具体生成过程收拢到FeignClientFactoryBean之中
BeanDefinitionBuilder definition = BeanDefinitionBuilder
.genericBeanDefinition(clazz, () -> {
factoryBean.setUrl(getUrl(beanFactory, attributes));
factoryBean.setPath(getPath(beanFactory, attributes));
factoryBean.setDecode404(Boolean
.parseBoolean(String.valueOf(attributes.get("decode404"))));
Object fallback = attributes.get("fallback");
if (fallback != null) {
factoryBean.setFallback(fallback instanceof Class
? (Class<?>) fallback
: ClassUtils.resolveClassName(fallback.toString(), null));
}
Object fallbackFactory = attributes.get("fallbackFactory");
if (fallbackFactory != null) {
factoryBean.setFallbackFactory(fallbackFactory instanceof Class
? (Class<?>) fallbackFactory
: ClassUtils.resolveClassName(fallbackFactory.toString(),
null));
}
return factoryBean.getObject();
});
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
definition.setLazyInit(true);
validate(attributes);
AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
beanDefinition.setAttribute(FactoryBean.OBJECT_TYPE_ATTRIBUTE, className);
beanDefinition.setAttribute("feignClientsRegistrarFactoryBean", factoryBean);
// has a default, won't be null
boolean primary = (Boolean) attributes.get("primary");
beanDefinition.setPrimary(primary);
String[] qualifiers = getQualifiers(attributes);
if (ObjectUtils.isEmpty(qualifiers)) {
qualifiers = new String[] { contextId + "FeignClient" };
}
BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className, qualifiers);
// 将这个使用了 @FeignClient 的接口的工厂Bean的 BeanDefinition 注册到Spring容器中
BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
}
这里值得注意的是genericBeanDefinition方法最终生成的其实是FeignClientFactoryBean,而registerBeanDefinition方法注册进容器的也是FeignClientFactoryBean。而FeignClientFactoryBean是FactoryBean的实现类。FactoryBean接口是spring开放出来的,用于自定义Bean的生成过程。也就是说,spring将会通过调用FeignClientFactoryBean的getObject来获取@FeignClient注解的接口对应的Bean对象。
openfeign生成并调用客户端动态代理对象
从FeignClientFactoryBean的getObject()方法开始,看看代理对象的生成。getObject()方法调用了一个getTarget()方法,该方法做了一些预处理。获取了一个上下文以及Feign的构造器,没有URL的情况下拼接了一个。
@Override
public Object getObject() {
return getTarget();
}
<T> T getTarget() {
// 获取上下文,FeignContext是在FeignAutoConfiguration被解析的时候成为Bean.
FeignContext context = beanFactory != null ? beanFactory.getBean(FeignContext.class)
: applicationContext.getBean(FeignContext.class);
// feign用于构建代理对象,builder将会构建feign
Feign.Builder builder = feign(context);
if (!StringUtils.hasText(url)) {
// 然后在没有url 的情况下是按照服务名进行处理,拼接url 属性为http://服务名称。
// 如果有URL会按照URL的方式进行处理,并且如果URL没有加http:// 会在这里加上,也就是URL可以只写域名加端口
if (!name.startsWith("http")) {
url = "http://" + name;
}
else {
url = name;
}
url += cleanPath();
// HardCodedTarget 对象,实际上就是一个记录的功能,记录了接口类型,服务名称,地址信息
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 LoadBalancerFeignClient) {
client = ((LoadBalancerFeignClient) client).getDelegate();
}
if (client instanceof FeignBlockingLoadBalancerClient) {
client = ((FeignBlockingLoadBalancerClient) client).getDelegate();
}
if (client instanceof RetryableFeignBlockingLoadBalancerClient) {
client = ((RetryableFeignBlockingLoadBalancerClient) client)
.getDelegate();
}
builder.client(client);
}
Targeter targeter = get(context, Targeter.class);
return (T) targeter.target(this, builder, context,
new HardCodedTarget<>(type, name, url));
}
用org.springframework.cloud.openfeign.FeignClientFactoryBean#loadBalance 方法:
protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
HardCodedTarget<T> target) {
// 获取执行HTTP请求的client对象
Client client = getOptional(context, Client.class);
if (client != null) {
builder.client(client);
// 获取Target对象,默认为HystrixTargeter
Targeter targeter = get(context, Targeter.class);
// 创建代理对象
return targeter.target(this, builder, context, target);
}
}
跟进HystrixTargeter的target方法:
@Override
public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
FeignContext context, Target.HardCodedTarget<T> target) {
if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) {
return feign.target(target);
}
feign.hystrix.HystrixFeign.Builder builder = (feign.hystrix.HystrixFeign.Builder) feign;
String name = StringUtils.isEmpty(factory.getContextId()) ? factory.getName()
: factory.getContextId();
SetterFactory setterFactory = getOptional(name, context, SetterFactory.class);
if (setterFactory != null) {
builder.setterFactory(setterFactory);
}
Class<?> fallback = factory.getFallback();
if (fallback != void.class) {
return targetWithFallback(name, context, target, builder, fallback);
}
Class<?> fallbackFactory = factory.getFallbackFactory();
if (fallbackFactory != void.class) {
return targetWithFallbackFactory(name, context, target, builder,
fallbackFactory);
}
return feign.target(target);
}
HystrixTargeter的target方法里,最后调用了feign.target(target);方法,feign实现了构造代理对象的过程,所以这里将会回调feign的构造过程方法,在feign的target方法中,将会构造出一个Feign对象,并返回对象。
public <T> T target(Target<T> target) {
return build().newInstance(target);
}
public Feign build() {
// ...
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);
}
跟进ReflectiveFeign#newInstance方法,主要是通过JDK的动态代理构建代理对象:
public <T> T newInstance(Target<T> target) {
Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
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)));
}
}
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;
}
代理对象的构建主要由3个内容组成:
- 构建Method到MethodHandler的映射关系,后面调用代理对象的时候将会根据Method找到MethodHandler,然后调用MethodHandler的invoke方法,而MethodHandler包含发起HTTP请求的实现。
- jdk动态代理需要提供InvocationHandler。而InvocationHandler将由InvocationHandlerFactory的create方法实现。
- 通过Proxy.newProxyInstance方法,生成proxy对象。
调用proxy对象发起HTTP请求
我们都知道,JDK的动态代理将会调用FeignInvocationHandler(ReflectiveFeign的静态内部类)的invoke方法.
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// equals、toString、hashcode方法特殊处理
return dispatch.get(method).invoke(args);
}
在前面构建代理对象的时候,构建了Method到MethodHandler的映射关系.所以在这里就是根据method来获取到MethodHandler,在调用invoke方法的.
进入到invoke方法里,MethodHandler接口的默认实现类为SynchronousMethodHandler:
@Override
public Object invoke(Object[] argv) throws Throwable {
// 根据上面创建对象过程中解析出来的RequestTemplate克隆一个RequestTemplate
RequestTemplate template = buildTemplateFromArgs.create(argv);
Options options = findOptions(argv);
Retryer retryer = this.retryer.clone();
while (true) {
try {
// executeAndDecode将会负责发起http请求
return executeAndDecode(template, options);
} catch (RetryableException e) {
try {
retryer.continueOrPropagate(e);
} catch (RetryableException th) {
// ...
}
continue;
}
}
}
Object executeAndDecode(RequestTemplate template, Options options) throws Throwable {
// 对FeignInteceptor 拦截器做处理,并将信息封装到feign.Request 类中
Request request = targetRequest(template);
if (logLevel != Logger.Level.NONE) {
logger.logRequest(metadata.configKey(), logLevel, request);
}
Response response;
long start = System.nanoTime();
try {
// 执行HTTP请求
response = client.execute(request, options);
// ensure the request is set. TODO: remove in Feign 12
response = response.toBuilder()
.request(request)
.requestTemplate(template)
.build();
} 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);
// 解码结果
if (decoder != null)
return decoder.decode(response, metadata.returnType());
CompletableFuture<Object> resultFuture = new CompletableFuture<>();
asyncResponseHandler.handleResponse(resultFuture, metadata.configKey(), response,
metadata.returnType(),
elapsedTime);
try {
if (!resultFuture.isDone())
throw new IllegalStateException("Response handling not done");
return resultFuture.join();
} catch (CompletionException e) {
Throwable cause = e.getCause();
if (cause != null)
throw cause;
throw e;
}
}
总结
openFeign生成@FeignClient注解的接口的代理对象是从FeignClientFactoryBean的getObject方法开始的,生成proxy对象主要由ReflectiveFeign对象来实现。动态代理方法由jdk原生的动态代理支持。
调用proxy对象,其实就是发起http请求,请求结果将被解码并返回。
所以,正如Feign本身的意义一样,http远程调用被伪装成了本地调用一样简单的代理对象,对于使用者来说就是调用本地接口一样简单
参考文章:
https://zhuanlan.zhihu.com/p/133378040