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:

  1. 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。
  2. jdk动态代理需要提供InvocationHandler。而InvocationHandler将由InvocationHandlerFactory的create方法实现。
  3. 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

https://blog.csdn.net/manzhizhen/article/details/110013311

https://www.cnblogs.com/qlqwjy/p/14568086.html

本文版权归Charon和博客园共有,原创文章,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文连接,否则保留追究法律责任的权利。
posted @ 2021-06-13 22:56  pluto_charon  阅读(163)  评论(0编辑  收藏  举报