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【一起学源码-微服务】Feign 源码二：Feign动态代理构造过程

一枝花算不算浪漫 人气:1

前言

前情回顾

上一讲主要看了@EnableFeignClients中的registerBeanDefinitions()方法，这里面主要是
将EnableFeignClients注解对应的配置属性注入，将FeignClient注解对应的属性注入。

最后是生成FeignClient对应的bean，注入到Spring 的IOC容器。

本讲目录

目录如下：

  1. registerFeignClient()回顾
  2. FeignClientFactoryBean.getObject()解析
  3. Feign.builder()及client()构建逻辑
  4. 创建Feign动态代理实现细节

说明

原创不易，如若转载 请标明来源！

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源码分析

registerFeignClient()回顾

回顾下之前的代码：

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);
    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 = name + "FeignClient";
    AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();

    boolean primary = (Boolean)attributes.get("primary"); // has a default, won't be null

    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);
}

在registerFeignClient()方法中构造了一个BeanDefinitionBuilder对象，BeanDefinitionBuilder的主要作用就是构建一个AbstractBeanDefinition，AbstractBeanDefinition类最终被构建成一个BeanDefinitionHolder 然后注册到Spring中。

beanDefinition类为FeignClientFactoryBean，故在Spring获取类的时候实际返回的是FeignClientFactoryBean类。

FeignClientFactoryBean作为一个实现了FactoryBean的工厂类，那么每次在Spring Context 创建实体类的时候会调用它的getObject()方法。

FeignClientFactoryBean.getObject()解析

这里直接分析FeignClientFactoryBean.getObject()方法，这里包含着Feign动态代理的原理。

先看下代码：

@Override
public Object getObject() throws Exception {
    // 可以类比于ribbon中的SpringClientFactory，每个服务都对应一个独立的spring容器
    FeignContext context = applicationContext.getBean(FeignContext.class);
    // builder中包含contract、logLevel、encoder、decoder、options等信息
    Feign.Builder builder = feign(context);

    // 如果@FeignClient注解上没有指定url，说明是要用ribbon的负载均衡
    if (!StringUtils.hasText(this.url)) {
        String url;
        if (!this.name.startsWith("http")) {
            url = "http://" + this.name;
        }
        else {
            url = this.name;
        }
        // 这里构建的url类似于：http://serviceA
        url += cleanPath();
        return loadBalance(builder, context, new HardCodedTarget<>(this.type,
                this.name, 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 lod balancing because we have a url,
            // but ribbon is on the classpath, so unwrap
            client = ((LoadBalancerFeignClient)client).getDelegate();
        }
        builder.client(client);
    }
    Targeter targeter = get(context, Targeter.class);
    return targeter.target(this, builder, context, new HardCodedTarget<>(
            this.type, this.name, url));
}

public <T> T getInstance(String name, Class<T> type) {
    // getContext是从SpringClientContext中获取，之前讲ribbon源码时讲过
    // 一个serviceName都会有自己的一个SpringClientContext上下文信息
    AnnotationConfigApplicationContext context = getContext(name);
    if (BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context,
            type).length > 0) {
        // 这里是获取到LoadBalancerFeignClient
        return context.getBean(type);
    }
    return null;
}

首先是FeignContext ，我们可以类比下ribbon中的SpringClientFactory, 每个服务的调用，都有一个独立的ILoadBalancer、IRule、IPing等等，每个服务都对应一个独立的spring容器，从那个独立的容器中，可以取出这个服务关联的属于自己的LoadBalancer之类的东西。

如果我们调用一个服务的话，比如ServiceA，那么这个服务就会关联一个spring容器，FeignContext就代表一个独立的容器，关联着自己独立的一些组件，例如Logger组件、Decoder组件、Encoder组件等等。

我们可以看下FeignAutoConfiguration中：

@Configuration
@ConditionalOnClass(Feign.class)
@EnableConfigurationProperties({FeignClientProperties.class, FeignHttpClientProperties.class})
public class FeignAutoConfiguration {
    @Bean
    public FeignContext feignContext() {
        FeignContext context = new FeignContext();
        // configurations是一个Map结构
        context.setConfigurations(this.configurations);
        return context;
    }
}

public class FeignContext extends NamedContextFactory<FeignClientSpecification> {

    public FeignContext() {
        // FeignClientsConfiguration中会加载Encoder、Decoder、Logger等组件
        super(FeignClientsConfiguration.class, "feign", "feign.client.name");
    }
}

这里可以知道FeignContext的结构，里面其实就是封装了一个服务实例（ServiceA）对应的各种组件，其中FeignClientsConfiguration是加载默认的组件信息配置类。

接下来还是回到FeignClientFactoryBean.getObject()中，接着看feign()方法：

protected Feign.Builder feign(FeignContext context) {
    // 从context中获取到默认Logger组件：Slf4jLogger
    FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
    Logger logger = loggerFactory.create(this.type);

    // 从context中找type：Feign.Builder.class 对应的组件信息
    // 然后往builder中放入各种组件信息
    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;
}

protected <T> T get(FeignContext context, Class<T> type) {
    // context中转载的有Logger组件信息，这里默认的是Slf4jLogger
    T instance = context.getInstance(this.name, type);
    if (instance == null) {
        throw new IllegalStateException("No bean found of type " + type + " for "
                + this.name);
    }
    return instance;
}

这里是构造一个Feign.builder()对象，里面还是封装了各种组件信息。其中Feign.builder在FeignClientsConfiguration被初始化，一般使用的是HystrixFeign.builder()

@Configuration
public class FeignClientsConfiguration {
    // 一般环境都会配置feign.hystrix.enabled = true，这里直接看HystrixFeign.builder();
    @Configuration
    @ConditionalOnClass({ HystrixCommand.class, HystrixFeign.class })
    protected static class HystrixFeignConfiguration {
        @Bean
        @Scope("prototype")
        @ConditionalOnMissingBean
        @ConditionalOnProperty(name = "feign.hystrix.enabled", matchIfMissing = false)
        public Feign.Builder feignHystrixBuilder() {
            return HystrixFeign.builder();
        }
    }
}

接着看configureFeign() 方法，这个方法是读取application.properties中的配置信息。这里有个很有趣的配置：

configureUsingProperties(properties.getConfig().get(properties.getDefaultConfig()), builder);
configureUsingProperties(properties.getConfig().get(this.name), builder);

如果我们配置feign，先指定一个全局配置，在指定针对于某个服务的配置，那么某个服务配置的优先级会覆盖全局的配置。

一张图总结下Feign.builder()构建的过程：

Feign.builder()及client()构建逻辑

还是接着上面getObject() 方法去分析，上面分析完了Feign.builder()的构建，下面接着看看剩下的代码。

loadBalance(builder, context, new HardCodedTarget<>(this.type,this.name, url));

这里形式构造了一个HardCodeTarget对象，这个对象包含了接口类型（com.barrywang.service.feign.ServiceAFeignClient）、服务名称（ServiceA）、url地址（http://ServiceA），跟Feign.Builder、FeignContext，一起，传入了loadBalance()方法里去。

接着查看loadBalance() 方法：

protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
            HardCodedTarget<T> target) {
    // 这里还是从context中获取feignClient数据
    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?");
}

protected <T> T getOptional(FeignContext context, Class<T> type) {
    return context.getInstance(this.name, type);
}

这里还是从context中获取Client.class对应的数据，我们继续查看FeignAutoConfiguration 类，但是并没有发现Feign.client相关的数据，查看FeignAutoConfiguration的依赖，可以找到FeignRibbonClientAutoConfiguration ，代码如下：

@ConditionalOnClass({ ILoadBalancer.class, Feign.class })
@Configuration
@AutoConfigureBefore(FeignAutoConfiguration.class)
@EnableConfigurationProperties({ FeignHttpClientProperties.class })
// 这里会import三个FeignLoadBalance配置
@Import({ HttpClientFeignLoadBalancedConfiguration.class,
        OkHttpFeignLoadBalancedConfiguration.class,
        DefaultFeignLoadBalancedConfiguration.class })
public class FeignRibbonClientAutoConfiguration {

    @Bean
    @Primary
    @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
    public CachingSpringLoadBalancerFactory cachingLBClientFactory(
            SpringClientFactory factory) {
        return new CachingSpringLoadBalancerFactory(factory);
    }

    @Bean
    @Primary
    @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
    public CachingSpringLoadBalancerFactory retryabeCachingLBClientFactory(
        SpringClientFactory factory,
        LoadBalancedRetryPolicyFactory retryPolicyFactory,
        LoadBalancedBackOffPolicyFactory loadBalancedBackOffPolicyFactory,
        LoadBalancedRetryListenerFactory loadBalancedRetryListenerFactory) {
        return new CachingSpringLoadBalancerFactory(factory, retryPolicyFactory, loadBalancedBackOffPolicyFactory, loadBalancedRetryListenerFactory);
    }

    // Options是超时相关的配置
    @Bean
    @ConditionalOnMissingBean
    public Request.Options feignRequestOptions() {
        return LoadBalancerFeignClient.DEFAULT_OPTIONS;
    }
}

@Configuration
class DefaultFeignLoadBalancedConfiguration {
    @Bean
    @ConditionalOnMissingBean
    public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
                              SpringClientFactory clientFactory) {
        return new LoadBalancerFeignClient(new Client.Default(null, null),
                cachingFactory, clientFactory);
    }
}

到了这里就知道了，这里Feign.client默认应该就是LoadBalancerFeignClient了。

到这继续用一张图总结下：

创建Feign动态代理实现细节

接着上面代码，默认Feign.client()为LoadBalancerFeignClient, 然后将client加入到builder中。接着继续跟进targer相关：

protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
        HardCodedTarget<T> target) {
    Client client = getOptional(context, Client.class);
    if (client != null) {
        builder.client(client);
        // 这里又是通过Targer然后再context中获取默认配置
        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?");
}

protected <T> T get(FeignContext context, Class<T> type) {
    T instance = context.getInstance(this.name, type);
    if (instance == null) {
        throw new IllegalStateException("No bean found of type " + type + " for "
                + this.name);
    }
    return instance;
}

可以看到，这里又是通过Targeter.class从context中获取对应默认Targter。我们继续通过FeignAutoConfiguration中进行查找：

@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;
    }

    // 如果配置了feign.hystrix.HystrixFeign 则创建HystrixTargeter
    @Configuration
    @ConditionalOnClass(name = "feign.hystrix.HystrixFeign")
    protected static class HystrixFeignTargeterConfiguration {
        @Bean
        @ConditionalOnMissingBean
        public Targeter feignTargeter() {
            return new HystrixTargeter();
        }
    }

    // 如果没有配置feign.hystrix.HystrixFeign 则创建DefaultTargeter
    @Configuration
    @ConditionalOnMissingClass("feign.hystrix.HystrixFeign")
    protected static class DefaultFeignTargeterConfiguration {
        @Bean
        @ConditionalOnMissingBean
        public Targeter feignTargeter() {
            return new DefaultTargeter();
        }
    }
}

在默认情况下，feign是和hystrix整合的，feign.hystrix.HystrixFeign会有配置，所以这里默认Targeter使用的是HystrixTargeter, 在loadBalance()方法中执行的targeter.target()方法就是执行HystrixTargeter.target()方法：

class HystrixTargeter implements Targeter {
    public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context,
                        Target.HardCodedTarget<T> target) {
    // 判断Feign.builder()类型
    if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) {
        return feign.target(target);
    }
    feign.hystrix.HystrixFeign.Builder builder = (feign.hystrix.HystrixFeign.Builder) feign;
    SetterFactory setterFactory = getOptional(factory.getName(), context,
        SetterFactory.class);
    if (setterFactory != null) {
        builder.setterFactory(setterFactory);
    }
    Class<?> fallback = factory.getFallback();
    if (fallback != void.class) {
        return targetWithFallback(factory.getName(), context, target, builder, fallback);
    }
    Class<?> fallbackFactory = factory.getFallbackFactory();
    if (fallbackFactory != void.class) {
        return targetWithFallbackFactory(factory.getName(), context, target, builder, fallbackFactory);
    }

    // 最终都会执行feign.target()方法
    return feign.target(target);
}


public abstract class Feign {

  public static Builder builder() {
    return new Builder();
  }

  /**
   * Returns a new instance of an HTTP API, defined by annotations in the {@link Feign Contract},
   * for the specified {@code target}. You should cache this result.
   */
  public abstract <T> T newInstance(Target<T> target);

  public static class Builder {

    // 省略部分代码


    public <T> T target(Target<T> target) {
      return build().newInstance(target);
    }

    public Feign build() {
      // 构建一个SynchronousMethodHandler工厂
      SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =
          new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,
                                               logLevel, decode404);

      // 构建
      ParseHandlersByName handlersByName =
          new ParseHandlersByName(contract, options, encoder, decoder,
                                  errorDecoder, synchronousMethodHandlerFactory);
      return new ReflectiveFeign(handlersByName, invocationHandlerFactory);
    }
  }
}

这里主要是build方法，构造了一个ReflectieFein对象，接着看它里面的newInstance()方法：

@Override
public <T> T newInstance(Target<T> target) {
    // nameToHandler是@FeignClient中的方法名对应的MethodHandler对象
    Map<String, InvocationHandlerFactory.MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
    Map<Method, InvocationHandlerFactory.MethodHandler> methodToHandler = new LinkedHashMap<Method, InvocationHandlerFactory.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 {
            // 将具体的method作为map的key值
            methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
        }
    }

    // JDK动态代理 返回类似于：ReflectiveFeign$FeignInvocationHandler@7642
    // methodToHandler中包含Feign.builder()、Feign.client()等信息
    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;
}

这里就是使用了JDK动态代理，实际上返回的Feign动态代理的对象类似于：ReflectiveFeign$FeignInvocationHandler@7642。

这也和我们第一讲中的debug截图一致了，到了这里feign动态代理对象的生成原理都已经很清楚了。

最后debug一下，看下最终生成的动态代理对象：

总结

最后用一张图总结Feign动态代理生成的规则：

  1. 生成Feign.builder(),里面包含Encoder、Decoder、Logger等组件，还有application.properties中相关的feign client配置信息
  2. 生成Feign.client()，默认为LoadBalancerFeignClient
  3. 生成默认Targter对象：HystrixTargter
  4. builder、client、targter 通过JDK动态代理生成feign动态代理对象

一张图总结：

申明

本文章首发自本人博客：https://www.cnblogs.com/wang-meng 和公众号：壹枝花算不算浪漫，如若转载请标明来源!

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