Ribbon服务实现不同服务，不同配置是通过@RibbonClient和RibbonClients两个注解来实现的。@RibbonClient注册的某个Client配置类。@RibbonClients注册的全局默认配置类。

Feign实现不同服务，不同配置，是根据FeignClient来获取自定义的配置。

示例

定义Ribbon配置类

public class AppRibbonConfig {

    @Bean
    public IPing iping() {
        return new DummyPing();
    }
}

启动类上添加注解

@RibbonClient(name = "app-provider", configuration = AppRibbonConfig.class)

源码解析

@RibbonClient和@RibbonClients

这两个注解的功能都是引入RibbonClientConfigurationRegistrar，该类主要是生成RibbonClientSpecification的BeanDefinition。

RibbonAutoConfiguration

该类会获取到所有的RibbonClientSpecification，设置到SpringClientFactory的map集合中。

public class RibbonAutoConfiguration {
    @Autowired(
        required = false
    )
    private List<RibbonClientSpecification> configurations = new ArrayList();
    @Autowired
    private RibbonEagerLoadProperties ribbonEagerLoadProperties;

    public RibbonAutoConfiguration() {
    }

    @Bean
    public HasFeatures ribbonFeature() {
        return HasFeatures.namedFeature("Ribbon", Ribbon.class);
    }

    @Bean
    public SpringClientFactory springClientFactory() {
        SpringClientFactory factory = new SpringClientFactory();
        factory.setConfigurations(this.configurations);
        return factory;
    }
}

系统中默认的配置有RibbonAutoConfiguration和RibbonEurekaAutoConfiguration，RibbonEurekaAutoConfiguration类上的注解上含有配置类，EurekaRibbonClientConfiguration。

@Configuration
@EnableConfigurationProperties
@ConditionalOnRibbonAndEurekaEnabled
@AutoConfigureAfter({RibbonAutoConfiguration.class})
@RibbonClients(
    defaultConfiguration = {EurekaRibbonClientConfiguration.class}
)
public class RibbonEurekaAutoConfiguration {
    public RibbonEurekaAutoConfiguration() {
    }
}

@EnableFeignClients

该类会注册FeignClientSpecification。FeignClientsRegistrar#registerBeanDefinitions，会加载默认配置和对应的FeignClient服务名的配置。

    public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        this.registerDefaultConfiguration(metadata, registry);
        this.registerFeignClients(metadata, registry);
    }

    private void registerDefaultConfiguration(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        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();
            }

            this.registerClientConfiguration(registry, name, defaultAttrs.get("defaultConfiguration"));
        }

    }

    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());
    }

FeignAutoConfiguration

FeignAutoConfiguration会获取到FeignClientSpecification

@Configuration
@ConditionalOnClass({Feign.class})
@EnableConfigurationProperties({FeignClientProperties.class, FeignHttpClientProperties.class})
public class FeignAutoConfiguration {
    @Autowired(
        required = false
    )
    private List<FeignClientSpecification> configurations = new ArrayList();

    public FeignAutoConfiguration() {
    }

    @Bean
    public HasFeatures feignFeature() {
        return HasFeatures.namedFeature("Feign", Feign.class);
    }

    @Bean
    public FeignContext feignContext() {
        FeignContext context = new FeignContext();
        context.setConfigurations(this.configurations);
        return context;
    }

FeignClientFactoryBean

系统启动的时候，会加载FeignClientFactoryBean，会执行FeignClientFactoryBean#getObject，获取到context对象，从而获取相应的组件。

    protected Builder feign(FeignContext context) {
        FeignLoggerFactory loggerFactory = (FeignLoggerFactory)this.get(context, FeignLoggerFactory.class);
        Logger logger = loggerFactory.create(this.type);
        Builder builder = ((Builder)this.get(context, Builder.class)).logger(logger).encoder((Encoder)this.get(context, Encoder.class)).decoder((Decoder)this.get(context, Decoder.class)).contract((Contract)this.get(context, Contract.class));
        this.configureFeign(context, builder);
        return builder;
    }

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

第一次访问服务

Ribbon是懒加载的，NamedContextFactory#getContext，第一次访问是没有context对象的，所以会进行创建。

    protected AnnotationConfigApplicationContext getContext(String name) {
        if (!this.contexts.containsKey(name)) {
            synchronized(this.contexts) {
                if (!this.contexts.containsKey(name)) {
                    this.contexts.put(name, this.createContext(name));
                }
            }
        }

        return (AnnotationConfigApplicationContext)this.contexts.get(name);
    }

NamedContextFactory#createContext，根据服务配置生成对应的AnnotationConfigApplicationContext

    protected AnnotationConfigApplicationContext createContext(String name) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
        if (this.configurations.containsKey(name)) {
            Class[] var3 = ((NamedContextFactory.Specification)this.configurations.get(name)).getConfiguration();
            int var4 = var3.length;

            for(int var5 = 0; var5 < var4; ++var5) {
                Class<?> configuration = var3[var5];
                context.register(new Class[]{configuration});
            }
        }

        Iterator var9 = this.configurations.entrySet().iterator();

        while(true) {
            Entry entry;
            do {
                if (!var9.hasNext()) {
                    context.register(new Class[]{PropertyPlaceholderAutoConfiguration.class, this.defaultConfigType});
                    context.getEnvironment().getPropertySources().addFirst(new MapPropertySource(this.propertySourceName, Collections.singletonMap(this.propertyName, name)));
                    if (this.parent != null) {
                        context.setParent(this.parent);
                        context.setClassLoader(this.parent.getClassLoader());
                    }

                    context.setDisplayName(this.generateDisplayName(name));
                    context.refresh();
                    return context;
                }

                entry = (Entry)var9.next();
            } while(!((String)entry.getKey()).startsWith("default."));

            Class[] var11 = ((NamedContextFactory.Specification)entry.getValue()).getConfiguration();
            int var12 = var11.length;

            for(int var7 = 0; var7 < var12; ++var7) {
                Class<?> configuration = var11[var7];
                context.register(new Class[]{configuration});
            }
        }
    }

Ribbon提前加载

ribbon:
  eager-load:
    clients: app-provider
    enabled: true

在RibbonAutoConfiguration中会根据配置判断是否生成对象ribbonApplicationContextInitializer

@Bean
@ConditionalOnProperty({"ribbon.eager-load.enabled"})
public RibbonApplicationContextInitializer ribbonApplicationContextInitializer() {
    return new RibbonApplicationContextInitializer(this.springClientFactory(), this.ribbonEagerLoadProperties.getClients());
}

RibbonApplicationContextInitializer#initialize，该类主要是根据配置的clients数据对相应的服务进行加载

protected void initialize() {
    if (this.clientNames != null) {
        Iterator var1 = this.clientNames.iterator();

        while(var1.hasNext()) {
            String clientName = (String)var1.next();
            this.springClientFactory.getContext(clientName);
        }
    }
}