Feign之重复出现的FeignClientSpecification

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场景复现

依赖:

  1. Spring Boot 2.1.6.RELEASE
  2. Eureka Client 2.1.0.RELEASE
  3. OpenFeign 2.1.0.RELEASE

我们创建两个项目, ahao-server服务提供方和ahao-client服务调用方.
Eureka可以使用我弄的一个开箱即用Eureka

在ahao-server创建一个显示当前时间的controller, 同时注册到eureka上.
假设端口为http://localhost:8080

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@RestController
@RequestMapping("/ahao")
public class TimeController {
    @RequestMapping("/date")
    public String date() { return "现在日期是:" + new SimpleDateFormat("yyyy年MM月dd日").format(new Date()); }
    
    @RequestMapping("/time")
    public String time() { return "现在时间是:" + new SimpleDateFormat("hh时mm分ss秒").format(new Date()); }
}

在ahao-client创建一个controller和两个feign客户端, 同时注册到eureka上.
假设端口为http://localhost:8081

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@RestController
@RequestMapping("/ahao")
public class TimeController {
    @Autowired private DateApi dateApi;
    @Autowired private TimeApi timeApi;
    @RequestMapping("/date")
    public String date() { return dateApi.date(); }
    @RequestMapping("/time")
    public String time() { return timeApi.time(); }
}


@FeignClient(value = "AHAO-SERVER", path = "/ahao")
public interface DateApi {
    @RequestMapping("/date") String date();
}
@FeignClient(value = "AHAO-SERVER", path = "/ahao")
public interface TimeApi {
    @RequestMapping("/time") String time();
}

运行ahao-client报错

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***************************
APPLICATION FAILED TO START
***************************
Description:
The bean 'AHAO-SERVER.FeignClientSpecification', defined in null, could not be registered. A bean with that name has already been defined in null and overriding is disabled.

Action:
Consider renaming one of the beans or enabling overriding by setting spring.main.allow-bean-definition-overriding=true

Process finished with exit code 1

这个叫做AHAO-SERVER.FeignClientSpecification的Bean是从哪来的???

问题所在

Spring打印出了异常堆栈. 我们跟进去看一下.

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// org.springframework.cloud.openfeign.FeignClientsRegistrar
class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {
    private void registerClientConfiguration(BeanDefinitionRegistry registry, Object name, Object configuration) {
        // 省略部分代码
        registry.registerBeanDefinition(name + "." + FeignClientSpecification.class.getSimpleName(), builder.getBeanDefinition());
    }
}

我们可以看到, 这里注册了一个Bean, 名字就是AHAO-SERVER.FeignClientSpecification.
这个name是从外部传进来的.

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// org.springframework.cloud.openfeign.FeignClientsRegistrar
class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {
    public void registerFeignClients(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        // 省略部分代码
        Map<String, Object> attributes = annotationMetadata.getAnnotationAttributes(FeignClient.class.getCanonicalName());
        
        String name = getClientName(attributes);
        registerClientConfiguration(registry, name, attributes.get("configuration"));

        registerFeignClient(registry, annotationMetadata, attributes);
        // 省略部分代码
    }
}

可以看到, name应该是从注解中的属性取值来的, 再看看getClientName()方法.

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// org.springframework.cloud.openfeign.FeignClientsRegistrar
class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {
    private String getClientName(Map<String, Object> client) {
        if (client == null) { return null; }
        
        String value = (String) client.get("contextId");
        if (!StringUtils.hasText(value)) { value = (String) client.get("value"); }
        if (!StringUtils.hasText(value)) { value = (String) client.get("name"); }
        if (!StringUtils.hasText(value)) { value = (String) client.get("serviceId"); }
        if (StringUtils.hasText(value)) { return value; }
        throw new IllegalStateException("Either 'name' or 'value' must be provided in @" + FeignClient.class.getSimpleName());
    }
}

一目了然了, 我们声明@FeignClient注解时, 只使用了value属性, 所以产生了冲突, 只要加上contextId就好了.

解决方案

加上contextId属性即可.

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@FeignClient(value = "AHAO-SERVER", path = "/ahao", contextId = "AHAO-SERVER-DATE")
public interface DateApi {
    @RequestMapping("/date") String date();
}
@FeignClient(value = "AHAO-SERVER", path = "/ahao", contextId = "AHAO-SERVER-TIME")
public interface TimeApi {
    @RequestMapping("/time") String time();
}

Spring Boot/Cloud 2.0.x 版本

我们切换到Spring Boot/Cloud 2.0.x版本, 发现没有contextId属性, 但是启动的时候可以正常启动, 不会报错Bean冲突.
看下Spring Boot/Cloud 2.0.x版本的源码.

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// org.springframework.cloud.openfeign.FeignClientsRegistrar
class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {
    private String getClientName(Map<String, Object> client) {
        if (client == null) { return null; }
        
        String value = (String) client.get("value");
        if (!StringUtils.hasText(value)) { value = (String) client.get("name"); }
        if (!StringUtils.hasText(value)) { value = (String) client.get("serviceId"); }
        if (StringUtils.hasText(value)) { return value; }
        throw new IllegalStateException("Either 'name' or 'value' must be provided in @" + FeignClient.class.getSimpleName());
    }
}

看下getClientName()方法, 里面也没有使用contextId. 也就是会创建两个同名AHAO-SERVER.FeignClientSpecification的Bean.
后来翻了下issue发现了答案.

spring boot 2.0.x
spring.main.allow-bean-definition-overriding default value is “true”
spring boot 2.1.x default value changed to “false”

原来是允许Bean重复定义所以才没有报错. 关键在spring.main.allow-bean-definition-overriding这个属性.

  • Spring Boot 2.0.x 默认是 true.
  • Spring Boot 2.1.x 默认是 false.

参考资料