springboot:@Configuration中注解的类里还有@Configuration如何理解？

@CompileStatic

@Configuration

class FeignAutoConfiguration {



  @Configuration

  @ConditionalOnClass(OkHttpClient.class)

  @ConditionalOnMissingClass("com.netflix.loadbalancer.ILoadBalancer")

  @ConditionalOnProperty(value = "feign.okhttp.enabled")

  protected static class OkHttpFeignConfiguration {

    @Bean

    @ConditionalOnMissingBean(ConnectionPool.class)

    ConnectionPool httpClientConnectionPool(FeignHttpClientProperties httpClientProperties,                                            

    OkHttpClientConnectionPoolFactory connectionPoolFactory) {

        Integer maxTotalCOnnections= httpClientProperties.getMaxConnections()

        Long timeToLive = httpClientProperties.getTimeToLive()

        TimeUnit ttlUnit = httpClientProperties.getTimeToLiveUnit()

        return connectionPoolFactory.create(maxTotalConnections, timeToLive, ttlUnit)

    }

   

    @ConditionalOnMissingBean(okhttp3.OkHttpClient.class)

    okhttp3.OkHttpClient client(OkHttpClientFactory httpClientFactory,

                                ConnectionPool connectionPool,

                                FeignHttpClientProperties httpClientProperties) {

        Boolean followRedirects = httpClientProperties.isFollowRedirects()

        Boolean disableSslValidation = httpClientProperties.isDisableSslValidation()

        this.okHttpClient = httpClientFactory.createBuilder(disableSslValidation).

            connectTimeout(5000L, TimeUnit.MILLISECONDS).

            readTimeout(60000L, TimeUnit.MILLISECONDS).

            followRedirects(followRedirects).

            connectionPool(connectionPool).build()

        return this.okHttpClient

    }

   

    ...

    ...

  }  

}