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操作步骤如下：
1. k8s环境下，consumer端开启mesh模式
2. consumer端需要调用多个provider
3. provider有应用级注册和接口级注册，并且需要的provider不再同一个namespace下
4. 原有项目存在dubbo2.6与3.1多版本间的相互调用，在开启消费端mesh（dubbo3.1）后，无法调用到2.6的服务提供者

**问题：**

1. 如何实现在一个consumer下，调用多个namespace下的provider，并且provider有应用级注册和接口级注册
2. dubbo3.1消费端在开启mesh后，如何调用版本是2.6的服务提供者
import java.lang.annotation.Target;
/**
 * An annotation used for referencing a Dubbo service.
 * <p>
 * <b>It is recommended to use @DubboReference on the @Bean method in the Java-config class, but not on the fields or setter methods to be injected.</b>
 * </p>
 * <p>
 * Step 1: Register ReferenceBean in Java-config class:
 * <pre class="code">
 * &#64;Configuration
 * public class ReferenceConfiguration {
 *     &#64;Bean
 *     &#64;DubboReference(group = "demo")
 *     public ReferenceBean&lt;HelloService&gt; helloService() {
 *         return new ReferenceBean();
 *     }
 *
 *     &#64;Bean
 *     &#64;DubboReference(group = "demo", interfaceClass = HelloService.class)
 *     public ReferenceBean&lt;GenericService&gt; genericHelloService() {
 *         return new ReferenceBean();
 *     }
 * }
 * </pre>
 * <p>
 * Step 2: Inject ReferenceBean by @Autowired
 * <pre class="code">
 * public class FooController {
 *     &#64;Autowired
 *     private HelloService helloService;