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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.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import static org.apache.dubbo.common.constants.CommonConstants.ANY_VALUE;
import static org.apache.dubbo.common.constants.CommonConstants.CLUSTER_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.COMMA_SEPARATOR;
import static org.apache.dubbo.common.constants.CommonConstants.COMMA_SEPARATOR_CHAR;
import static org.apache.dubbo.common.constants.CommonConstants.CONSUMER_SIDE;
import static org.apache.dubbo.common.constants.CommonConstants.DEFAULT_CLUSTER_DOMAIN;
import static org.apache.dubbo.common.constants.CommonConstants.DEFAULT_MESH_PORT;
import static org.apache.dubbo.common.constants.CommonConstants.INTERFACE_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.LOCALHOST_VALUE;
import static org.apache.dubbo.common.constants.CommonConstants.MESH_ENABLE;
import static org.apache.dubbo.common.constants.CommonConstants.METHODS_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.MONITOR_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.PROXY_CLASS_REF;
import static org.apache.dubbo.common.constants.CommonConstants.REVISION_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.SEMICOLON_SPLIT_PATTERN;
import static org.apache.dubbo.common.constants.CommonConstants.SIDE_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.SVC;
import static org.apache.dubbo.common.constants.CommonConstants.TRIPLE;
import static org.apache.dubbo.common.constants.CommonConstants.UNLOAD_CLUSTER_RELATED;
import static org.apache.dubbo.common.constants.LoggerCodeConstants.CLUSTER_NO_VALID_PROVIDER;
import static org.apache.dubbo.common.constants.LoggerCodeConstants.CONFIG_FAILED_DESTROY_INVOKER;
import static org.apache.dubbo.common.constants.LoggerCodeConstants.CONFIG_NO_METHOD_FOUND;