使用nacos动态刷新数据源导致seata异常

问题出现

在执行有@GlobalTransactional的方法时会报错，并且看起来特别不应该

### Cause: java.lang.ClassCastException: io.seata.rm.datasource.ConnectionProxy cannot be cast to com.alibaba.druid.pool.DruidPooledConnection
    at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30) ~[mybatis-3.5.5.jar!/:3.5.5]
    at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:199) ~[mybatis-3.5.5.jar!/:3.5.5]
    at org.apache.ibatis.session.defaults.DefaultSqlSession.insert(DefaultSqlSession.java:184) ~[mybatis-3.5.5.jar!/:3.5.5]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_275]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_275]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_275]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_275]
    at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:426) ~[mybatis-spring-2.0.5.jar!/:2.0.5]
    ... 116 common frames omitted
Caused by: java.lang.ClassCastException: io.seata.rm.datasource.ConnectionProxy cannot be cast to com.alibaba.druid.pool.DruidPooledConnection
    at com.alibaba.druid.pool.DruidDataSource$$EnhancerBySpringCGLIB$$471c5033.getConnection() ~[druid-1.1.23.jar!/:1.1.23]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_275]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_275]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_275]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_275]
    at org.springframework.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:282) ~[spring-core-5.2.8.RELEASE.jar!/:5.2.8.RELEASE]
    at org.springframework.cloud.context.scope.GenericScope$LockedScopedProxyFactoryBean.invoke(GenericScope.java:499) ~[spring-cloud-context-2.2.2.RELEASE.jar!/:2.2.2.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.8.RELEASE.jar!/:5.2.8.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749) ~[spring-aop-5.2.8.RELEASE.jar!/:5.2.8.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:691) ~[spring-aop-5.2.8.RELEASE.jar!/:5.2.8.RELEASE]
    at com.alibaba.druid.pool.DruidDataSource$$EnhancerBySpringCGLIB$$5dcd2647.getConnection() ~[druid-1.1.23.jar!/:1.1.23]
    at org.springframework.jdbc.datasource.DataSourceUtils.fetchConnection(DataSourceUtils.java:158) ~[spring-jdbc-5.2.8.RELEASE.jar!/:5.2.8.RELEASE]
    at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:116) ~[spring-jdbc-5.2.8.RELEASE.jar!/:5.2.8.RELEASE]
    at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:79) ~[spring-jdbc-5.2.8.RELEASE.jar!/:5.2.8.RELEASE]
    at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:80) ~[mybatis-spring-2.0.5.jar!/:2.0.5]
    at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:67) ~[mybatis-spring-2.0.5.jar!/:2.0.5]
    at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:337) ~[mybatis-3.5.5.jar!/:3.5.5]
    at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:86) ~[mybatis-3.5.5.jar!/:3.5.5]
    at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:49) ~[mybatis-3.5.5.jar!/:3.5.5]
    at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:117) ~[mybatis-3.5.5.jar!/:3.5.5]
    at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:76) ~[mybatis-3.5.5.jar!/:3.5.5]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_275]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_275]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_275]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_275]
    at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49) ~[mybatis-3.5.5.jar!/:3.5.5]
    at com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor.intercept(MybatisPlusInterceptor.java:82) ~[mybatis-plus-extension-3.4.0.jar!/:3.4.0]
    at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) ~[mybatis-3.5.5.jar!/:3.5.5]
    at com.sun.proxy.$Proxy249.update(Unknown Source) ~[na:na]
    at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:197) ~[mybatis-3.5.5.jar!/:3.5.5]
    ... 122 common frames omitted

在异常中能看到是获取connection出现了类不一致问题，接下来开始埋坑。。。

猜想

seata在开始保存代理数据源时有问题，导致在获取connection时爆出异常；然后就是漫长的查找debug时间，最后发现在获取connection时，seata一点问题也没有0.0

后来发现正常系统的datasource和有问题的datasource代理内容不一致，而且有问题的datasource是一个代理对象，再次猜想：代理中包裹着代理，导致异常出现

结果

@RefreshScope 设置到了DruidDataSource上，导致DruidDataSource被cglib动态代理

在执行getConnection时，先是cglib的GenericScope.invoke执行了ReflectionUtils.invokeMethod使用了反射，导致getConnection获取的类是DruidPooledConnection而不是接口Connection，接下来被seata再次代理（SeataAutoDataSourceProxyAdvice）得到的类变成了ConnectionProxy，返回后导致出现ClassCastException异常