1, At that time, when I made a joint query table , adopt xml Configuring joint table query is particularly difficult , I've asked several people, but I can't . Then I asked a big man , Teaching me how to use annotation configuration is very simple , It is hereby recorded .(xml And annotations can be mixed , Annotation configuration is recommended ,xml Once configured, restart tomcat, Too long , When changing the annotation configuration , Just republish it , It takes less time )
@Select("select * from class where id not in(select cid from classchoice where
name=#{name})and id not in(select cid from examine where name=#{name}) and
id!=1 and num>0" ) List<Class> queryMyChoiceClassNotChoiced(String name);
  Equivalent to the following
select * from class where id not in( select cid from classchoice where
name=#{name} ) and id not in( select cid from examine where name=#{name} ) and
id!=1 and num>0

2,tomcat When making the welcome interface ,welcome It doesn't work . Later, through direct configuration tomcat of url Realized