问题：Error querying database. Cause: org.apache.ibatis.binding.BindingException: Parameter ‘username‘

异常问题：

org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: org.apache.ibatis.binding.BindingException: Parameter 'username' not found. Available parameters are [arg1, arg0, param1, param2]
### Cause: org.apache.ibatis.binding.BindingException: Parameter 'username' not found. Available parameters are [arg1, arg0, param1, param2]

产生原因：

当出现多个参数时，mybatis会将这些参数封存到map集合里面，故需要使用mybatis提供的参数来获取[arg1, arg0, param1, param2]

解决方法：

将原来mapper.xml文件中的

select * from admin where username=#{username} and password=#{password}

改为

select * from admin where username=#{arg0} and password=#{arg1}

或者

select * from admin where username=#{param1} and password=#{param2}

亦或者

select * from admin where username=#{arg0} and password=#{param2}

select * from admin where username=#{param1} and password=#{arg1}