The solution of java.lang.UnsupportedOperationException anomaly of MyBatis

Today, when you use MyBatis to execute an SQL statement, the following exception occurs:

The SQL statement configuration information executed is as follows:

<select id= "Getcolumnsbytablename" parametertype= "String" resulttype= "java.util.List" >
Select T.column_name from User_tab_columns t where T.tablename=#{tablename,jdbctype=varchar}
</select>

The corresponding DAO interface code is:

Public list<string> Getcolumnsbytablename (String tablename);

should read:

<select id= "Getcolumnsbytablename" parametertype= "string" resulttype= "string" > select T.column_name F Rom User_tab_columns t where t.tablename=#{tablename,jdbctype=varchar}</select>

The reason is that Resulttype represents the element type in the list, not the list itself, because the method declaration in DAO (marked red out)

Public list<string> getcolumnsbytablename (String tablename);

to confuse.

Remember: Resulttype returns the element type in the collection, not the collection itself