Returning values from MyBatis <insert> mapped methods

You can use as follows. In xml

 <insert id="insertNewUser" parameterType="User">
            <selectKey keyProperty="userId" resultType="Integer" order="BEFORE">
                select NEXTVAL('base.user_id_seq')
            </selectKey>
            INSERT INTO base.user(
                user_id, user_name)
            VALUES (#{userId}, #{userName});
    </insert>

In Java class from where you have called the method to insert, you can get the value by calling user.getUserId().

Basically the next val is stored inside the variable of the object. Here userId inside User.

The return type of mapped insert method can be void or int (in which case it will return the number of the inserted row). You can do the following mechanism to return the generated id:

<insert id="insert" parameterClass="MyParameter">
  <selectKey order="AFTER" keyProperty="id" resultType="long">
    SELECT currval('my_seq')
  </selectKey>
  INSERT INTO mytable(col1, col2) VALUES (#{val1}, #{val2})
</insert>

This will set generated id column to id property of your parameter class. After that, object you passed as parameter will have generated id set in its property.