1.增加 useGeneratedKeys="true" keyProperty="id"这两个参数的配置

 <insert id="save" useGeneratedKeys="true" keyProperty="id">
        INSERT INTO
        sys_student (name,chinese,mathematics,english)
        VALUES
        (#{name},#{chinese},#{mathematics},#{english})
    </insert>

2.复写save方法

 long save(Student student);

 3.业务层定义一个方法,获取返回的Id