Mapper中

public interface StudentMapper {

    @Select("select * from students")
    List<Students> findAll();

    @Insert("insert into students (sid,username,major,dnum) values (#{sid},#{username},#{major},#{dnum})")
    void addStudent(Students students);

    @Delete("delete from students where id=#{id}")
    void delStudentById(Integer id);

    @SelectProvider(type = StudentProvider.class, method = "findStudentByManyCondition")
    List<Students> findByManyCondition(Students students);
}

对应的Provider类

public class StudentProvider {

    public String findStudentByManyCondition(Students students){

        StringBuffer sql = new StringBuffer("select * from students where 1=1");

        String sid, username, major, dnum;
        sid = students.getSid();
        username = students.getUsername();
        major = students.getMajor();
        dnum = students.getDnum();

        if(!"".equals(sid)){
            sql.append(" and sid='"+sid+ "'");
        }

        if(!"".equals(username)){
            sql.append(" and username='"+username+ "'");
        }

        if(!"".equals(major)){
            sql.append(" and major='"+major+ "'");
        }

        if(!"".equals(dnum)){
            sql.append(" and dnum='"+dnum+ "'");
        }

        return sql.toString();
    }
}