解决pageHelper分页失效以及如何配置问题

@Configuration
public class MybatisConfig {
   @Bean
   public PageHelper pageHelper() {
      PageHelper pageHelper = new PageHelper();
      Properties p = new Properties();
      p.setProperty("offsetAsPageNum", "true");
      p.setProperty("rowBoundsWithCount", "true");
      p.setProperty("reasonable", "true");
      pageHelper.setProperties(p);
      return pageHelper;
   }
}

<select id="selectAll" resultMap="BaseResultMap">
        SELECT * FROM student;
</select>

 <select id="selectAll" resultMap="BaseResultMap">
        SELECT * FROM student
</select>

List<Student> students = studentMapper.selectAll();
PageHelper.startPage(1, 5, true);

PageHelper.startPage(1, 5, true);
List<Student> students = studentMapper.selectAll();