spring boot整合mybatis、mybatis-plus进行分页查询

1、 spring boot整合mybatis分页

首先自定义业务层分页对象

/**
 * 借助此类封装业务层分页信息
 * 建议：所有用于封装数据的对象都实现Servializable接口（此接口是对象
 * 是否可以序列化的标识）
 * FAQ？
 * 1、何为序列化和反序列
 * 1）序列化：将对象转换为字节
 * 2）反序列化：将字节转化为对象
 * 2、序列化和反序列化应用场景
 * 1）将对象转换为字节存储到内存或文件
 * 2）将对象转为字节通过网络进行传输
 * 3）java中对象的序列化实现
 * 1）ObjectOutputStream(用于将对象序列化)
 * 2）ObjectInputStream(将字节反序列化为对象)
 * @param 
 */
@Data
public class PageObject<T> implements Serializable {
    //序列化和反序列化操作时的唯一标识，建议只要实现序列化接口，都要手动添加这个id
    private static final long serialVersionUID = -3130527491950235344L;
    /**总记录数*/
    private Integer rowCount;
    /**当前页记录*/
    private List<T> records;
    /**总页数*/
    private Integer pageCount;
    /**页面大小（每页最多显示多少条记录）*/
    private Integer pageSize;
    /**页码值*/
    private Integer pageCurrent;

    public PageObject() {}

    public PageObject(Integer rowCount, List<T> records, Integer pageSize, Integer pageCurrent) {
        this.rowCount = rowCount;
        this.records = records;
        this.pageSize = pageSize;
        this.pageCurrent = pageCurrent;
        this.pageCount = this.rowCount/this.pageSize;
        if (this.rowCount%this.pageSize!=0)
            this.pageCount++;
    }
}

mapper.xml写sql语句

<!--基于条件查询当前页记录    -->
    <select id="findPageObjects" resultType="com.cy.pj.sys.pojo.SysLog">
        select *
        <include refid="queryWhere"/>
        order by createdTime desc
        limit #{startIndex},#{pageSize}
    </select>

    <!--    基于条件查询总记录数-->
    <select id="getRowCount" resultType="int">
        select count(*)
        <include refid="queryWhere"/>
    </select>

    <!-- 通过sql元素提取共性   -->
    <sql id="queryWhere">
        from sys_logs
        <where>
            <if test="username!=null and username!=''">
                username like concat("%",#{username},"%")
            </if>
        </where>
    </sql>

业务层

@Override
    public PageObject<SysLog> findPageObjects(String username, Integer pageCurrent) {
        //1、对参数进行校验（可以自己校验，也可以借助框架：spring validation）
        if (pageCurrent == null || pageCurrent < 1)
            throw new IllegalArgumentException("页码值不合法");//无效的参数异常
        //2、基于查询条件查询总记录数
        int rowCount = sysLogDao.getRowCount(username);
        if (rowCount == 0)
            throw new ServiceException("没有找到对应的记录");
        //3查询当前页记录
        int pageSize = 5;//页面大小，每页最多显示多少条记录
        int startIndex = (pageCurrent - 1) * pageSize;//当前页起始位置
        List<SysLog> records = sysLogDao.findPageObjects(username, startIndex, pageSize);
        //4、封装查询结果
//        PageObject pageObject=new PageObject<>();
//        pageObject.setRowCount(rowCount);
//        pageObject.setRecords(records);
//        pageObject.setPageSize(pageSize);
//        pageObject.setPageCurrent(pageCurrent);
//        pageObject.setPageCount(rowCount/pageSize);
//        if (rowCount/pageSize!=0){
//            Integer pageCount = pageObject.getPageCount();
//            pageCount++;
//        }
        PageObject<SysLog> pageObject = new PageObject<>(rowCount, records, pageSize, pageCurrent);
        return pageObject;
    }

控制层

 @Autowired
    private SysLogService sysLogService;

    @GetMapping("doFindPageObjects")
    public JsonResult doFindPageObjects(String username, Integer pageCurrent) {
        PageObject<SysLog> pageObjects = sysLogService.findPageObjects(username, pageCurrent);
        return new JsonResult(pageObjects);
    }

2、spring boot整合mybatis使用分页插件PageHelper

pom文件添加jar包

<dependency>
 <groupId>com.github.pagehelper</groupId>
 <artifactId>pagehelper-spring-boot-starter</artifactId> 
 <version>1.3.0</version>
</dependency>

Pojo对象设计及实现
创建SysUser类型,基于此类型的对象封装用户信息,关键代码如下:

package com.cy.pj.sys.pojo;
 @Data
  public class SysUser implements Serializable { 
  private static final long serialVersionUID = -8248568398323868047L; 
  private Integer id; 
  private String username; 
  private String password; 
  private String salt; 
  private String mobile; 
  private String email; 
  private Integer valid; 
  private Integer deptId; 
  private String deptName; 
  private Date createdTime; 
  private Date modifiedTime; 
  private String createdUser; 
  private String modifiedUser; }

Dao 接口及方法设计
第一步:创建SysUserDao接口及方法,用于实现分页查询,关键代码如下:

package com.cy.pj.sys.dao; 
@Mapper 
public interface SysUserDao{ 
List<SysUser> findPageObjects(String username); }

第二步:创建SysUserMapper映射文件并添加分页查询SQL映射,关键代码如下:

<mapper namespace="com.cy.pj.sys.dao.SysUserDao"> 
<select id="findPageObjects" resultType="com.cy.pj.sys.pojo.SysUser">
 select u.*,d.name deptName from sys_users u left join sys_depts d on u.deptId=d.id <where>
  <if test="username!=null and username!=''"> 
  u.username like concat ("%",#{username},"%") </if> 
  </where> order by u.createdTime desc </select> 
  </mapper>

Service 接口及方法设计

package com.cy.pj.sys.service.impl;
 @Service 
 public class SysUserServiceImpl implements SysUserService{
  @Autowired private SysUserDao sysUserDao; 
  public PageObject<SysUser> findPageObjects(String username, Integer pageCurrent){ 
  int pageSize=5;
  //使用PageHelper封装分页信息
   Page<SysUser> page=PageHelper.startPage(pageCurrent,pageSize); 
   List<SysUser> records=sysUserDao.findPageObjects(username); 
   //PageObject为自定类，封装了查询到的分页内容
   return new PageObject((int)page.getTotal(),records, pageSize,pageCurrent); } }

Controller类及方法设计

@Autowired 
private SysUserService sysUserService; 
@GetMapping("doFindPageObjects") 
public JsonResult doFindPageObjects(String username, Integer pageCurrent){ 
PageObject<SysUser> pageObject= sysUserService.findPageObjects(username,pageCurrent); 
return new JsonResult(pageObject);
 }

3、spring boot整合mybatis-plus分页

业务层完成分页查询
查询到的分页信息直接从IPage中获取

//封装分页信息，第一个参数页码值、第二个参数每页显示数量
//IPage iPage = new Page(pageNum, pageSize);
		Page<Users> pages = new Page<Users>(pageNum, pageSize);
		//进行分页查询
		//iPage = usersMapper.selectPage(pages, queryWrapper);
		IPage<Users> iPage = usersMapper.selectPage(pages, queryWrapper);
		//获取分页查询记录
		List<Users> data = iPage.getRecords();
		//获取总记录
		long count = iPage.getTotal();

编辑分页配置类

@Configuration  //标识配置文件
public class MybatisPlusConfig {

    @Bean       //将数据交给spring容器管理
    public PaginationInterceptor paginationInterceptor() {
        PaginationInterceptor paginationInterceptor = new PaginationInterceptor();
        // 设置请求的页面大于最大页后操作， true调回到首页，false 继续请求  默认false
        paginationInterceptor.setOverflow(true);
        // 设置最大单页限制数量，默认 500 条，-1 不受限制
        // paginationInterceptor.setLimit(500);
        // 开启 count 的 join 优化,只针对部分 left join
        paginationInterceptor.setCountSqlParser(new JsqlParserCountOptimize(true));
        return paginationInterceptor;
    }
}