mybatis实现分页查询-自己封装分页方法

大致结构如下：

一、定义返回数据结构

创建返回数据结构主要是为了统一方便，和分页查询的关系并不大，也可以忽略这一步。

package boc.ljh.config;import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;@ApiModel("返回数据结构")
public class Result<T> {@ApiModelProperty("返回状态")private Integer status;@ApiModelProperty("返回信息")private String message;@ApiModelProperty("返回数据")private T date;public String getMessage() {return message;}public Integer getStatus() {return status;}public void setStatus(Integer status) {this.status = status;}public void setMessage(String message) {this.message = message;}public T getDate() {return date;}public void setDate(T date) {this.date = date;}
}

二、封装分页查询类

package boc.ljh.config;import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;import java.util.List;@ApiModel("分页与查询")
public class PaginationHelper<T,O> {@ApiModelProperty("开始记录索引")private int start;@ApiModelProperty("当前页码")private int pageNum;@ApiModelProperty("每页条数")private int pageSize;@ApiModelProperty("数据总条数")private int totalSize;@ApiModelProperty("总页数")private int totalPages;@ApiModelProperty("查询参数")private O options;@ApiModelProperty("返回的数据")private List<T> data;public int getStart() {if(pageNum==0){pageNum=1;}start = this.getPageSize() * (pageNum-1);return start;}public void setStart(Integer start) {this.start = start;}public void setStart(int start) {this.start = start;}public int getPageNum() {return pageNum;}public void setPageNum(int pageNum) {this.pageNum = pageNum;}public int getPageSize() {return pageSize;}public void setPageSize(int pageSize) {this.pageSize = pageSize;}public int getTotalSize() {return totalSize;}public void setTotalSize(int totalSize) {this.totalSize = totalSize;}public int getTotalPages() {return totalPages;}public void setTotalPages(int totalPages) {this.totalPages = totalPages;}public O getOptions() {return options;}public void setOptions(O options) {this.options = options;}public List<T> getData() {return data;}public void setData(List<T> data) {this.data = data;}
}

三、dao、service、controller层

dao：

package boc.ljh.dao;import boc.ljh.config.PaginationHelper;
import boc.ljh.pojo.User;import javax.jws.soap.SOAPBinding;
import java.util.List;public interface UserDao {//获取用户列表List<User> loadAllUserInfo(PaginationHelper paginationHelper);//获取数据条数Integer loadAllUserCount();
}

service：

package boc.ljh.service;import boc.ljh.config.PaginationHelper;
import boc.ljh.pojo.User;
import org.apache.ibatis.annotations.Select;
import org.omg.CORBA.INTERNAL;
import org.springframework.stereotype.Service;import java.util.List;@Service
public interface UserService {//获取用户列表List<User> loadAllUserInfo(PaginationHelper paginationHelper);//获取数据条数Integer loadAllUserCount();
}

serviceImpl：

package boc.ljh.service;import boc.ljh.config.PaginationHelper;
import boc.ljh.dao.UserDao;
import boc.ljh.pojo.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;import javax.annotation.Resource;
import java.util.List;@Service
public class UserServiceImpl implements UserService {@Resourceprivate UserDao userDao;@Overridepublic List<User> loadAllUserInfo(PaginationHelper paginationHelper) {return userDao.loadAllUserInfo(paginationHelper);}@Overridepublic Integer loadAllUserCount() {return userDao.loadAllUserCount();}
}

xml：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="boc.ljh.dao.UserDao"><resultMap id="BaseResultMap" type="boc.ljh.pojo.User"><id column="user_id" jdbcType="INTEGER" property="userId"/><result column="user_name" jdbcType="VARCHAR" property="userName"/><result column="user_age" jdbcType="INTEGER" property="userAge"/></resultMap><select id="loadAllUserInfo" parameterType="boc.ljh.config.PaginationHelper" resultMap="BaseResultMap">select * from user order by user_id ASC limit #{start},#{pageSize}</select><select id="loadAllUserCount" resultType="java.lang.Integer">select count(*) from user</select></mapper>

controller：

package boc.ljh.controller;import boc.ljh.config.AppCode;
import boc.ljh.config.PaginationHelper;
import boc.ljh.config.Result;
import boc.ljh.pojo.User;
import boc.ljh.service.UserService;
import com.github.xiaoymin.knife4j.annotations.ApiOperationSupport;
import io.swagger.annotations.*;
import org.springframework.web.bind.annotation.*;import javax.annotation.Resource;
import javax.jws.soap.SOAPBinding;@Api(tags = "用户管理")
@RestController
@RequestMapping("/user")
public class UserController {@Resourceprivate UserService userService;@ApiOperation("获取用户列表")@PostMapping("loadAllUserList")@ApiOperationSupport(ignoreParameters = {"data","options","totalSize","totalPages","start"})public Result<PaginationHelper> loadAllUserInfo(@RequestBody PaginationHelper paginationHelper){Result<PaginationHelper> result = new Result();if(paginationHelper == null){paginationHelper = new PaginationHelper<>();}if(paginationHelper.getOptions() == null){paginationHelper.setOptions(new User());}paginationHelper.setData(userService.loadAllUserInfo(paginationHelper));paginationHelper.setTotalSize(userService.loadAllUserCount());result.setDate(paginationHelper);result.setStatus(200);result.setMessage("查询成功");return result;}}

四、测试

重点

首先要知道sql中的limit不是直接分页查询的。比如limit 1,3,。并不是查询第一页每页三条数据的意思，而从第二条数据起查询三条数据，查询的是表中的2-5之间的数据。

select * from user limit 0,5。查询第0-5条之间的数据

select * from user limit 1,5。查询第1-6条之间的数据

select * from user limit 5,5。查询第6-11条之间的数据

可以看封装的分页查询类中有start（开始记录索引）、pageNum（当前页码）、pageSize（每页条数）这个三个参数。
sql需要写成下面这种形式传start（开始记录索引）、pageNum（当前页码）。而不是pageNum（当前页码）、pageSize（每页条数）。

select * from user limit #{start},#{pageSize}

sql不能改变就需要改变其他东西实现页面输入pageNum和pageSize参数实现分页查询功能。

改变封装的分页查询类中start参数的get方法，如下所示：

当页面输入pageNum=1，pageSize=10时，通过下面的改动，上面的sql就会变成
select * from user limit 0,10
当页面输入pageNum=2，pageSize=10时，通过下面的改动，上面的sql就会变成
select * from user limit 10,10
当页面输入pageNum=3，pageSize=10时，通过下面的改动，上面的sql就会变成
select * from user limit 20,10
这样就可以实现分页查询。

 public int getStart() {if(pageNum==0){pageNum=1;}start = this.getPageSize() * (pageNum-1);return start;}