1. Navicat查询数据

• Navicat中查询所有数据

SELECT * FROM sys_user;

• Navicat中查询前两条数据（俩种方式）

SELECT * FROM sys_user LIMIT 2;
//从0开始，第一个参数是起始位置即(pageNum-1)*pageSize，第二个参数是步长
SELECT * FROM sys_user LIMIT 0,2; 

2. 分页查询最主要的就是对pageNum的处理

3. 操作：

1. 传入pageNum、pageSize，并使用postman测试成功与否。

//UserController.java传入pageNum、pageSize
@GetMapping("/page")public Map<String,Object> findPage(@RequestParam Integer pageNum, @RequestParam Integer pageSize) {pageNum = (pageNum - 1) * pageSize;return (Map<String, Object>) userMapper.selectPage(pageNum,pageSize);

//UserMapper.java传入pageNum、pageSize
@Select("select * from sys_user limit #{pageNum}, #{pageSize}")List<User> selectPage(@Param("pageNum") Integer pageNum, @Param("pageSize") Integer pageSize);

2. 使用findAll接口查询总条数
   UserController.java写一个新方法selectPage查询总条数，封装一个结果参数Map并返回。

   public Map<String,Object> findPage(@RequestParam Integer pageNum,@RequestParam Integer pageSize) {pageNum = (pageNum - 1) * pageSize;List<User> data = userMapper.selectPage(pageNum,pageSize);Integer total = userMapper.seleceTotal();Map<String,Object> res = new HashMap<>();res.put("data",data);res.put("total",total);return res;}

3. 结合前端页面查看需要绑定的数据
   分页数据total和表格数据data要相关联
   3.1 前后关联Home.vue添加create函数

created(){//请求分页查询数据this.load()
},load(){fetch("http://localhost:9090/user/page?pageNum="+this.pageNum+"&pageSize=" + this.pageSize).then(res => res.json()).then(res =>  {console.log(res)this.tableData = res.datathis.total = res.total})
},

4. 前端报错，这是因为不同端口请求数据出现了跨域
   解决方法：后端设置跨域。
   新建包config–>new一个java class–>添加代码(包名不用粘贴)
   

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.UrlBasedCorsConfigurationSource;
import org.springframework.web.filter.CorsFilter;@Configuration
public class CorsConfig {// 当前跨域请求最大有效时长。这里默认1天private static final long MAX_AGE = 24 * 60 * 60;@Beanpublic CorsFilter corsFilter() {UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();CorsConfiguration corsConfiguration = new CorsConfiguration();corsConfiguration.addAllowedOrigin("http://localhost:8080"); // 1 设置访问源地址corsConfiguration.addAllowedHeader("*"); // 2 设置访问源请求头corsConfiguration.addAllowedMethod("*"); // 3 设置访问源请求方法corsConfiguration.setMaxAge(MAX_AGE);source.registerCorsConfiguration("/**", corsConfiguration); // 4 对接口配置跨域设置return new CorsFilter(source);}
}

5. 数据有了，改表格渲染
   

<el-table :data="tableData" border stripe :header-cell-class-name="headerBg"><el-table-column prop="id" label="ID" width="80"></el-table-column><el-table-column prop="username" label="用户名" width="140"></el-table-column><el-table-column prop="nickname" label="昵称" width="120"></el-table-column><el-table-column prop="email" label="邮箱"></el-table-column><el-table-column prop="phone" label="电话" width="120"></el-table-column><el-table-column prop="address" label="地址" width="120"></el-table-column>

6. 拼接绑定前端传来的pageNum、pageSize 及后端数据请求完后的total
7. 关键一步：触发
   

@size-change="handleSizeChange" 
@current-change="handleCurrentChange"

 load(){fetch("http://localhost:9090/user/page?pageNum="+this.pageNum+"&pageSize=" + this.pageSize + "&username=" + this.username).then(res => res.json()).then(res =>  {console.log(res)this.tableData = res.datathis.total = res.total})},handleSizeChange(pageSize){console.log(pageSize)this.pageSize = pageSizethis.load()},handleCurrentChange(pageNum){console.log(pageNum)this.pageNum = pageNumthis.load()}

---

修改后的各部分

UserMapper.java

package com.qingge.springboot.mapper;import com.qingge.springboot.entity.User;
import org.apache.ibatis.annotations.*;import java.util.List;@Mapper
public interface UserMapper {@Select("SELECT * from sys_user")List<User> findAll();@Insert("INSERT into sys_user(username, password,nickname,email,phone,address) VALUES (#{username}, #{password}," +" #{nickname}, #{email},#{phone}, #{address})")int insert(User user);int update(User user);@Delete("delete from sys_user where id = #{id}")Integer deleteById(@Param("id") Integer id);@Select("select * from sys_user where username like #{username} limit #{pageNum}, #{pageSize}")List<User> selectPage(@Param("pageNum") Integer pageNum, @Param("pageSize") Integer pageSize, @Param("username") String username);@Select("select count(*) from sys_user where username like concat('%',#{username},'%')")Integer seleceTotal(String username);
}

UserController.java

package com.qingge.springboot.controller;import com.qingge.springboot.entity.User;
import com.qingge.springboot.mapper.UserMapper;
import com.qingge.springboot.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;import java.util.HashMap;
import java.util.List;
import java.util.Map;@RestController
@RequestMapping("/user")
public class UserController {@Autowiredprivate UserMapper userMapper;@Autowiredprivate UserService userService;// 新增和修改@PostMappingpublic Integer save(@RequestBody User user) {// 新增或者更新return userService.save(user);}// 查询所有数据@GetMappingpublic List<User> findall() {List<User> all = userMapper.findAll();return all;}@DeleteMapping("/{id}")public Integer delete(@PathVariable Integer id) {return userMapper.deleteById(id);}// 分页查询//  接口路径：/user/page?pageNum=1&pageSize=10// @RequestParam接受// limit第一个参数 = (pageNum - 1) * pageSize// pageSize@GetMapping("/page")public Map<String,Object> findPage(@RequestParam Integer pageNum,@RequestParam Integer pageSize,@RequestParam String username) {pageNum = (pageNum - 1) * pageSize;username = "%" + username + "%";List<User> data = userMapper.selectPage(pageNum,pageSize,username);Integer total = userMapper.seleceTotal(username);Map<String,Object> res = new HashMap<>();res.put("data",data);res.put("total",total);return res;}
}

User.java

package com.qingge.springboot.entity;import com.fasterxml.jackson.annotation.JsonIgnore;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;@Data
public class User {private Integer id;private String username;@JsonIgnoreprivate String password;private String nickname;private String email;private String phone;private String address;}

CorsConfig.java

package com.qingge.springboot.config;import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.UrlBasedCorsConfigurationSource;
import org.springframework.web.filter.CorsFilter;@Configuration
public class CorsConfig {// 当前跨域请求最大有效时长。这里默认1天private static final long MAX_AGE = 24 * 60 * 60;@Beanpublic CorsFilter corsFilter() {UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();CorsConfiguration corsConfiguration = new CorsConfiguration();corsConfiguration.addAllowedOrigin("http://localhost:8080"); // 1 设置访问源地址corsConfiguration.addAllowedHeader("*"); // 2 设置访问源请求头corsConfiguration.addAllowedMethod("*"); // 3 设置访问源请求方法corsConfiguration.setMaxAge(MAX_AGE);source.registerCorsConfiguration("/**", corsConfiguration); // 4 对接口配置跨域设置return new CorsFilter(source);}
}

HomeView.vue

<template><el-container style="min-height: 100vh"><el-aside :width="sideWidth + 'px'" style="box-shadow: 2px 0 6px rgb(0 21 41 );"><el-menu :default-openeds="['1', '3']" style="min-height: 100%; overflow-x: hidden"background-color="rgb(48, 65, 86)"text-color="#fff"active-text-color="#ffd04b":collapse-transition="false":collapse="isCollapse"><div style="height: 60px; line-height: 60px; text-align: center"><img src="../assets/logo.png" alt="" style="width: 20px; position: relative; top: 5px; right: 5px"><b style="color: white" v-show="logoTextShow">后台管理系统</b></div><el-submenu index="1"><template slot="title"><i class="el-icon-message"></i><span slot="title">导航一</span></template><el-menu-item-group title="分组2"><el-menu-item index="1-3">选项3</el-menu-item></el-menu-item-group><el-submenu index="1-4"><template slot="title">选项4</template><el-menu-item index="1-4-1">选项4-1</el-menu-item></el-submenu></el-submenu><el-submenu index="2"><template slot="title"><i class="el-icon-menu"></i><span slot="title">导航二</span></template><el-submenu index="2-4"><template slot="title">选项4</template><el-menu-item index="2-4-1">选项4-1</el-menu-item></el-submenu></el-submenu><el-submenu index="3"><template slot="title"><i class="el-icon-setting"></i><span slot="title">导航三</span></template><el-submenu index="3-4"><template slot="title">选项4</template><el-menu-item index="3-4-1">选项4-1</el-menu-item></el-submenu></el-submenu></el-menu></el-aside><el-container><el-header style="font-size: 12px; border-bottom: 1px solid #ccc; line-height: 60px; display: flex"><div style="flex: 1; font-size: 20px"><span :class="collapseBtnClass" style="cursor: pointer" @click="collapse"></span></div><el-dropdown style="width: 70px; cursor: pointer"><span>王小虎</span><i class="el-icon-arrow-down" style="margin-left: 5px"></i><el-dropdown-menu slot="dropdown" ><el-dropdown-item style="font-size: 14px; padding: 5px 0">个人信息</el-dropdown-item><el-dropdown-item style="font-size: 14px; padding: 5px 0">退出</el-dropdown-item></el-dropdown-menu></el-dropdown></el-header><el-main><div style="margin-bottom: 30px"><el-breadcrumb separator="/"><el-breadcrumb-item :to="{ path: '/' }">首页</el-breadcrumb-item><el-breadcrumb-item>用户管理</el-breadcrumb-item></el-breadcrumb></div><div style="margin: 10px 0"><el-input style="width: 200px" placeholder="请输入名称" suffix-icon="el-icon-search" v-model="username"></el-input>
<!--          <el-input style="width: 200px" placeholder="请输入邮箱" suffix-icon="el-icon-message" class="ml-5"></el-input>-->
<!--          <el-input style="width: 200px" placeholder="请输入地址" suffix-icon="el-icon-position" class="ml-5"></el-input>--><el-button class="ml-5" type="primary" @click="load">搜索</el-button></div><div style="margin: 10px 0"><el-button type="primary">新增 <i class="el-icon-circle-plus-outline"></i></el-button><el-button type="danger">批量删除 <i class="el-icon-remove-outline"></i></el-button><el-button type="primary">导入 <i class="el-icon-bottom"></i></el-button><el-button type="primary">导出 <i class="el-icon-top"></i></el-button></div><el-table :data="tableData" border stripe :header-cell-class-name="headerBg"><el-table-column prop="id" label="ID" width="80"></el-table-column><el-table-column prop="username" label="用户名" width="140"></el-table-column><el-table-column prop="nickname" label="昵称" width="120"></el-table-column><el-table-column prop="email" label="邮箱"></el-table-column><el-table-column prop="phone" label="电话" width="120"></el-table-column><el-table-column prop="address" label="地址" width="120"></el-table-column><el-table-column label="操作"  width="200" align="center"><template slot-scope="scope"><el-button type="success">编辑 <i class="el-icon-edit"></i></el-button><el-button type="danger">删除 <i class="el-icon-remove-outline"></i></el-button></template></el-table-column></el-table><div style="padding: 10px 0"><el-pagination@size-change="handleSizeChange"@current-change="handleCurrentChange":current-page="pageNum":page-sizes="[2, 5, 10, 20]":page-size="pageSize"layout="total, sizes, prev, pager, next, jumper":total="total"></el-pagination></div></el-main></el-container></el-container>
</template><script>export default {name: 'Home',data() {return {tableData: [],total: 0,pageNum:1,pageSize:2,username:"",msg: "hello 青哥哥",collapseBtnClass: 'el-icon-s-fold',isCollapse: false,sideWidth: 200,logoTextShow: true,headerBg: 'headerBg'}},created(){//请求分页查询数据this.load()},methods: {collapse() {  // 点击收缩按钮触发this.isCollapse = !this.isCollapseif (this.isCollapse) {  // 收缩this.sideWidth = 64this.collapseBtnClass = 'el-icon-s-unfold'this.logoTextShow = false} else {   // 展开this.sideWidth = 200this.collapseBtnClass = 'el-icon-s-fold'this.logoTextShow = true}},load(){fetch("http://localhost:9090/user/page?pageNum="+this.pageNum+"&pageSize=" + this.pageSize + "&username=" + this.username).then(res => res.json()).then(res =>  {console.log(res)this.tableData = res.datathis.total = res.total})},handleSizeChange(pageSize){console.log(pageSize)this.pageSize = pageSizethis.load()},handleCurrentChange(pageNum){console.log(pageNum)this.pageNum = pageNumthis.load()}}
}
</script><style>
.headerBg {background: #eee!important;
}
</style>