SpringBoot整合MyBatisPlus的PageHelper插件实现分页

SpringBoot整合MyBatisPlus的PageHelper插件

在SpringBoot项目中我们经常需要对查询的数据进行分页，其实我们可以复用查询所有数据的数据层接口，然后借助PageHelper插件对查询的数据进行分页，然后返回给前端

配置

添加POM依赖

<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>
    <parent>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-parentartifactId>
        <version>2.5.1version>
    parent>
    <groupId>com.examplegroupId>
    <artifactId>mongo-adminartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <properties>
        <java.version>1.8java.version>
    properties>
    <dependencies>

        <dependency>
            <groupId>com.examplegroupId>
            <artifactId>mongo-coreartifactId>
            <version>0.0.1-SNAPSHOTversion>
        dependency>

        
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>

        
        <dependency>
            <groupId>com.baomidougroupId>
            <artifactId>mybatis-plus-boot-starterartifactId>
            <version>3.4.1version>
        dependency>

        
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <scope>runtimescope>
        dependency>

        
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-testartifactId>
            <scope>testscope>
        dependency>

        
        <dependency>
            <groupId>org.projectlombokgroupId>
            <artifactId>lombokartifactId>
            <version>1.18.12version>
        dependency>

        
        <dependency>
            <groupId>com.baomidougroupId>
            <artifactId>mybatis-plus-generatorartifactId>
            <version>3.4.1version>
        dependency>

        
        <dependency>
            <groupId>org.apache.velocitygroupId>
            <artifactId>velocity-engine-coreartifactId>
            <version>2.3version>
        dependency>

        
        <dependency>
            <groupId>io.springfoxgroupId>
            <artifactId>springfox-boot-starterartifactId>
            <version>3.0.0version>
        dependency>

        
        <dependency>
            <groupId>com.alibabagroupId>
            <artifactId>druid-spring-boot-starterartifactId>
            <version>1.1.22version>
        dependency>

        <dependency>
            <groupId>log4jgroupId>
            <artifactId>log4jartifactId>
            <version>1.2.17version>
        dependency>

        
        <dependency>
            <groupId>com.github.pagehelpergroupId>
            <artifactId>pagehelper-spring-boot-starterartifactId>
            <version>1.3.0version>
        dependency>

    dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
            plugin>
        plugins>
        <resources>
            <resource>
                <directory>src/main/javadirectory>
                
                <includes>
                    <include>**/*.xmlinclude>
                includes>
            resource>
            
            <resource>
                <directory>src/main/resourcesdirectory>
                <includes>
                    <include>**/*.ymlinclude>
                    <include>**/*.propertiesinclude>
                    <include>**/*.xmlinclude>
                includes>
            resource>
        resources>
    build>


project>

添加YML配置

#默认datasource配置
#spring:
#  datasource:
#    type: com.alibaba.druid.pool.DruidDataSource
#    driver-class-name: com.mysql.cj.jdbc.Driver
#    url: jdbc:mysql://localhost:3306/mongo?serverTimezone=UTC
#    username: root
#    password: root


#整合Druid连接池的datasource配置
spring:
  datasource:
    username: root
    password: root
    url: jdbc:mysql://localhost:3306/mongo?characterEncoding=utf-8&serverTimezone=UTC
    driver-class-name: com.mysql.cj.jdbc.Driver
    type: com.alibaba.druid.pool.DruidDataSource
    initial-size: 5
    min-idle: 5
    max-active: 20
    max-wait: 60000
    test-while-idle: true
    time-between-eviction-runs-millis: 60000
    min-evictable-idle-time-millis: 30000
    validation-query: select 'x'
    test-on-borrow: false
    test-on-return: false
    pool-prepared-statements: true
    filters: stat,wall,slf4j
    max-pool-prepared-statement-per-connection-size: 20
    use-global-data-source-stat: true
    connect-properties: druid.stat.mergeSql=true;druid.stat.slowSqlMillis=5000


#服务端口
server:
  port: 80


#PageHelper配置
pagehelper:
  helper-dialect: mysql
  reasonable: true
  support-methods-arguments: true


#Spring整合MP
mybatis-plus:
  #定义别名包
  type-aliases-package: com.example.mongoadmin.entity
  #导入映射文件
  mapper-locations: classpath:/mapper/*.xml
  #开启驼峰映射
  configuration:
    map-underscore-to-camel-case: true


#为com.example.mongoadmin.mapper包下的SQL执行打印日志
logging:
  level:
    com.example.mongoadmin.mapper: info

编写代码

因为我们可以复用查询全部的数据层代码，即Mapper代码，然后使用PageHelper去做分页，所以我们只需要在Service层实现一个分页查询的服务即可

Service

接口

package com.example.mongoadmin.service;

import com.example.mongoadmin.entity.User;
import com.baomidou.mybatisplus.extension.service.IService;
import com.github.pagehelper.PageInfo;

import java.util.List;

/**
 * 

 * 用户管理 服务类
 * 
 *
 * @author ZJ
 * @since 2023-06-24
 */
public interface IUserService extends IService<User> {

    List<User> findAll();

    PageInfo findByPage(int pageNum, int pageSize);

}

具体实现

package com.example.mongoadmin.service.impl;

import com.example.mongoadmin.entity.User;
import com.example.mongoadmin.mapper.UserMapper;
import com.example.mongoadmin.service.IUserService;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;
import java.util.List;

/**
 * 

 * 用户管理 服务实现类
 * 
 *
 * @author ZJ
 * @since 2023-06-24
 */
@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements IUserService {

    @Resource
    private UserMapper userMapper;

    @Override
    public List<User> findAll() {
        return userMapper.findAll();
    }

    @Override
    public PageInfo findByPage(int pageNum, int pageSize) {
        PageHelper.startPage(pageNum, pageSize);
        List<User> all = userMapper.findAll();
        PageInfo<User> pageInfo = new PageInfo<User>(all);
        return pageInfo;
    }

}

说明：我们使用PageHelper.startPage进行分页，然后调用userMapper.findAll()查询分页数据，最后使用PageInfo封装数据返回

Controller

前端通过访问/user/findByPage接口并传递分页参数访问服务

package com.example.mongoadmin.controller;

import com.example.mongoadmin.entity.User;
import com.example.mongoadmin.service.IUserService;
import com.github.pagehelper.PageInfo;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

import javax.annotation.Resource;
import java.util.List;

/**
 * 

 * 用户管理 前端控制器
 * 
 *
 * @author ZJ
 * @since 2023-06-24
 */
@RestController
@RequestMapping("/user")
public class UserController {

    @Resource
    private IUserService userService;

    @GetMapping("/findAll")
    public List<User> findAll() {
        return userService.findAll();
    }

    @GetMapping("/findByPage")
    public PageInfo findByPage(int pageNum, int pageSize) {
        return userService.findByPage(pageNum, pageSize);
    }

}

验证

使用ApiFox调用分页接口，查询第1页的5条数据

可以看到，后端也只是查到了5条数据，这其实是PageHelper在findAll方法的SQL调用前给它拼接了limit条件，所以只返回了我们需要的数据，而不是全部数据