序言

springboot + mybatis-plus + druid 是如今非常好用一套组合方案，可以大大提升我们开发的效率。

本文记录一下老马自己的实战使用笔记，希望给你的工作和学习提供一点帮助。

springboot 整合 mybatis-plus

maven 依赖

版本

<mybatis.version>3.4.4</mybatis.version>
<mybatis-spring.version>1.3.1</mybatis-spring.version>
<mybatis-plus.version>2.3</mybatis-plus.version>
<java.version>1.8</java.version>
<mysql.version>5.1.47</mysql.version>
<druid.version>1.1.14</druid.version>
<aspectj.version>1.8.10</aspectj.version>
<velocity.version>2.0</velocity.version>
<spring-boot.version>1.5.11.RELEASE</spring-boot.version>

依赖

<!-- mybatis-plus-->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>${mybatis.version}</version>
</dependency>
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis-spring</artifactId>
    <version>${mybatis-spring.version}</version>
</dependency>
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus</artifactId>
    <version>${mybatis-plus.version}</version>
    <exclusions>
        <exclusion>
            <artifactId>mybatis</artifactId>
            <groupId>org.mybatis</groupId>
        </exclusion>
        <exclusion>
            <artifactId>mybatis-spring</artifactId>
            <groupId>org.mybatis</groupId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>${mybatis-plus.version}</version>
</dependency>
<!-- mybatis-plus自动化工具需要的依赖 模板-->
<dependency>
    <groupId>org.apache.velocity</groupId>
    <artifactId>velocity-engine-core</artifactId>
    <version>${velocity.version}</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>${mysql.version}</version>
    <scope>runtime</scope>
</dependency>
<!-- alibaba的druid数据库连接池 -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid-spring-boot-starter</artifactId>
    <version>${druid.version}</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jdbc</artifactId>
    <version>${spring-boot.version}</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <version>${spring-boot.version}</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <version>${spring-boot.version}</version>
</dependency>

配置文件

server:
  port: 8080

spring:
  datasource:
    druid:
      username: root
      password: 123456
      url: jdbc:mysql://localhost:3306/padmin?useUnicode=true&characterEncoding=utf-8&useSSL=true&serverTimezone=UTC
      driver-class-name: com.mysql.jdbc.Driver

mybatis-plus:
  mapper-locations: classpath*:com/github/houbb/privilege/admin/dal/mapper/*Mapper.xml
  type-aliases-package: com.github.houbb.privilege.admin.dal.entity

到这里，最基本的配置就完成了。

实现原理，就是通过 springboot-starter 实现的。

分页

如果我们希望使用分页插件，那么配置一下：

import com.baomidou.mybatisplus.plugins.PaginationInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@MapperScan(basePackages = "com.github.houbb.privilege.admin.dal.mapper")
public class DataSourceConfig {

    @Bean
    public PaginationInterceptor paginationInterceptor(){
        PaginationInterceptor page = new PaginationInterceptor();
        //设置方言类型
        page.setDialectType("mysql");
        return page;
    }

}

分页测试

正常情况

public BasePageInfo<User> pageQueryList(CommonPageReq pageReq) {
    Wrapper<User> userWrapper = new EntityWrapper<>();
    
    // 分页查询
    Page<User> userPage = new Page<>(pageReq.getPageNum(), pageReq.getPageSize());
    userPage = this.selectPage(userPage, userWrapper);
    BasePageInfo<User> pageInfo = new BasePageInfo<>();
    pageInfo.setList(userPage.getRecords());
    pageInfo.setTotal(userPage.getTotal());
    return pageInfo;
}

发现这种分页信息是正常的。

不生效的情况

import com.baomidou.mybatisplus.mapper.EntityWrapper;
import com.baomidou.mybatisplus.mapper.Wrapper;
import com.baomidou.mybatisplus.plugins.pagination.PageHelper;
import com.github.houbb.heaven.util.lang.StringUtil;
import com.github.houbb.privilege.admin.common.dto.BasePageInfo;
import com.github.houbb.privilege.admin.common.dto.common.CommonPageReq;
import com.github.houbb.privilege.admin.dal.entity.Role;
import com.github.houbb.privilege.admin.dal.mapper.RoleMapper;
import com.github.houbb.privilege.admin.service.service.RoleService;
import com.baomidou.mybatisplus.service.impl.ServiceImpl;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class RoleServiceImpl extends ServiceImpl<RoleMapper, Role> implements RoleService {

    @Override
    public BasePageInfo<Role> pageQueryList(CommonPageReq pageReq) {
        PageHelper.startPage(pageReq.getPageNum(), pageReq.getPageSize());

        Wrapper<Role> roleWrapper = new EntityWrapper<>();

        List<Role> userList = baseMapper.selectList(roleWrapper);
        long total = PageHelper.getTotal();

        BasePageInfo<Role> pageInfo = new BasePageInfo<>();
        pageInfo.setList(userList);
        pageInfo.setTotal(total);
        return pageInfo;
    }

}

一开始以为是 PageHelper.startPage 后面不是紧跟查询方法，后来调整顺序发现也不行。

问题原因

然后 debug 了一下源码。

mybatis-plus 的 PaginationInterceptor 类

// 先判断是不是SELECT操作
MappedStatement mappedStatement = (MappedStatement) metaObject.getValue("delegate.mappedStatement");
if (!SqlCommandType.SELECT.equals(mappedStatement.getSqlCommandType())) {
    return invocation.proceed();
}
RowBounds rowBounds = (RowBounds) metaObject.getValue("delegate.rowBounds");
/* 不需要分页的场合 */
if (rowBounds == null || rowBounds == RowBounds.DEFAULT) {
    // 本地线程分页
    if (localPage) {
        // 采用ThreadLocal变量处理的分页
        rowBounds = PageHelper.getPagination();
        if (rowBounds == null) {
            return invocation.proceed();
        }
    } else {
        // 无需分页
        return invocation.proceed();
    }
}

发现属性 localPage 没有启动，于是调整一下分页的配置：

@Bean
public PaginationInterceptor paginationInterceptor(){
    PaginationInterceptor page = new PaginationInterceptor();
    //设置方言类型
    page.setDialectType("mysql");
    page.setLocalPage(true);
    return page;
}