Spring Boot 整合 MyBatis 连接数据库及常见问题_Java

mybatis 是一个优秀的持久层框架，支持定制化 sql、存储过程以及高级映射。下面详细介绍如何在 spring boot 项目中整合 mybatis 并连接数据库。

一、基本配置

1. 添加依赖

在pom.xml中添加以下依赖：

<!-- spring boot starter web -->
<dependency>
    <groupid>org.springframework.boot</groupid>
    <artifactid>spring-boot-starter-web</artifactid>
</dependency>
<!-- mybatis spring boot starter -->
<dependency>
    <groupid>org.mybatis.spring.boot</groupid>
    <artifactid>mybatis-spring-boot-starter</artifactid>
    <version>2.2.0</version> <!-- 使用最新版本 -->
</dependency>
<!-- 数据库驱动，根据你的数据库选择 -->
<dependency>
    <groupid>mysql</groupid>
    <artifactid>mysql-connector-java</artifactid>
    <scope>runtime</scope>
</dependency>
<!-- 其他可能需要的依赖 -->
<dependency>
    <groupid>com.alibaba</groupid>
    <artifactid>druid-spring-boot-starter</artifactid>
    <version>1.2.6</version> <!-- druid 连接池 -->
</dependency>

2. 配置数据库连接

在application.yml或application.properties中配置数据库连接：

# application.yml 配置示例
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/your_database?usessl=false&servertimezone=utc&characterencoding=utf8
    username: your_username
    password: your_password
    driver-class-name: com.mysql.cj.jdbc.driver
    type: com.alibaba.druid.pool.druiddatasource # 使用druid连接池
# mybatis 配置
mybatis:
  mapper-locations: classpath:mapper/*.xml  # mapper.xml文件位置
  type-aliases-package: com.example.model   # 实体类所在包
  configuration:
    map-underscore-to-camel-case: true      # 开启驼峰命名转换

二、项目结构

典型的项目结构如下：

src/main/java
└── com.example.demo
    ├── demoapplication.java          # 启动类
    ├── config
    │   └── mybatisconfig.java        # mybatis配置类(可选)
    ├── controller
    │   └── usercontroller.java       # 控制器
    ├── service
    │   ├── userservice.java          # 服务接口
    │   └── impl
    │       └── userserviceimpl.java  # 服务实现
    ├── mapper
    │   └── usermapper.java           # mapper接口
    └── model
        └── user.java                 # 实体类
src/main/resources
├── application.yml                   # 配置文件
└── mapper
    └── usermapper.xml                # sql映射文件

三、核心组件实现（示例）

1. 实体类

package com.example.model;
public class user {
    private long id;
    private string username;
    private string password;
    private string email;
    // getters and setters
    // tostring()
}

2. mapper 接口

package com.example.mapper;
import com.example.model.user;
import org.apache.ibatis.annotations.*;
import java.util.list;
@mapper // 重要：标识这是一个mybatis的mapper接口
public interface usermapper {
    @select("select * from user where id = #{id}")
    user findbyid(long id);
    @insert("insert into user(username, password, email) values(#{username}, #{password}, #{email})")
    @options(usegeneratedkeys = true, keyproperty = "id")
    int insert(user user);
    @update("update user set username=#{username}, password=#{password}, email=#{email} where id=#{id}")
    int update(user user);
    @delete("delete from user where id=#{id}")
    int delete(long id);
    // xml配置方式
    list<user> findall();
}

3. mapper xml 文件

src/main/resources/mapper/usermapper.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="com.example.mapper.usermapper">
    <resultmap id="userresultmap" type="user">
        <id property="id" column="id"/>
        <result property="username" column="username"/>
        <result property="password" column="password"/>
        <result property="email" column="email"/>
    </resultmap>
    <select id="findall" resultmap="userresultmap">
        select * from user
    </select>
</mapper>

4. service 层

package com.example.service;
import com.example.model.user;
import java.util.list;
public interface userservice {
    user findbyid(long id);
    list<user> findall();
    int save(user user);
    int update(user user);
    int delete(long id);
}

service层实现类：

package com.example.service.impl;
import com.example.mapper.usermapper;
import com.example.model.user;
import com.example.service.userservice;
import org.springframework.beans.factory.annotation.autowired;
import org.springframework.stereotype.service;
import java.util.list;
@service
public class userserviceimpl implements userservice {
    @autowired
    private usermapper usermapper;
    @override
    public user findbyid(long id) {
        return usermapper.findbyid(id);
    }
    @override
    public list<user> findall() {
        return usermapper.findall();
    }
    @override
    public int save(user user) {
        return usermapper.insert(user);
    }
    @override
    public int update(user user) {
        return usermapper.update(user);
    }
    @override
    public int delete(long id) {
        return usermapper.delete(id);
    }
}

5. controller 层：

package com.example.controller;
import com.example.model.user;
import com.example.service.userservice;
import org.springframework.beans.factory.annotation.autowired;
import org.springframework.web.bind.annotation.*;
import java.util.list;
@restcontroller
@requestmapping("/users")
public class usercontroller {
    @autowired
    private userservice userservice;
    @getmapping("/{id}")
    public user getuser(@pathvariable long id) {
        return userservice.findbyid(id);
    }
    @getmapping
    public list<user> getallusers() {
        return userservice.findall();
    }
    @postmapping
    public int createuser(@requestbody user user) {
        return userservice.save(user);
    }
    @putmapping
    public int updateuser(@requestbody user user) {
        return userservice.update(user);
    }
    @deletemapping("/{id}")
    public int deleteuser(@pathvariable long id) {
        return userservice.delete(id);
    }
}

四、高级特性

1. 动态sql

在xml中使用动态sql：

<select id="findbycondition" parametertype="map" resultmap="userresultmap">
    select * from user
    <where>
        <if test="username != null and username != ''">
            and username like concat('%', #{username}, '%')
        </if>
        <if test="email != null and email != ''">
            and email = #{email}
        </if>
    </where>
</select>

2. 分页查询

使用pagehelper插件：

添加依赖：

<select id="findbycondition" parametertype="map" resultmap="userresultmap">
    select * from user
    <where>
        <if test="username != null and username != ''">
            and username like concat('%', #{username}, '%')
        </if>
        <if test="email != null and email != ''">
            and email = #{email}
        </if>
    </where>
</select>

使用示例：

<dependency>
    <groupid>com.github.pagehelper</groupid>
    <artifactid>pagehelper-spring-boot-starter</artifactid>
    <version>1.4.1</version>
</dependency>

3. 多数据源配置

配置多个数据源：

spring:
  datasource:
    primary:
      url: jdbc:mysql://localhost:3306/db1
      username: root
      password: root
      driver-class-name: com.mysql.cj.jdbc.driver
    secondary:
      url: jdbc:mysql://localhost:3306/db2
      username: root
      password: root
      driver-class-name: com.mysql.cj.jdbc.driver

创建配置类：

@configuration
@mapperscan(basepackages = "com.example.mapper.primary", sqlsessionfactoryref = "primarysqlsessionfactory")
public class primarydatasourceconfig {
    @bean(name = "primarydatasource")
    @configurationproperties(prefix = "spring.datasource.primary")
    public datasource primarydatasource() {
        return datasourcebuilder.create().build();
    }
    @bean(name = "primarysqlsessionfactory")
    public sqlsessionfactory primarysqlsessionfactory(@qualifier("primarydatasource") datasource datasource) throws exception {
        sqlsessionfactorybean bean = new sqlsessionfactorybean();
        bean.setdatasource(datasource);
        bean.setmapperlocations(new pathmatchingresourcepatternresolver().getresources("classpath:mapper/primary/*.xml"));
        return bean.getobject();
    }
    @bean(name = "primarytransactionmanager")
    public datasourcetransactionmanager primarytransactionmanager(@qualifier("primarydatasource") datasource datasource) {
        return new datasourcetransactionmanager(datasource);
    }
}
// 类似地创建secondarydatasourceconfig

五、常见问题解决

mapper接口无法注入：

确保启动类上有@mapperscan("com.example.mapper")注解
或者每个mapper接口上有@mapper注解

xml文件找不到：

检查mybatis.mapper-locations配置是否正确
确保xml文件在resources目录下正确位置

驼峰命名不生效：

确认配置mybatis.configuration.map-underscore-to-camel-case=true

连接池配置：

推荐使用druid连接池，并配置合理的连接参数

事务管理：

在service方法上添加@transactional注解

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Spring Boot 整合 MyBatis 连接数据库及常见问题

2025年03月27日 • Java •我要评论