Spring整合MyBatis详细教程

亦凉 2022-09-05 11:29 156阅读 0赞

# 1. 为什么需要Spring？Spring可以带来哪些变化？ #

### 将对象创建这个过程交给Spring（IOC），不再需要硬编码在程序中，配置xml文件或注解即可；另外Spirng还提供了数据库的事务管理、日志等功能（AOP）。最直观的变化就是：可以不再使用MyBatis配置文件以及不用再手动new SqlSessionFactory、SqlSession等对象 ###

# 2. 回顾MyBatis #

首先来回顾在MyBatis中如何操作数据库。以操作的数据库名为mybatis，表名employee为例，employee表中拥有字段id、lastName、gender、email

## 2.1 创建表对应的POJO(Bean) ##

package com.domain;
    public class Employee {
        
        private Integer id;
        private String lastName;
        private String gender;
        private String email;
        public Employee() {
        
        }
        public Employee(Integer id, String lastName, String gender, String email) {
        
            this.id = id;
            this.lastName = lastName;
            this.gender = gender;
            this.email = email;
        }
        ......get set方法省略

## 2.2 创建接口DAO ##

package com.dao;
    public interface EmployeeDao {
        
    	//以通过id查employee为例
        public Employee getEmployeeById(Integer id);
    }

## 2.3 创建DAO的映射文件 ##

EmployeeMapper.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.dao.EmployeeDao">
        <select id="getEmployeeById" resultType="com.domain.Employee">
            select * from Employee where id=#{id}
        </select>
    </mapper>

## 2.4 编写Service层 ##

EmployeeService接口：

package com.service;
    import com.domain.Employee;
    public interface EmployeeService {
        
        Employee getEmployeeById(Integer id);
    }

EmployeeServiceImpl实现类：

public class EmployeeServiceImpl implements EmployeeService {
        
        static InputStream inputStream=null;
        static {
        
            String resource = "config.xml";
            try {
        
                inputStream = Resources.getResourceAsStream(resource);
            } catch (IOException e) {
        
                e.printStackTrace();
            }
        }
       	//1.读取全局xml配置文件，创建SqlSessionFactory对象
        private final SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
        
        @Override
        public Employee getEmployeeById(Integer id) {
        
        	//2.通过创建SqlSessionFactory对象获取SqlSession对象
            SqlSession sqlSession = sqlSessionFactory.openSession();
            //3.通过SqlSession对象获取代理对象mapper，传入接口class对象,
            EmployeeDao mapper = sqlSession.getMapper(EmployeeDao.class);
            //4.通过mapper调用接口对应方法
            return  mapper.queryEmployeeById(id);
        }

## 2.5创建MyBatis配置文件 ##

config.xml：

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration
            PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
            "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                    <property name="username" value="root"/>
                    <property name="password" value="123456"/>
                </dataSource>
            </environment>
        </environments>
        
        <mappers>
            <mapper resource="EmployeeMapper.xml"/>
        </mappers>
    </configuration>

## 2.6 开始测试 ##

@Test
    public void testImpl()
    {
        
        EmployeeService employeeService=new EmployeeServiceImpl();
        Employee employeeById = employeeService.getEmployeeById(6);
        System.out.println(employeeById);
    }

至此就完成了通过MyBatis访问数据库的一系列操作，**在这里我们主要关注2.4与2.5中的操作，联系后面的讲解，将会深入体会到引入Spring后带来哪些便捷**。另外根据上面的代码，我们将MyBatis运行时需要创建的对象抽离出一张流程图，如下  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzMzNTM5Mg_size_16_color_FFFFFF_t_70]

--------------------

# 3.将MyBatis与Spring整合 #

**在完成前面2.1(POJO)、2.2(DAO接口)、2.3(mapper映射文件)三个步骤的基础之上**：

## 3.1 使用Maven导入相关依赖 ##

<dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>
    
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.25</version>
        </dependency>
        
    
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.3.9</version>
        </dependency>
        
    
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-spring</artifactId>
            <version>2.0.2</version>
        </dependency>
    </dependencies>

## 3.2 编写Spring管理MyBatis的xml（核心） ##

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:context="http://www.springframework.org/schema/context"
        xsi:schemaLocation="http://www.springframework.org/schema/beans
            https://www.springframework.org/schema/beans/spring-beans.xsd
            http://www.springframework.org/schema/context
            https://www.springframework.org/schema/context/spring-context.xsd">
        <context:annotation-config/>
        
        ！！使用Spring配置dataSource 相当于MyBatis配置文件的<environments>！！
        <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
            <property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/>
            <property name="url" value="jdbc:mysql://localhost:3306/book"/>
            <property name="username" value="root"/>
            <property name="password" value="123456"/>
        </bean>
        
         ！！配置SqlSessionFactoryBean 等同于SqlSessionFactory 做读取数据源以及注册mapper.xml的工作
        <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
            <property name="dataSource" ref="dataSource"/>引用上面的dataSource
            <property name="mapperLocations" value="classpath:EmployeeMapper.xml"/>
        </bean>
        ！！获得Mapper代理对象 等同于getMapper()
        <bean id="employeeMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
            <property name="mapperInterface" value="com.lin.mapper.EmployeeMapper" />
            <property name="sqlSessionFactory" ref="sqlSessionFactory" />
        </bean>
        ！！注册employeeServiceImpl
        <bean id="employeeServiceImpl" class="com.lin.service.EmployeeServiceImpl"/>
    
    </beans>

## 3.3 重新编写Service层 ##

package com.lin.service;
    import com.lin.mapper.EmployeeMapper;
    import com.lin.pojo.Employee;
    import org.springframework.beans.factory.annotation.Autowired;
    public class EmployeeServiceImpl implements EmployeeService {
        
        private EmployeeMapper employeeMapper;
        
        @Autowired //构造器注入 注入的就是id="employeeMapper"这个bean
        public EmployeeServiceImpl(EmployeeMapper employeeMapper) {
        
            this.employeeMapper = employeeMapper;
        }
        
        @Override
        public Employee getEmployeeById(Integer id) {
        
            return employeeMapper.queryEmployeeById(id);
        }
    }

## 3.4 测试 ##

@Test
    public void testImpl()
    {
        
    	ApplicationContext context=new ClassPathXmlApplicationContext("Spring-mapper.xml");
        EmployeeService employeeServiceImpl = context.getBean("employeeServiceImpl", EmployeeService.class);
        Employee employee = employeeServiceImpl.getEmployeeById(6);
        System.out.println(employee);
    }

# 4. 总结 #

## 其实在Spring中使用MyBatis的原理是一样的，只不过Spring将其封装了，并且以bean的方式注入，从而省去了创建对象的过程，使得代码更加整洁，更易维护。通过对比Spring-mybatis源码，可以总结出下图 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzMzNTM5Mg_size_16_color_FFFFFF_t_70 1]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzMzNTM5Mg_size_16_color_FFFFFF_t_70]: /images/20220829/b0ab3da183724fc8aa585d3957bb5a82.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzMzNTM5Mg_size_16_color_FFFFFF_t_70 1]: /images/20220829/85dabe9f205d427fa5b6a7d4eaf6078e.png