Mybatis框架 -- 输入输出参数及配置文件解释

墨蓝 2021-12-22 05:41 180阅读 0赞

#### 一、Mybatis框架的CRUD操作 ####

**1. 创建项目 配置依赖(pom.xml)**

<?xml version="1.0" encoding="UTF-8"?>
    <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
        <parent>
            <artifactId>mybatis01</artifactId>
            <groupId>com.zz</groupId>
            <version>1.0-SNAPSHOT</version>
        </parent>
        <modelVersion>4.0.0</modelVersion>
        <packaging>pom</packaging>
    
        <dependencies>
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.4.5</version>
            </dependency>
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>5.1.30</version>
            </dependency>
            <dependency>
                <groupId>log4j</groupId>
                <artifactId>log4j</artifactId>
                <version>1.2.17</version>
            </dependency>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
                <scope>test</scope>
            </dependency>
        </dependencies>
    </project>

**2. SqlMapConfig.xml配置**

<?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="mysql">
            <environment id="mysql">
                
                <transactionManager type="jdbc"></transactionManager>
                
                <dataSource type="pooled">
                    <property name="driver" value="com.mysql.jdbc.Driver"></property>
                    <property name="url" value="jdbc:mysql:///mybatis?characterEncoding=utf8"></property>
                    <property name="username" value="root"></property>
                    <property name="password" value="root"></property>
                </dataSource>
            </environment>
        </environments>
    
    	
    	
        <mappers>
            <mapper resource="com/zz/dao/UserDao.xml"></mapper>
        </mappers>
    </configuration>

**3. 实体类**

public class User{ }

**4. dao接口**

public interface UserDao { 
    
        void save(User user);
    
        void update(User user);
    
        void delete(int id);
    
        User findOne(int id);
    
        List<User> findByname(String username);
    }

**5. 接口映射.xml文件**

<?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.zz.dao.UserDao">
    
        
        
        
        
        <insert id="save" parameterType="com.zz.entity.User">
            insert into user(username,birthday,sex,address) values(#{username},#{birthday},#{sex},#{address})
        </insert>
    
        <update id="update" parameterType="com.zz.entity.User">
            update user set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address}
                where id=#{id}
        </update>
    
        
        
        <delete id="delete" parameterType="int">
            delete from user where id=#{id}
        </delete>
    
        
        
        
        <select id="findOne" parameterType="int" resultType="com.zz.entity.User">
            select * from user where id=#{id}
        </select>
    
        
        <select id="findByname" parameterType="java.lang.String" resultType="com.zz.entity.User">
            select * from user where username like #{username}
        </select>
    
    </mapper>

#### 二、Mybatis输入/输出参数 ####

**1. 输入与输出参数**

<select id="findOne" parameterType="int" resultType="com.zz.entity.User">
        select * from user where id=#{id}
    </select>

*  输入参数：`parameterType`，对应方法的形参
 *  输出参数：`resultType`，对应方法的返回值类型

**2. parameterType**

*  **java简单类型作为输入参数**  
    ![parameterType简单类型.png][parameterType_.png]
 *  **pojo类型作为输入参数**  
    `POJO（Plain Ordinary Java Object）`简单的Java对象，实际就是普通JavaBean  
    ![parameterType pojo类型.png][parameterType pojo_.png]
 *  **pojo包装类型作为输入参数**  
    pojo包装类型：一个对象里面又包含了另外一个对象  
    ![parameterType pojo包装类型.png][parameterType pojo_.png 1]

**3. resultType**

*  **java简单类型作为输出参数**  
    ![resultType简单类型.png][resultType_.png]
 *  **pojo类型作为输出参数**  
    `resultType`指定方法返回对象（pojo类型）![resultType对象类型.png][resultType_.png 1]

**4. resultMap**  
　　通过resultType作为输出参数时，可以把查询的结果自动封装为对象，但是要求数据库中的列名称要与对象的属性一致，否则不能正确封装数据。此时可以使用`resultMap`，设置列与属性的映射关系，从而解决列与属性不一致时不能正确封装数据的问题。  
![resultMap.png][]

#### 三、SqlMapperConfig.xml 配置文件详解 ####

<table> 
 <thead> 
  <tr> 
   <th>配置标签名称</th> 
   <th>说明</th> 
   <th>作用</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><code>properties</code></td> 
   <td>属性</td> 
   <td>加载外部的配置文件</td> 
  </tr> 
  <tr> 
   <td>settings</td> 
   <td>配置全局参数</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td><code>typeAliases</code></td> 
   <td>类型别名</td> 
   <td>配置别名，给类指定别名</td> 
  </tr> 
  <tr> 
   <td>typeHandlers</td> 
   <td>类型处理器</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>objectFactory</td> 
   <td>对象工厂</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>plugins</td> 
   <td>插件</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>environments</td> 
   <td>环境集合属性对象</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>databaseIdProvider</td> 
   <td>多数据库支持</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td><code>mappers</code></td> 
   <td>映射器</td> 
   <td>配置加载接口的映射文件或接口类</td> 
  </tr> 
 </tbody> 
</table>

注意：在sqlMapConfig.xml中必须是从上往下的配置顺序

[parameterType_.png]: https://i.loli.net/2019/06/29/5d16cd4831dcc57034.png
[parameterType pojo_.png]: https://i.loli.net/2019/06/29/5d16cd481e45e93458.png
[parameterType pojo_.png 1]: https://i.loli.net/2019/06/29/5d16ccb75a1d536056.png
[resultType_.png]: https://i.loli.net/2019/06/29/5d16da8e8c96a10904.png
[resultType_.png 1]: https://i.loli.net/2019/06/29/5d16da8e9a9c411706.png
[resultMap.png]: https://i.loli.net/2019/06/29/5d16dc93f178a96657.png