学MyBatis看这四篇就够了！（1）之创建第一个MyBatis

MyBatis官网：https://mybatis.org/mybatis-3/zh/index.htm

1. 什么是Mybatis?MyBatis 是一款优秀的持久层框架，它支持自定义 SQL、存储过程以及高级映射。MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

我的第一个Mybatis程序

1. IDEA创建Maven项目

1. 1.

1. prom.xml中引入依赖，分三步，引入mybatis，引入MySQL驱动，引入junit

4. 引入mybatis

<dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.2</version> </dependency>

4. 引入MySQL驱动

<dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.22</version> </dependency>

4. 引入junit，用于java测试

<dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> </dependency> 8. 结果如图：点击如图 1. 编写mybatis-config.xml文件： 其中

1. driver是驱动名 1. url是MySQL的url 1. username是用户名 1. password是数据库用户的密码 1. mappers是每一个mapper都要配置的！！！切记！！！不能忘，一般每一个实例一个mapper

<?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?serverTimezone=Asia/Shanghai"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments> <!--每一个xml都要注册--> <mappers> <mapper resource="com/lwh/dao/UserMapper.xml"/> </mappers> </configuration> 7. 编写实体类 <pre><span class="token keyword">package</span> <span class="token namespace">com<span class="token punctuation">.</span>lwh<span class="token punctuation">.</span>pojo</span><span class="token punctuation">;</span> <span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">User</span> <span class="token punctuation">{ <!-- --></span> <span class="token keyword">private</span> <span class="token keyword">int</span> id<span class="token punctuation">;</span> <span class="token keyword">private</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span> <span class="token keyword">private</span> <span class="token class-name">String</span> pwd<span class="token punctuation">;</span> <span class="token keyword">public</span> <span class="token class-name">User</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{ <!-- --></span> <span class="token punctuation">}</span> （为了展示明了，简洁，展示时省略tostring和get，set方法，请读者误偷懒，否则报错） <span class="token punctuation">}</span> </pre>

编写dao层 UserDao： <pre><span class="token keyword">package</span> <span class="token namespace">com<span class="token punctuation">.</span>lwh<span class="token punctuation">.</span>dao</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">com<span class="token punctuation">.</span>lwh<span class="token punctuation">.</span>pojo<span class="token punctuation">.</span></span><span class="token class-name">User</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>util<span class="token punctuation">.</span></span><span class="token class-name">List</span><span class="token punctuation">;</span> <span class="token keyword">public</span> <span class="token keyword">interface</span> <span class="token class-name">UserDao</span> <span class="token punctuation">{ <!-- --></span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">User</span><span class="token punctuation">></span></span> <span class="token function">getUserList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> </pre> UserMapper： 其中

9. namespace是Dao接口的地址，包名.Dao名 10. select中的id是Dao层中的方法， 11. resultType是返回的实体类的方法 12. 最后select中包裹的是SQL语句

<?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.lwh.dao.UserDao"> <select id="getUserList" resultType="com.lwh.pojo.User"> select * from user </select> </mapper>

13. 编写工具类MyBatisUtils： <pre><span class="token keyword">package</span> <span class="token namespace">com<span class="token punctuation">.</span>lwh<span class="token punctuation">.</span>utils</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">org<span class="token punctuation">.</span>apache<span class="token punctuation">.</span>ibatis<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">Resources</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">org<span class="token punctuation">.</span>apache<span class="token punctuation">.</span>ibatis<span class="token punctuation">.</span>session<span class="token punctuation">.</span></span><span class="token class-name">SqlSession</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">org<span class="token punctuation">.</span>apache<span class="token punctuation">.</span>ibatis<span class="token punctuation">.</span>session<span class="token punctuation">.</span></span><span class="token class-name">SqlSessionFactory</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">org<span class="token punctuation">.</span>apache<span class="token punctuation">.</span>ibatis<span class="token punctuation">.</span>session<span class="token punctuation">.</span></span><span class="token class-name">SqlSessionFactoryBuilder</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">IOException</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">InputStream</span><span class="token punctuation">;</span> <span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">MybatisUtils</span> <span class="token punctuation">{ <!-- --></span> <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token class-name">SqlSessionFactory</span> sqlSessionFactory<span class="token punctuation">;</span> <span class="token keyword">static</span> <span class="token punctuation">{ <!-- --></span> <span class="token class-name">String</span> resource <span class="token operator">=</span> <span class="token string">"mybatis-config.xml"</span><span class="token punctuation">;</span><span class="token comment">//资源目录底下的mybatis的主配置文件</span> <span class="token class-name">InputStream</span> inputStream <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span> <span class="token keyword">try</span> <span class="token punctuation">{ <!-- --></span> inputStream <span class="token operator">=</span> <span class="token class-name">Resources</span><span class="token punctuation">.</span><span class="token function">getResourceAsStream</span><span class="token punctuation">(</span>resource<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//io流读取配置文件</span> <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{ <!-- --></span> e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> sqlSessionFactory <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">SqlSessionFactoryBuilder</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">build</span><span class="token punctuation">(</span>inputStream<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取一个sql工厂实例</span> <span class="token punctuation">}</span> <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">SqlSession</span> <span class="token function">getSqlSession</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{ <!-- --></span> <span class="token keyword">return</span> sqlSessionFactory<span class="token punctuation">.</span><span class="token function">openSession</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取一个会话实例</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span> </pre> 14. 编写测试类 在test目录下创建一个与dao层目录结构一样的目录（规范） <pre><span class="token keyword">package</span> <span class="token namespace">com<span class="token punctuation">.</span>lwh<span class="token punctuation">.</span>dao</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">com<span class="token punctuation">.</span>lwh<span class="token punctuation">.</span>pojo<span class="token punctuation">.</span></span><span class="token class-name">User</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">com<span class="token punctuation">.</span>lwh<span class="token punctuation">.</span>utils<span class="token punctuation">.</span></span><span class="token class-name">MybatisUtils</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">org<span class="token punctuation">.</span>apache<span class="token punctuation">.</span>ibatis<span class="token punctuation">.</span>session<span class="token punctuation">.</span></span><span class="token class-name">SqlSession</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">org<span class="token punctuation">.</span>junit<span class="token punctuation">.</span></span><span class="token class-name">Test</span><span class="token punctuation">;</span> <span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>util<span class="token punctuation">.</span></span><span class="token class-name">List</span><span class="token punctuation">;</span> <span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">UserDaoImpl</span> <span class="token punctuation">{ <!-- --></span> <span class="token annotation punctuation">@Test</span> <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{ <!-- --></span> <span class="token comment">//获取连接</span> <span class="token class-name">SqlSession</span> sqlSession<span class="token operator">=</span> <span class="token class-name">MybatisUtils</span><span class="token punctuation">.</span><span class="token function">getSqlSession</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//执行sql</span> <span class="token class-name">UserDao</span> userDao<span class="token operator">=</span>sqlSession<span class="token punctuation">.</span><span class="token function">getMapper</span><span class="token punctuation">(</span><span class="token class-name">UserDao</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">User</span><span class="token punctuation">></span></span> list<span class="token operator">=</span>userDao<span class="token punctuation">.</span><span class="token function">getUserList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token class-name">User</span> user<span class="token operator">:</span>list<span class="token punctuation">)</span> <span class="token punctuation">{ <!-- --></span> <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>user<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> sqlSession<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span> </pre> 15. 运行 代码目录：