MyBatis学习笔记（一）创建第一个MyBatis项目

一、新建Maven项目

http://www.mybatis.org/mybatis-3/zh/index.html 该链接为MyBatis官方地址

创建MyBatis项目主要有两种办法，一种是导入jar包，可在github上下载https://github.com/mybatis/mybatis-3/releases。另一种方法就是现在比较常用的，也是官方推荐的maven导入。

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

下面我以IDEA来构建一个简单的MyBatis入门案例

无需选择任何模板直接next即可

直接next到finish即可

二、mybatis配置相关xml文件

pom.xml需要加上必须的MyBatis、junit、mysql连接驱动，这些都可以在maven官网上找到https://mvnrepository.com/

 <?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">
     <modelVersion>4.0.0</modelVersion>

     <groupId>com.mybatis.demo</groupId>
     <artifactId>demo1</artifactId>
     <version>1.0-SNAPSHOT</version>
     <dependencies>
         <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
         <dependency>
             <groupId>org.mybatis</groupId>
             <artifactId>mybatis</artifactId>
             <version>3.5.0</version>
         </dependency>
         <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
         <dependency>
             <groupId>mysql</groupId>
             <artifactId>mysql-connector-java</artifactId>
             <version>5.1.47</version>
         </dependency>
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
             <version>4.12</version>
             <scope>test</scope>
         </dependency>
     </dependencies>

 </project>

然后在main目录下的resources文件夹内新建mybatis-config.xml文件用来存放mybatis配置信息，和mapper文件夹用户存放映射文件

下为mybatis-config.xml文件

 <?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.jdbc.Driver"/>
                 <property name="url" value="jdbc:mysql://localhost:3306/mybatis_test"/>
                 <property name="username" value="root"/>
                 <property name="password" value="${password}"/>
             </dataSource>
         </environment>
     </environments>
     <!--映射配置文件路径-->
     <mappers>
         <mapper resource="mapper/userMapper.xml"/>
     </mappers>
 </configuration>

三、实现mybatis

我这里就使用navicat创建了一个简单的user表

在IDEA中创建一个user实体类，并且生成getter setter方法

 public class User {
     private int id;
     private String username;
     private String password;

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getUsername() {
         return username;
     }

     public void setUsername(String username) {
         this.username = username;
     }

     public String getPassword() {
         return password;
     }

     public void setPassword(String password) {
         this.password = password;
     }
 }

编写userMapper映射文件

 <?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">
 <!--
     用于定义一个映射文件的根节点
     namespace属性是用来配置命名空间
     resultType是sql映射文件中定义返回值类型
 -->
 <mapper namespace="com.mybatis.demo.User">
     <select id="userList" resultType="com.mybatis.demo.User">
       select * from users
     </select>
 </mapper>

编写测试类

 import com.mybatis.demo.User;
 import org.apache.ibatis.io.Resources;
 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 import org.junit.Test;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;

 public class myBatisTestDemo {
     @Test
     public void demo1(){
         try {
             //引入配置文件
             InputStream io=Resources.getResourceAsStream("mybatis-config.xml");
             //创建sqlSessionFactory对象
             SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(io);
             SqlSession sqlSession=sqlSessionFactory.openSession();
             List<User> lists=sqlSession.selectList("userList");
             System.out.println(lists.size());
         } catch (IOException e) {
             e.printStackTrace();
         }
     }

 }