MyBatis

1.什么是MyBatis

• Mybatis是一款优秀的持久层框架

• 它支持定制化SQL、存储过程以及高级映射

• MyBatis避免了几乎所有的JDBC代码和手动设置参数以及获得结果集

• MyBatis可以使用简单的XML或注解来配置和映射原生类型、接口和Java的POJO为数据库中的记录

• MyBatis本是apache的一个开源项目iBatis

如何获得Mybatis？

maven仓库：

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

2.第一个Mybatis程序

1.搭建环境

搭建数据库

CREATE DATABASE `mybatis`;
​
USE `mybatis`;
​
CREATE TABLE  `user`(`id` INT(20) NOT NULL PRIMARY KEY,`name` VARCHAR(30) DEFAULT NULL,`pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;
​
INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'张三','123456'),
(2,'李四','123456');

新建项目

1. 新建一个普通的maven项目

2. 删除src目录

3. 导入maven依赖

   <!--    导入依赖--><dependencies>
   <!--        mysql驱动--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.46</version></dependency>
   <!--        mybatis--><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.2</version></dependency>
   <!--        junit--><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version></dependency></dependencies>

2.创建一个模块

• 编写mybatis核心配置文件

  <?xml version="1.0" encoding="UTF-8" ?>
  <!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
  <!--configuration核心配置文件-->
  <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?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/><property name="username" value="root"/><property name="password" value="123456"/></dataSource></environment></environments>
  ​
  </configuration>

• 编写mybatis工具类

  //sqlSessionFactory --> sqlSession
  public class MybatisUtils {
  ​private static SqlSessionFactory sqlSessionFactory;
  ​static {try {//使用Mybatis第一步：获取sqlSessionFactory对象String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);} catch (IOException e) {e.printStackTrace();}}
  ​//既然有了 SqlSessionFactory，顾名思义，我们就可以从中获取 SqlSession 的实例了，//SqlSession 完全包含了面向数据库执行SQL命令所需的所有方法public static SqlSession getSqlSession() {return sqlSessionFactory.openSession();}
  }

3.编写代码

• 实体类

  //实体类
  public class User {private int id;private String name;private String pwd;
  ​public User() {}
  ​public User(int id, String name, String pwd) {this.id = id;this.name = name;this.pwd = pwd;}
  ​public int getId() {return id;}
  ​public void setId(int id) {this.id = id;}
  ​public String getName() {return name;}
  ​public void setName(String name) {this.name = name;}
  ​public String getPwd() {return pwd;}
  ​public void setPwd(String pwd) {this.pwd = pwd;}
  ​@Overridepublic String toString() {return "User{" +"id=" + id +", name='" + name + '\'' +", pwd='" + pwd + '\'' +'}';}
  }

• Dao接口

  public interface UserDao {List<User> getUserList();
  }

• 接口实现类由原来的UserDaoImpl转变为一个 Mapper配置文件

  <?xml version="1.0" encoding="UTF-8" ?>
  <!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  <!--namesapce=绑定一个对应的Dao/Mapper接口-->
  <mapper namespace="com.zkw.dao.UserDao"><select id="getUserList" resultType="com.zkw.pojo.User">select * from mybatis.user</select>
  </mapper>

4.测试

MapperRegistry是什么？

核心配置文件中注册 mappers

• junit测试

   @Testpublic void test(){//第一步：获取sqlSession对象SqlSession sqlSession = MybatisUtils.getSqlSession();//方式一：执行SQLUserDao mapper = sqlSession.getMapper(UserDao.class);List<User> userList = mapper.getUserList();
  ​for (User user : userList) {System.out.println(user);}
  ​//关闭sqlSessionsqlSession.close();}

可能遇到问题：

1. 配置文件没有注册

2. 绑定接口错误

3. 方法名不对

4. 返回类型不对

5. Maven到处资源问题

可以在pom.xml中加入：

    <build><resources><resource><directory>src/main/resources</directory><includes><include>**/*.properties</include><include>**/*.xml</include></includes><filtering>true</filtering></resource><resource><directory>src/main/java</directory><includes><include>**/*.properties</include><include>**/*.xml</include></includes><filtering>true</filtering></resource></resources></build>