什么是MyBatis

• MyBatis 是一款優(yōu)秀的持久層框架
• MyBatis 是一個半自動化的ORM框架（Object Relationship Mapping對象關(guān)系映射）
• MyBatis 避免了幾乎所有的 JDBC 代碼和手動設(shè)置參數(shù)以及獲取結(jié)果集的過程
• MyBatis 可以使用簡單的 XML 或注解來配置和映射原生信息，將接口和 Java 的 實體類 【Plain Old Java Objects,普通的 Java對象】映射成數(shù)據(jù)庫中的記錄。

持久層

完成持久化工作的代碼塊，我們可以簡單理解為DAO層（Data Access Object數(shù)據(jù)訪問對象）

大多數(shù)情況下，數(shù)據(jù)持久化意味著將內(nèi)存中的數(shù)據(jù)保存到磁盤上加以固化，這主要是通過關(guān)系型數(shù)據(jù)庫來完成

MyBatis第一個程序

整體流程：

1.搭建MySQL數(shù)據(jù)庫環(huán)境

2.導入MyBatis依賴

3.編寫代碼

4.測試

代碼演示

1.搭建數(shù)據(jù)庫環(huán)境

CREATE DATABASE `mybatis`;

USE `mybatis`;

DROP TABLE IF EXISTS `user`;

CREATE TABLE `user` (
  `id` int(20) NOT NULL,
  `name` varchar(30) DEFAULT NULL,
  `pwd` varchar(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `user`(`id`,`name`,`pwd`) values (1,'王小二','123456'),(2,'張三','abcdef'),(3,'李四','987654');

2.導入MyBatis依賴

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.2</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.47</version>
</dependency>

3.編寫MyBatis核心配置文件 "mybatis-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.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="cn/whb/dao/userMapper.xml"/>
    </mappers>
</configuration>

4.創(chuàng)建實體類

public class User {
    
    private int id;  //id
    private String name;   //姓名
    private String pwd;   //密碼
    
    //構(gòu)造,有參,無參
    //set/get
    //toString()
    
}

5.編寫Mapper接口類

import com.kuang.pojo.User;
import java.util.List;

public interface UserMapper {
    List<User> selectUser();
}

6.編寫Mapper.xml配置文件

• namespace 十分重要，他需要映射到對應(yīng)的Mapper接口，不能寫錯！

<?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="cn.whb.dao.UserMapper">
  <select id="selectUser" resultType="cn.whb.pojo.User">
    select * from user
  </select>
</mapper>

7.編寫測試類

public class MyTest {
    @Test
    public void selectUser() {
        //獲取配置文件的流對象，交給SqlSessionFactoryBuilder并解析
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        
        //sqlSessionFactory--->相當于數(shù)據(jù)庫連接池
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        
        //相當于每一個數(shù)據(jù)庫連接對象Connection
        SqlSession session = sqlSessionFactory.openSession();
        //方法一:
        //List<User> users = session.selectList("cn.whb.mapper.UserMapper.selectUser");
        //方法二:
        UserMapper mapper = session.getMapper(UserMapper.class);
        List<User> users = mapper.selectUser();

        for (User user: users){
            System.out.println(user);
        }
        session.close();
    }
}

8.問題說明

可能出現(xiàn)問題說明：Maven靜態(tài)資源過濾問題，在pom.xml中添加如下：

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