第一个mybatis程序

2、第一个mybatis程序

思路：搭建环境--->导入mybatis--->编写代码--->测试！

2.1、搭建环境

搭建数据库

CREATE DATABASE `mybatis`;
USE `mybatis`;
INSERT INTO `user`(`id`,`name`,`pwd`)VALUES
(1,'张三','123456'),
(2,'李四','123456'),
(3,'王五','123545');

新建项目

1. 新建一个普通的maven项目
2. 删除src目录（成为父工程）

2.2、导入依赖

<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.13.2</version>
    <scope>test</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.25</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.7</version>
</dependency>

2.3、创建一个模块

• 编写mybatis核心配置文件

<?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">
<!--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="${root}"/>
                <property name="password" value="${root}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
</configuration>

• 编写mybatis工具类

public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            //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对象，我们就可以获得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();
    }
}

2.4、编写代码

• 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;
    }

    @Override
    public 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变为现在的UserMapper

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

2.5、测试

• Junit测试

public class UserDaoTest {
    @Test
    public void test(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }
}

这里的测试问题真的是百出！！！把我折腾了有半天

1. 一定要记住在核心配置中注册UserMapper，并且以这种格式，不然会报错，显示没有注册

<mappers>
    <mapper resource="com/kuang/dao/UserMapper.xml"/>
</mappers>

2. 由于maven的约定大于限制，我写的UserMapper.xml文件一定要在子父工程的pom.xml中添加这个，

<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>

3. 再就是遇到了一个奇葩中的奇葩问题，我一运行代码就报错，检查了所有代码没有任何问题，该更新的也都更新了，结果还是报错，结果最后在右边栏maven中点了个generate sources问题就解决了，我现在还不明白，整的我一头雾水。