第一個Mybatis程式

• 思路：搭建環境—>匯入Mybatis—>編寫程式碼—>測試！

• 2.1、搭建環境

  2.1.1、搭建資料庫

CREATE TABLE `Users`(
 `id` INT(10) NOT NULL,
 `name` VARCHAR(30) NOT NULL,
 `pwd` VARCHAR(30) NOT NULL,
 PRIMARY KEY(`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO `Users`(`id`,`name`,`pwd`) VALUES
(1,'王五','123456'),
(2,'張三','123423'),
(3,'李四','123456');

2.1.2、新建專案

• 新建了一個普通的 maven 專案
• 刪除 src 目錄
• 匯入maven依賴

<!--匯入依賴-->
<dependencies>
    <!--Mysql驅動-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.22</version>
    </dependency>
    <!--mybatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.3</version>
    </dependency>
    <!--junit -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>

2.2、建立一個模組

2.2.1、編寫mybatis的核心配置檔案

<?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-->
<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/shop?useUnicode=true&amp;characterEncoding=utf8&amp;useSSL=true&amp;serverTimezone=Asia/Shanghai"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
</configuration>

2.2.2、編寫mybatis工具類

//sqlSessionFactory --> sqlSession
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try{
            //使用Mybatis第一步：獲取aqlSessionFactory物件
            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，顧名思義，我們可以從中獲得 SqlSession 的例項。
    // SqlSession 提供了在資料庫執行 SQL 命令所需的所有方法。
    // 你可以通過 SqlSession 例項來直接執行已對映的 SQL 語句。
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

2.3、編寫程式碼

2.3.1、實體類

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 String getName() {
        return name;
    }
    public String getPwd() {
        return pwd;
    }
    public void setId(int id) {
        this.id = id;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
}

2.3.2、Dao介面

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

2.3.3、介面實現類

由原來的UserDaoImpl轉變為一個Mapper配置檔案

<?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.saxon.dao.UseDao">
    
    <select id="getUserList" resultType="com.saxon.pojo.User">
        select * from users
    </select>
</mapper>

測試

注意一點：

org.apache.ibatis.binding.BindingException: Type interface com.chen.dao.UseDao is not known to the MapperRegistry.

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

public class UserDaoTest extends TestCase {
    @Test
    public void test(){
        //第一步：獲得SqlSession物件
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        try {
            //執行sql
            //方式一：getMapper
            UserDao userDao = sqlSession.getMapper(UserDao.class);
            List<User> userList = userDao.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
        }finally {
            //關閉SqlSession
            sqlSession.close();
        }
    }
}

2.4.1、junit測試

• 資源過濾問題 在pom.xml新增下面配置

<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>

可能會遇到的問題：

1. 配置檔案沒有註冊
2. 繫結介面錯誤。
3. 方法名不對
4. 返回型別不對
5. Maven匯出資源問題