Mybatis的創建 (IDEA版)

1.安裝maven

在官網https://archive.apache.org/dist/maven/maven-3/3.6.1/binaries 下載maven的3.6.1版本(apache-maven-3.6.1-bin.zip)，

解壓 maven 壓縮包至一個沒有中文的路徑下，并找一個位置創建倉庫檔案夾 修改\apache-maven-3.6.1\conf中的setting.xml檔案,
配置本地倉庫地址 打開idea在其中配置mave（路徑選擇自己maven所在路徑），file-settings-maven之后點擊ok

2.配置Mybatis

1. 查看官方檔案.
2. 匯入MAVEN依賴(在pom.xml檔案中配置)

<dependencies>
	<dependency>
	    <groupId>mysql</groupId>
	    <artifactId>mysql-connector-java</artifactId>
	    <version>5.1.47</version>
	</dependency>
	
	<dependency>
	    <groupId>org.mybatis</groupId>
	    <artifactId>mybatis</artifactId>
	    <version>3.5.2</version>
	</dependency>
	
	<dependency>
	    <groupId>junit</groupId>
	    <artifactId>junit</artifactId>
	    <version>3.8.1</version>
	    <scope>test</scope>
	</dependency>
		 </dependencies>

不要怕報錯,maven會根據你的配置下載依賴
點擊重繪按鈕會建立dependencies檔案保存從中央倉庫下載的依賴

3. 配置mybatis組態檔

基礎代碼在官方檔案里有

<?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">
<!--核心組態檔-->
<configuration>
<!--    配置環境-->
    <environments default="development">
        <environment id="development">
<!--            事物管理.默認JDBC-->
            <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;userUnicode=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>

4. 配置資料庫(我用的是mysql)
   
   
   填好用戶名,密碼后點擊測驗,成功則連接成功

5. 創建MybatisUtils(讀取上述的組態檔mybatis-config.xml)

public class MybatisUtils {

    //提升作用域
    private static SqlSessionFactory sqlSessionFactory;

    static {
        //獲取sqlSessionFactory物件
        String resource = "org/mybatis/example/mybatis-config.xml";
        //官方檔案中的Resources.getResourceAsStream(resource)會報錯,應該為以下:
        InputStream inputStream = Resources.class.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }
    //既然有了 SqlSessionFactory，顧名思義，我們可以從中獲得 SqlSession 的實體，
    //SqlSession 提供了在資料庫執行 SQL 命令所需的所有方法，
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

6. 撰寫代碼

• 物體類

package com.fww.pojo;
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介面

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

• UserMapper(由原來的Dao介面實作類UserDaoImpl的模式變為Mapper組態檔)
  

<?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">
<!--namespace系結一個Dao/Mapper介面-->
<mapper namespace="com.fww.dao.UserDao">
<!--id等于之前介面里面的名字;
    resultType等于介面里的回傳型別(注意只能寫全類名)-->
    <select id="getUserList" resultType="com.fww.pojo.User">
        select * from mybatis.user 
    </select>
</mapper>

3.測驗

public class UserDaoTest {
    @Test
    public void test() {
        //獲得SqlSession物件
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //執行Sql,面向介面編程只需要拿到介面物件即可
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        //關閉SqlSession
        sqlSession.close();
    }
}

結果
`User{id=1, name='fww', pwd='123456'}
User{id=2, name='wq', pwd='123456'}
User{id=3, name='jcl', pwd='123450'}`

5. 記錄bug

1. Error：java：錯誤：不支持發行版本 5（或寫著其他版本的~）

在pom.xml檔案中添加以下代碼:

    <properties>
        <java.version>14</java.version>
        <maven.compiler.source>${java.version}</maven.compiler.source>
        <maven.compiler.target>${java.version}</maven.compiler.target>
    </properties>

2. 沒有取到SqlSession(例外為空指標)
   可能是導錯包了(折磨了好久,哎~~)

錯誤 :import sun.security.util.Resources;
正確:import org.apache.ibatis.io.Resources;

3. Maven靜態資源過濾問題

在pom.xml檔案中匯入以下代碼

<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>

4. PersistenceException

改組態檔mybatis中useSSL=false

5. org.apache.ibatis.binding.BindingException