第一個MyBatis程序

搭建數據庫：

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,'汪瑞傑','123456'),
(2,'汪瑞傑','528582'),
(3,'汪瑞傑','286353');

新建項目（maven）

導入mybatis，mysql，junit依賴 pom.xml

編寫mybaits核心配置文件：mybatis.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">
  
  <!-- 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?useUnicode=ture&amp;characterEncoding=UTF-8&amp;serverTimezone=GMT%2B8"/>
        <property name="username" value="root"/>
        <property name="password" value="344165"/>
      </dataSource>
    </environment>
  </environments>
</configuration>

編寫mybatis核心工具類:

package com.perwrj.utils;

import java.io.IOException;
import java.io.InputStream;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

/**
 * (工廠模式)sqlSessionFactory --> sqlSession
 * @author wangruijie
 *
 */
public class MyBatisUtil {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            //獲取SqlSessionFactory對象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            // TODO: handle exception
        }
    }
    
    
//    既然有了 SqlSessionFactory，顧名思義，咱們能夠從中得到 SqlSession 的實例。
//    SqlSession 提供了在數據庫執行 SQL 命令所需的全部方法。
//    你能夠經過 SqlSession 實例來直接執行已映射的 SQL 語句
    
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
         
    }
}

編寫代碼：

• 實體類

package com.perwrj.pojo;

public class User {
    private int id;
    private String name;
    private String pwd;
    public User() {
        super();
        // TODO Auto-generated constructor stub
    }
    public User(int id, String name, String pwd) {
        super();
        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 + "]";
    }
    
}

• UserMapper接口（原UserDao.java）

package com.perwrj.dao;

import java.util.List;

import com.perwrj.pojo.User;

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

• UserMapper.xml配置文件（原UserDaoImpl實現類轉換的Mapper文件）

<?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綁定一個對應的Mapper/Dao接口 -->
<mapper namespace="com.perwrj.dao.UserMapper">
<!-- 查詢 id=「重寫的方法名」 resultType=「返回值類型（全類名）」 -->
  <select id="getUserList" resultType="com.perwrj.pojo.User">
    select * from mybatis.user
  </select>
</mapper>

測試（junit）：

編寫測試文件

package com.perwrj.dao;

import java.util.List;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import com.perwrj.pojo.User;
import com.perwrj.utils.MyBatisUtil;

public class UserMapperTest {
    @Test
    public void test() {
        //得到SqlSession對象，
        SqlSession sqlSession = MyBatisUtil.getSqlSession();
        
        try {
//            方式一：getMapper執行sql:更加簡潔，類型更加安全，推薦使用
            
              UserMapper userMapper = sqlSession.getMapper(UserMapper.class); List<User>
              userList = userMapper.getUserList();
            
              for (User user : userList) { System.out.println(user); }
    
            //方式一結束
            
//            方式二：老方法，不建議使用，
            /*
             * List<User> list =
             * sqlSession.selectList("com.perwrj.dao.UserMapper.getUserList");
             * 
             * for (User object : list) { System.out.println(object); }
             */
            //方式二結束
        }catch(Throwable e) {
            e.printStackTrace();
        }finally {
//            關閉sqlSession
            sqlSession.close();
        }    
    }
}

org.apache.ibatis.binding.BindingException: Type interface com.perwrj.dao.UserMapper is not known to the MapperRegistry.（沒有在mybatis-config.xml核心配置文件中註冊Mapper）

 java.lang.ExceptionInInitializerError (初始化異常失敗，沒有找到UserMapper.xml文件)

可能遇到的錯誤

• 配置文件沒有註冊
• 綁定接口錯誤
• 方法名不對
• 返回值類型不對
• Maven導出資源問題

2021-02-24