mybatis_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`;

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,'loading','12345'),
(2,'直直','12345'),
(3,'卷卷','12345')

新建项目

1. 新建一个普通的maven项目

2. 删除src目录

3. 导入maven依赖

    <!--导入依赖-->
       <dependencies>
           <!--mysql驱动-->
           <dependency>
               <groupId>mysql</groupId>
               <artifactId>mysql-connector-java</artifactId>
               <version>5.1.47</version>
           </dependency>
           <!--mybatis-->
           <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
           <dependency>
               <groupId>org.mybatis</groupId>
               <artifactId>mybatis</artifactId>
               <version>3.5.2</version>
           </dependency>
           <!--junit-->
           <dependency>
               <groupId>junit</groupId>
               <artifactId>junit</artifactId>
               <version>4.12</version>
           </dependency>
       </dependencies>

   2.2、创建一个模块

编写mybatis的核心配置文件

<?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">
<!--configuration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="123456"/>
            </dataSource>
        </environment>
    </environments>

</configuration>

编写mybatis工具类

//sqlSessionFactory --> sqlSession
public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    static{
        try {
            //使用Mybatis第一步：获取sqlSessionFactory对象
            String resource = "mybatis-config.xml";       //读取mybatis-config.xml配置文件
            InputStream inputStream = Resources.getResourceAsStream(resource);       //获取资源并输出成流
            //SqlSessionFactoryBuilder 则可以从 XML 配置文件或一个预先配置的 Configuration 实例来构建出 SqlSessionFactory 实例
            //SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
            //SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);       
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    //既然有了 SqlSessionFactory，顾名思义，我们就可以从中获得 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();
    }

}

编写代码

2.4、测试

注意点：

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

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MapperRegistry是什么？

核心配置文件中注册 mappers

 <!--每一个Mapper.XML都需要在Mybatis核心配置文件中注册！-->
    <mappers>
        <mapper resource="com/loading/dao/UserMapper.xml"/>
       <!-- <mapper class="com.loading.dao.UserMapper"/>-->
    </mappers>

你们可以能会遇到的问题：

 <!--每一个Mapper.XML都需要在Mybatis核心配置文件中注册！-->
    <mappers>
        <mapper resource="com/loading/dao/UserMapper.xml"/>
       <!-- <mapper class="com.loading.dao.UserMapper"/>-->
    </mappers>  

<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.loading.dao.UserDao">
    <select id="getUserList" resultType="com.loading.pojo.User">
        select * from mybatis.user;
    </select>
</mapper>

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

}
//接口和调接口方法的测试类对应

        //方式一：getMapper
        //UserDao userDao = sqlSession.getMapper(UserDao.class);
        //UserList<User> userList = userDao.getUserList();
        List<User> userList = sqlSession.getMapper(UserDao.class).getUserList();
        for (User user : userList) {
            System.out.println(user);
        }

import com.loading.dao.UserDao;
import com.loading.pojo.User;
import com.loading.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class MyTest {
    @Test
    public void test(){
        //第一步：获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        try {
            //方式一：getMapper 建议使用
            //UserDao userDao = sqlSession.getMapper(UserDao.class);
            //UserList<User> userList = userDao.getUserList();
            List<User> userList = sqlSession.getMapper(UserDao.class).getUserList();

            //方式二：利用sqlsqlSession中的方法绑定对应的接口中的相应方法，不建议使用
            //List<User> userList = sqlSession.selectList("com.loading.dao.UserDao.getUserList");

            for (User user : userList) {
                System.out.println(user);
            }
        }catch (Exception e){
           e.printStackTrace();
        }finally {
            //关闭SqlSession
            sqlSession.close();
        }

    }
}

<!--配置资源过滤，防止我们的xml文件无法导出-->
    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
            </resource>

            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
            </resource>
        </resources>
    </build>

官方建议格式：

• 实体类

  package com.kuang.pojo;
  
  //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转变为一个 Mapper配置文件.

  <?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=绑定一个对应的Dao/Mapper接口-->
  <mapper namespace="com.kuang.dao.UserDao">
  
  <!--select查询语句-->
     <select id="getUserList" resultType="com.loading.pojo.User">
         select * from mybatis.user
     </select>
  
  </mapper>
  

• junit测试

  @Test
  public void test(){
      //第一步：获得SqlSession对象
      SqlSession sqlSession = MybatisUtils.getSqlSession();
  
  
      //方式一：getMapper
      UserDao userDao = sqlSession.getMapper(UserDao.class);
      List<User> userList = userDao.getUserList();
  
      for (User user : userList) {
          System.out.println(user);
      }
  
  
  
      //关闭SqlSession
      sqlSession.close();
  }
  
  

• 配置文件没有注册
• 绑定接口错误。
• 方法名不对
• 返回类型不对
• Maven导出资源问题