MyBatis-02-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,'狂神','123456'),
(2,'张三','123456'),
(3,'李四','123890')

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

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <!--父工程-->
    <groupId>com.rui</groupId>
    <artifactId>MyBatis-Study</artifactId>
    <version>1.0-SNAPSHOT</version>

    <!--导入依赖-->
    <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.17</version>
        </dependency>
        <!--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>

</project>

<!--在build中配置resources，来防止我们资源导出失败的问题-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

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配置环境组-->
      <!--default默认环境-->
      <environments default="development">
          <!--environment单个环境-->
          <environment id="development">
              <!--transactionManager配置事务管理器-->
              <transactionManager type="JDBC"/>
              <!--配置连接池-->
              <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=UFT-8"/>
                  <property name="username" value="root"/>
                  <property name="password" value="Cc105481"/>
              </dataSource>
          </environment>
      </environments>
  
  </configuration>
  

• 编写mybatis工具类

package com.rui.utils;

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

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

//sqlSessionFactory--->SessionFactory
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";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            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。
    // 你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

2.3、编写代码

• 实体类

  package com.rui.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接口

  package com.rui.dao;
  
  import com.rui.pojo.User;
  
  import java.util.List;
  
  public interface UserDao {
      List<User> getUserList();
  }
  
  

• 接口实现类由原来的UserImpl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mapper接口-->
<mapper namespace="com.rui.dao.UserDao">
    <!--select查询语句-->
   <select id="getUserList" resultType="com.rui.pojo.User">
       /*定义sql*/
       select * from mybatis.user
   </select>
</mapper>

2.4、测试

注意点：

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

MapperRegistry是什么?

核心配置文件中注册mappers

• junit测试

  package com.rui;
  
  import com.rui.dao.UserDao;
  import com.rui.pojo.User;
  import com.rui.utils.MyBatisUtils;
  import org.apache.ibatis.session.SqlSession;
  import org.junit.Test;
  
  import java.util.List;
  
  public class UserDaoTest {
      @Test
      public void test(){
          //第一步：获得SqlSession对象
          SqlSession sqlSession = MyBatisUtils.getSqlSession();
          //执行SQL
          UserDao mapper = sqlSession.getMapper(UserDao.class);
          List<User> userList = mapper.getUserList();
          for (User user : userList) {
              System.out.println(user);
          }
          //关闭SqlSession
          sqlSession.close();
      }
  }
  
  

  可能会遇到的问题：

  1. 配置文件没有注册
  2. 绑定接口错误
  3. 方法名不对
  4. 返回类型不对
  5. Maven导出资源问题