2.第一个Mybatis程序

标签：values   jdbc   insert   type   util   private   工具   nts   password   

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

       <!--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=false&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";
              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。
      public static SqlSession  getSqlSession(){
          return sqlSessionFactory.openSession();
      }
  
  }
  
  

2.3、编写代码

• 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.kuang.pojo.User">
         select * from mybatis.user
     </select>
  
  </mapper>
  

2.4、测试

注意点：

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

MapperRegistry是什么？

每一个Mapper.xml 都需要在Mybatis核心配置文件中注册

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

核心配置文件中注册 mappers

• 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();
  }
  
  

你们可以能会遇到的问题：

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

   <!--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>
               <filtering>true</filtering>
           </resource>
           <resource>
               <directory>src/main/java</directory>
               <includes>
                   <include>**/*.properties</include>
                   <include>**/*.xml</include>
               </includes>
               <filtering>true</filtering>
           </resource>
       </resources>
   </build>
   

2.第一个Mybatis程序

标签：values   jdbc   insert   type   util   private   工具   nts   password   

原文地址：https://www.cnblogs.com/yhnCoder/p/13619931.html