2.第一个Mybatis程序

思路：环境搭建–>导入Mybatis–>编写代码–>测试！

参考官方文档入门https://mybatis.org/mybatis-3/zh/getting-started.html

2.1搭建环境

1.搭建数据库

create table user(
	id int(20) not null,
	name VARCHAR(30) DEFAULT NULL,
	pwd VARCHAR(30) DEFAULT NULL,
	PRIMARY KEY(id)
	);
	
	INSERT INTO USER(id,name,pwd) VALUES
	(1,'张三','123456'),
	(2,'李四','123123'),
	(3,'王五','009090')

2.新建普通Maven项目

3.删除src目录（这里是父工程）

4.导入依赖

<!--mysql驱动-->
   <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
   <dependency>
       <groupId>mysql</groupId>
       <artifactId>mysql-connector-java</artifactId>
       <version>5.1.46</version>
   </dependency>
   <!--Mybatis-->
   <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
   <dependency>
       <groupId>org.mybatis</groupId>
       <artifactId>mybatis</artifactId>
       <version>3.4.6</version>
   </dependency>

   <!--junit-->
   <!-- https://mvnrepository.com/artifact/junit/junit -->
   <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
       <version>4.12</version>
       <scope>test</scope>
   </dependency>

2.2创建一个模块

• 导入核心配置文件（mybatis-config.xml）并配置

  <!--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_test"/>
                  <property name="username" value="root"/>
                  <property name="password" value="liwenjie"/>
              </dataSource>
          </environment>
      </environments>
  </configuration>

2.3编写代码

• 实体类

  package com.lwj.pojo;
  
  public class User {
      private int id;
      private String name;
      private String pwd;
  
      public User(int id, String name, String pwd) {
          this.id = id;
          this.name = name;
          this.pwd = pwd;
      }
  
      public User() {
      }
  
      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;
      }
  }

• Dao接口

  public interface UserDao {
      User getUser();
  
  }

• 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">
  <mapper namespace="org.mybatis.example.UserMapper">
      <select id="selectUser" resultType="pojo.User">
      select * from user where id = #{id}
    </select>
  </mapper>

2.4测试

注意点1：

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

解决方案：

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

注意点2：

maven由于他的约定大于配置，我们可能会遇到我们写的配置文件，无法被导出或者生效的问题

解决方案：

<!--在build中配置resources，来防止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>

• 执行测试类

  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 org.junit.Test;
  import pojo.User;
  
  import java.io.InputStream;
  
  public class Test1 {
      @Test
      public void test() throws Exception{
  
          String resource = "mybatis-config.xml";
          InputStream inputStream = Resources.getResourceAsStream(resource);
          SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
  
          SqlSession session = sqlSessionFactory.openSession();
          User user = (User) session.selectOne("org.mybatis.example.UserMapper.selectUser", 1);
  
          System.out.println(user.getName());
      }
  }