MyBatis入门 + 接口式编程（idea实现）

1、由于是入门级demo,所以直接弄个java工程，也不用maven了

先来看工程的目录结构

这里学习下：

java中build path是什么?

如果你bai只是将jar包复制到Java工程里面去，那么是无法使用到jar包里面zhi的类，因为编程ide无法找到jar包。所以build path其实就是添加jar包的路径，让ide可以找到这个路径对应的jar包的文件，从而来能够使用jar包中的方法。

如何将lib中的jar包build path + idea如何将一个目录变成资源文件夹自行百度

2、java bean

package com.atguigu.mybatis.bean;

public class Employee {
   
   private Integer id;
   private String lastName;
   private String email;
   private String gender;
   
   
   public Integer getId() {
      return id;
   }
   public void setId(Integer id) {
      this.id = id;
   }
   public String getLastName() {
      return lastName;
   }
   public void setLastName(String lastName) {
      this.lastName = lastName;
   }
   public String getEmail() {
      return email;
   }
   public void setEmail(String email) {
      this.email = email;
   }
   public String getGender() {
      return gender;
   }
   public void setGender(String gender) {
      this.gender = gender;
   }
   @Override
   public String toString() {
      return "Employee [id=" + id + ", lastName=" + lastName + ", email="
            + email + ", gender=" + gender + "]";
   }
}

3、mybatis的全局配置文件 + sql映射文件+ log4j的配置文件

<?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>
   <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" />
            <property name="username" value="root" />
            <property name="password" value="houchen" />
         </dataSource>
      </environment>
   </environments>
   <!-- 将我们写好的sql映射文件（EmployeeMapper.xml）
   一定要注册到全局配置文件（mybatis-config.xml）中 -->
   <mappers>
      <mapper resource="EmployeeMapper.xml" />
   </mappers>
</configuration>
===============================================================
<?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="com.atguigu.mybatis.mapper.EmployeeMapper">
<!-- 
namespace:名称空间;指定为接口的全类名
id：唯一标识
resultType：返回值类型
#{id}：从传递过来的参数中取出id值

public Employee getEmpById(Integer id);
 -->
   <select id="getEmpById" resultType="com.atguigu.mybatis.bean.Employee">
      select id,last_name lastName,email,gender from tbl_employee where id = #{id}
   </select>
</mapper>
===============================================================
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
 
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
 
 <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
   <param name="Encoding" value="UTF-8" />
   <layout class="org.apache.log4j.PatternLayout">
    <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m  (%F:%L) 
" />
   </layout>
 </appender>
 <logger name="java.sql">
   <level value="debug" />
 </logger>
 <logger name="org.apache.ibatis">
   <level value="info" />
 </logger>
 <root>
   <level value="debug" />
   <appender-ref ref="STDOUT" />
 </root>
</log4j:configuration>
4、mapper 接口
public interface EmployeeMapper {

    public Employee getEmpById(int id);
}

4、mapper 接口

public interface EmployeeMapper {

    public Employee getEmpById(int id);
}

5、测试代码

/*
    1、sqlSession代表和数据库的一次会话，用完必须关闭
    2、SqlSession是非线程安全的，每次使用都应该创建一个新的对象
    3、mapper接口没有实现类，但是mybatis会为这个接口生成一个代理对象
    4、两个重要的配置文件：
        mybatis的全局配置文件
        sql映射文件
 */
public class MybatisTest {

    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        return sqlSessionFactory;
    }


    /*
     * 1、根据xml配置文件（mybatis的全局配置文件）创建一个SqlSessionFactory对象
     * 2、sql映射文件
     * 3、将sql映射文件注册到mybatis全局配置文件
     */
    @Test
    public void test() throws IOException {
        SqlSession openSession = getSqlSessionFactory().openSession();
        try {
            Employee employee = openSession.selectOne(
                    "com.atguigu.mybatis.dao.EmployeeMapper.getEmpById", 1);
            System.out.println(employee);
        } finally {
            openSession.close();
        }
    }

    @Test
    public void testMapper() throws IOException {
        SqlSession openSession = getSqlSessionFactory().openSession();
        EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
        Employee e = mapper.getEmpById(1);
        System.out.println(e);
    }

}