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01、MyBatis HelloWorld

2020-06-07 02:18 573 查看

1. MyBatis简介

1)MyBatis 是支持定制化 SQL、存储过程以及高级映射的优秀的持久层框架

2)MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集

3)MyBatis可以使用简单的XML或注解用于配置和原始映射,将接口和Java的POJO(Plain Old Java Objects,普通的 Java 对象)映射成数据库中的记录

2. 使用 MyBatis原因

1)JDBC

(1)SQL 夹在 Java 代码块里,耦合度高导致硬编码内伤

(2)维护不易且实际开发需求中 sql 是有变化,频繁修改的情况多见

2)Hibernate 和 JPA

(1)长难复杂 SQL,对于 Hibernate 而言处理也不容易

(2)内部自动生产的 SQL,不容易做特殊优化

(3)基于全映射的全自动框架,大量字段的 POJO 进行部分映射时比较困难。导致数据库性能下降

3)MyBatis

(1)对开发人员而言,核心 sql 还是需要自己优化

(2)sql 和 java 编码分开,功能边界清晰,一个专注业务、一个专注数据

3. MyBatis下载

1)下载网址

https://github.com/mybatis/mybatis-3/

<?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) \n" />
</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>
log4j.xml 2)创建Mysql测试表

-- 创建库

CREATE DATABASE test_mybatis;

-- 使用库

USE test_mybatis;

-- 创建表

CREATE TABLE tbl_employee(

  id INT(11) PRIMARY KEY AUTO_INCREMENT,

  last_name VARCHAR(50),

  email VARCHAR(50),

  gender CHAR(1)

);

3)Employee

  使用Employee接收数据库的记录. 

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 + "]";
}
}
Employee.java

4)配置文件

(1)参考MyBatis官方手册

<?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="root123" />
</dataSource>
</environment>
</environments>

<!-- !!!!!!!!!非常重要!!!!!!!!!!!! -->
<!-- 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中 -->
<mappers>
<mapper resource="EmployeeMapper.xml" />
</mappers>

</configuration>
MyBatis-config.xml (2)创建MyBatis的SQL映射文件

<?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="com.atguigu.mybatis.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="selectEmp" resultType="com.atguigu.mybatis.bean.Employee">
select id,last_name lastName,email,gender from tbl_employee where id = #{id}
</select>
</mapper>
EmployeeMapper.xml 5)测试

(1) 构建 SqlSessionFactory

  根据全局配置文件,利用SqlSessionFactoryBuilder创建SqlSessionFactory 

public interface EmployeeMapper {
public Employee getEmpById(Integer id);
}
EmployeeMapper.java
@Test
public void test1() throws IOException {

//1. 获取SQLSessionFactory对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

//2.获取sqlsession对象
SqlSession openSession = sqlSessionFactory.openSession();

//3.获取接口的实现类对象 接口的类对象会为接口自动的创建一个代理对象,代理对象去执行增删改查方法
try {
EmployeeMapper mapper =  openSession.getMapper(EmployeeMapper.class);
Employee employee = mapper.getEmpById(1);
System.out.println(mapper.getClass());
System.out.println(employee);
} finally {
openSession.close();
}

}
EmployeeTest.java
<select id="getEmpById" resultType="com.atguigu.mybatis.bean.Employee">
select id,last_name lastName,email,gender from tbl_employee where id = #{id}
</select>
EmployeeMapper.xml  参考文档:https://mybatis.org/mybatis-3/zh/getting-started.html

https://github.com/mybatis/mybatis-3/

 

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