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Note/JAVA/JAVA EE/Web程序设计笔记10——第六章：初识MyBatis.md

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2023-08-31 11:30:31 +08:00
# 第6章：MyBatis
Spring: 负责实现业务层的逻辑
MyBatis：主要和数据库打交道
Spring MVC：主要负责前端页面
## 6.1 MyBatis
1.持久层框架： 负责数据库开发
2.ORM框架：Object/Relational Mapping
3.POJO(Plain Old Java Object)：普通的Java对象
PO(Persisent Object):持久化对象
## 6.2
## 6.3
## 6.4 MyBatis的入门程序
基于MyBatis的客户管理系统的设计与实现
### 系统功能：
```java
1. 根据id查询客户
2. 根据姓名模糊查询
3. 添加客户
4. 更新客户
5. 删除客户
```
### 程序准备：
#### （1）mysql中创建数据库mybatis,表t_customer,插入数据。
```mysql
create database mybatis;
```
```mysql
create table t_customer(
id int (32) primary key auto_increment,
username varchar(50),
jobs varchar(50),
phone varchar(16)
);
```
```mysql
insert into t_customer values
('1','joy','doctor','13745874578'),
('2','jack','teacher','13521210112'),
('3','tom','worker','15179405961');
```
![image-20220405130626049](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405130626049.png)
#### （2）创建项目，导2个包：mybatis mysql-connector-java
```java
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.2</version>
</dependency>
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.28</version>
<!-- 版本号与自己mysql版本一致-->
</dependency>
```
#### （3）创建持久化类（实体类）
作用：和表进行数据转换
-- 增：实体类对象 转换 表中的记录
-- 查：表中的记录 转换 实体类对象
注意：成员变量的名字、数据类型 需要和 表中字段的名字、数据类型 保持一致
生成setter、getter 和 toString()方法
```java
package com.gzh.po;
public class Customer {
private int id;
private String username;
private String jobs;
private String phone;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getJobs() {
return jobs;
}
public void setJobs(String jobs) {
this.jobs = jobs;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
@Override
public String toString() {
return "Customer{" +
"id=" + id +
", username='" + username + '\'' +
", jobs='" + jobs + '\'' +
", phone='" + phone + '\'' +
'}';
}
}
```
#### （4）在resources文件夹下创建CustomerMapper.xml文件，用来写sql语句
##### 1.首先创建模板
在 file （文件）中的 setting （设置）中搜索 File and Code Templates （文件和代码模板），在其中首页 Files （文件）下创建文件 Mapper.xml，然后在下面填入以下代码，选择 OK （确定） 退出
```java
<?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="">
</mapper>
```
![image-20220405131535640](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405131535640.png)
##### 2.创建CustomerMapper.xml文件
在 resources 文件夹右击选择 new（新建）Mapper
![image-20220405132203804](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405132203804.png)
##### 3.写sql语句
```java
1.namespace属性的值：copy path（复制路径/引用）中 file name(文件名),去掉.xml
<mapper namespace="CustomerMapper">
2.#{id}占位符
3.parameterType是来设置占位符对应的参数的数据类型
4.resultType用来设置接收查询结果的持久化类，注意的是resultType属性值是全类名（全限定名）
<select id="findCustomerById" parameterType="int"resultType="com.gzh.po.Customer">
select * from t_customer where id=#{id}
</select>
```
![image-20220405132451651](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405132451651.png)
#### （5）在resources文件夹下创建mybatis-config.xml文件，该文件是MyBatis框架的配置文件
##### 1.首先创建模板
在 file （文件）中的 setting （设置）中搜索 File and Code Templates （文件和代码模板），在其中首页 Files （文件）下创建文件 mybatis-config.xml，然后在下面填入以下代码，选择 OK （确定） 退出
```java
<?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>
</configuration>
```
![image-20220405131954150](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405131954150.png)
##### 2.创建mybatis-config.xml文件
在 resources 文件夹右击选择 new（新建）mybatis-config
![image-20220405132528897](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405132528897.png)
##### 3.配置MyBatis框架
```java
<configuration>
<!-- 1.连接数据库-->
<environments default="mysql">
<environment id="mysql">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<!-- 四个成员变量不能错-->
<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="8520"/>
</dataSource>
</environment>
</environments>
<!-- 2.加载Mapper文件-->
<mappers>
<!-- resource 从 copy path（复制路径/引用）中 file name(文件名)-->
<mapper resource="CustomerMapper.xml"/>
</mappers>
</configuration>
```
![image-20220405132915669](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405132915669.png)
#### （6）单元测试：查询
在 com.gzh.po 包下创建测试类MybatisTest
1.加载配置文件和 Mapper 文件
通过 CustomerMapper.xml 文件中的 select 的 id 的值来命名测试类
![image-20220405133745512](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405133745512.png)
在输入 **Resources** 时通过提示导入名为 org 开头的包
![image-20220405134057509](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405134057509.png)
在此输入完此行代码后 getResourceAsStream 会爆红，不用管后续处理
```java
InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
```
##### 2.构建会话工厂
```java
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
```
##### 3.构建会话 SqlSession
```java
SqlSession sqlSession = sqlSessionFactory.openSession();
```
因为要测试多个方法，所以将以上构造剪切到**成员变量**
![image-20220405134848712](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405134848712.png)
##### 4.处理爆红错误
将鼠标放置到爆红的 resourceAsStream 处 Alt+回车 处理问题，选择添加类默认构造函数签名的异常
![image-20220405134938312](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405134938312.png)
##### 5.导包 Test ，并写完查询类
selectOne（）中的参数 = CustomerMapper.xml文件中 namespace + select id
MybatisTest.java 总体代码如下：
```java
package com.gzh.po;
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 java.io.IOException;
import java.io.InputStream;
public class MybatisTest {
InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
public MybatisTest() throws IOException {
}
@Test
public void findCustomerById(){
// s: = CustomerMapper.xml文件中 namespace + select id
Customer o = sqlSession.selectOne("CustomerMapper.findCustomerById", 1);
System.out.println(o);
}
}
```
运行结果如下：
![image-20220405135447683](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220405135447683.png)
### 1.根据id查询客户
```java
<select id="findCustomerById" parameterType="int" resultType="com.gzh.po.Customer">
select * from t_customer where id=#{id}
</select>
```
```java
@Test
public void findCustomerById() {
Customer o = sqlSession.selectOne("com.CustomerMapper.findCustomerById", 1);
System.out.println(o);
}
```
![image-20220407152029547](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152029547.png)
### 2.根据姓名模糊查询
```java
<select id="findCustomerByName" parameterType="String" resultType="com.gzh.po.Customer">
select * from t_customer where username like '%${value}%'
</select>
```
```java
@Test
public void findCustomerByName() {
List<Customer> o = sqlSession.selectList("CustomerMapper.findCustomerByName", "j");
for (Customer customer : o){
System.out.println(customer);
}
}
```
![image-20220407152044583](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152044583.png)
### 3.添加客户
```java
<insert id="addCustomer" parameterType="com.gzh.po.Customer">
insert into t_customer values (#{id},#{username},#{jobs},#{phone})
</insert>
```
```java
@Test
public void addCustomer(){
Customer customer = new Customer();
customer.setId(1);
customer.setUsername("zhangsan");
customer.setJobs("student");
customer.setPhone("110");
sqlSession.insert("CustomerMapper.addCustomer",customer);
sqlSession.commit();//只要更改数据库中的数据，就需要调用该方法完成数据的
sqlSession.close();//关闭数据库的连接
}
```
![image-20220407152231144](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152231144.png)
### 4.更新客户
```java
<update id="updateCustomer" parameterType="com.gzh.po.Customer">
update t_customer set username = #{username},jobs = #{jobs},phone = #{phone} where id = #{id}
</update>
```
```java
@Test
public void updateCustomer() {
Customer customer = new Customer();
customer.setId(4);
customer.setUsername("zhangsan");
customer.setJobs("teacher");
customer.setPhone("18888888888");
sqlSession.update("CustomerMapper.updateCustomer", customer);
sqlSession.commit();
sqlSession.close();
}
```
![image-20220407152334704](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152334704.png)
### 5.删除客户
```java
<delete id="deleteCustomer" parameterType="int">
delete from t_customer where id = #{id}
</delete>
```
```java
@Test
public void deleteCustomer() {
sqlSession.delete("CustomerMapper.deleteCustomer", 1);
sqlSession.commit();
sqlSession.close();
}
```
![image-20220407152346163](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152346163.png)
### 如何在控制台输入SQL语句？
(1) 导包 log4j
```java
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
```
(2) 复制log4j.properties文件到resources.文件夹下
(3) resources下新建directory,名为com
(4) 将CustomerMapper.xml文件复制到com下
![image-20220407152650898](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152650898.png)
(5) 复制后的CustomerMapper.Xml中的namespacel的值修改：com.CustomerMapper
![image-20220407152719404](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152719404.png)
(6) 修改mybatis-config.xml文件中resource属性的值：
![image-20220407152735127](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152735127.png)
(7) 修改测试方法中的值：
![image-20220407152802930](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152802930.png)
运行测试结果如下：
![image-20220407152822914](https://yovinchen-1308133012.cos.ap-beijing.myqcloud.com/image-20220407152822914.png)