idea Spring Boot项目使用JPA创建与数据库链接

1.pom.xml文件中添加依赖

		<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId></dependency><dependency><groupId>com.mysql</groupId><artifactId>mysql-connector-j</artifactId><scope>runtime</scope></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-test</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId></dependency>

2.创建entity文件，用于创建用户类（User）

3.entity文件夹下创建用户类

User代码如下：

package com.example.demo.entity;import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;@Entity
@Table(name = "tb_user")
public class User {@Id@Column(name = "f_id")private Integer id;@Column(name = "f_username", unique = true, nullable = false, length = 16)private String username;@Column(name = "f_password", length = 32, nullable = false)private String password;@Column(name = "f_name", length = 64)private String name;@Column(name = "f_age")private Integer age;@Column(name = "f_phone", length = 11)private String phone;}

4.resources文件夹下创建application.yml文件

配置数据库连接信息（一定要保证username、password与自己所使用数据库信息一致）

application.yml文件下代码：

sever:port: 8080
spring:datasource:driver-class-name: com.mysql.cj.jdbc.Driverurl: jdbc:mysql://localhost:3306/db_qfnu_test1username: rootpassword: 123456jpa:hibernate:ddl-auto: updateshow-sql: true

Server 配置：

server: port: 8080

这部分配置指定了应用程序的服务器配置，该应用程序将在本地监听8080端口。
Spring 数据源配置：

spring: datasource: driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://localhost:3306/db_qfnu_test username: root password: 123456

这一部分配置了Spring框架中的数据源，用于连接数据库。
- driver-class-name: 指定数据库驱动类，这里是MySQL的JDBC驱动。
- url: 数据库连接的URL，包括数据库类型、主机名、端口号和数据库名称。
- username 和 password: 数据库连接的用户名和密码。
Spring JPA 配置：

spring: jpa: hibernate: ddl-auto: update show-sql: true

这一部分配置了Spring Data JPA，用于简化数据访问层的开发。
- hibernate.ddl-auto: 指定Hibernate在启动时如何更新数据库表结构。在这里，设置为update表示 Hibernate 将尝试更新数据库表结构，但不会删除表或数据。
- show-sql: 将此属性设置为 true 将在控制台上打印出Hibernate执行的SQL语句，方便调试。

5.创建数据库

创建数据库代码：

进入数据库：mysql -u root -p
查看数据库：show databases;
创建新表： create database db_qfnu_test1;

6.运行代码

运行出成功截图：

7.实现对数据库与前端交互

在User类中创建方法

package com.example.demo.entity;import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;@Entity
@Table(name = "tb_user")
public class User {@Id@Column(name = "f_id")private Integer id;@Column(name = "f_username", unique = true, nullable = false, length = 16)private String username;@Column(name = "f_password", length = 32, nullable = false)private String password;@Column(name = "f_name", length = 64)private String name;@Column(name = "f_age")private Integer age;@Column(name = "f_phone", length = 11)private String phone;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getName() {return name;}public void setName(String name) {this.name = name;}public void setAge(int age) {this.age = age;}public void setPhone(String phone) {this.phone = phone;}
}

创建Dao文件夹，用于创建User接口

Dao文件夹下创建UserDAO接口，选择Interface

UserDAO代码：

package com.example.demo.Dao;import com.example.demo.entity.User;
import org.springframework.data.jpa.repository.JpaRepository;public interface UserDAO extends JpaRepository<User, Integer> {
}

创建UserController文件

UserController文件中编写Mapping，代码：

package com.example.demo.controller;import com.example.demo.Dao.UserDAO;
import com.example.demo.Dao.UserDAO;
import com.example.demo.entity.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;import java.util.Optional;@RestController
@RequestMapping("user")
public class UserController {@Autowiredprivate final UserDAO userDao;public UserController(UserDAO userDao){this.userDao = userDao;}@GetMapping("findById/{id}")public User findById(@PathVariable Integer id){Optional<User> userOptional = userDao.findById(id);return userOptional.orElse(null);   get or else}@PostMapping("add")public void add(User user){userDao.save(user);}@PostMapping("save")public String save(@RequestBody User user){userDao.save(user);return "success";}@PostMapping("removeById/{id}")public String removeById(@PathVariable Integer id){userDao.deleteById(id);return "success";}
}

数据库中添加表项：