Spring Boot 整合JPA

Spring Boot 整合了JPA来访问数据库。在这个示例中，将创建一个简单的实体类User，并使用JPA来进行数据库操作。

首先，pom.xml

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId>
</dependency>

创建一个实体类User，并使用JPA注解来映射到数据库表：

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;@Entity
public class User {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private Long id;private String username;private String email;// 构造函数、getter和setter方法
}

创建一个JPA Repository接口，继承自JpaRepository，以便进行数据库操作：

import org.springframework.data.jpa.repository.JpaRepository;public interface UserRepository extends JpaRepository<User, Long> {// 在这里可以添加自定义查询方法
}

创建一个Controller类来处理HTTP请求：

import com.lfsun.demolfsunstudyjpa.dao.UserRepository;
import com.lfsun.demolfsunstudyjpa.entity.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;import java.util.List;
import java.util.Optional;@RestController
@RequestMapping("/users")
public class UserController {@Autowiredprivate UserRepository userRepository;// 获取所有用户@GetMappingpublic List<User> getAllUsers() {return userRepository.findAll();}// 根据ID获取单个用户@GetMapping("/{id}")public User getUserById(@PathVariable Long id) {return userRepository.findById(id).orElse(null);}// 创建新用户@PostMappingpublic User createUser(@RequestBody User user) {return userRepository.save(user);}// 根据ID删除用户@DeleteMapping("/{id}")public void deleteUser(@PathVariable Long id) {userRepository.deleteById(id);}// 更新用户信息@PutMapping("/{id}")public ResponseEntity<User> updateUser(@PathVariable Long id, @RequestBody User updatedUser) {// 查找现有用户Optional<User> existingUserOptional = userRepository.findById(id);if (!existingUserOptional.isPresent()) {// 如果用户不存在，返回404 Not Found响应return ResponseEntity.notFound().build();}User existingUser = existingUserOptional.get();// 更新用户信息existingUser.setUsername(updatedUser.getUsername());existingUser.setEmail(updatedUser.getEmail());// 保存更新后的用户信息User savedUser = userRepository.save(existingUser);// 返回更新后的用户信息和200 OK响应return ResponseEntity.ok(savedUser);}}

配置application.properties或application.yml文件以指定数据库连接信息：

spring:datasource:url: jdbc:mysql://localhost:3306/study_jpa?useUnicode=true&characterEncoding=UTF-8&useSSL=falseusername: rootpassword: 123321driver-class-name: com.mysql.cj.jdbc.Driverjpa:hibernate:ddl-auto: updateshow-sql: true