名誉过高，实在是一种害人的负担——福尔特尔
教程网址：https://spring.io/guides/gs/accessing-data-jpa
首先访问 [pre-initialized project](https://start.spring.io/#!type=maven-project&language=java&platformVersion=3.0.1&packaging=jar&jvmVersion=17&groupId=com.example&artifactId=accessing-data-jpa&name=accessing-data-jpa&description=Demo project for Spring Boot&packageName=com.example.accessing-data-jpa&dependencies=data-jpa,h2)
直接点击GENERATE
下载下来，解压并打开项目
首先新建一个Customer类
package com.example.accessingdatajpa; import jakarta.persistence.Entity; import jakarta.persistence.GeneratedValue; import jakarta.persistence.GenerationType; import jakarta.persistence.Id; @Entity public class Customer { @Id @GeneratedValue(strategy=GenerationType.AUTO) private Long id; private String firstName; private String lastName; protected Customer() {} public Customer(String firstName, String lastName) { this.firstName = firstName; this.lastName = lastName; } @Override public String toString() { return String.format( "Customer[id=%d, firstName='%s', lastName='%s']", id, firstName, lastName); } public Long getId() { return id; } public String getFirstName() { return firstName; } public String getLastName() { return lastName; } }
然后编写一个简单的查询
package com.example.accessingdatajpa; import java.util.List; import org.springframework.data.repository.CrudRepository; public interface CustomerRepository extends CrudRepository<Customer, Long> { List<Customer> findByLastName(String lastName); Customer findById(long id); }
在主启动类注入一个demo
package com.example.accessingdatajpa; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class AccessingDataJpaApplication { private static final Logger log = LoggerFactory.getLogger(AccessingDataJpaApplication.class); public static void main(String[] args) { SpringApplication.run(AccessingDataJpaApplication.class, args); } @Bean public CommandLineRunner demo(CustomerRepository repository) { return (args) -> { // save a few customers repository.save(new Customer("Jack", "Bauer")); repository.save(new Customer("Chloe", "O'Brian")); repository.save(new Customer("Kim", "Bauer")); repository.save(new Customer("David", "Palmer")); repository.save(new Customer("Michelle", "Dessler")); // fetch all customers log.info("Customers found with findAll():"); log.info("-------------------------------"); for (Customer customer : repository.findAll()) { log.info(customer.toString()); } log.info(""); // fetch an individual customer by ID Customer customer = repository.findById(1L); log.info("Customer found with findById(1L):"); log.info("--------------------------------"); log.info(customer.toString()); log.info(""); // fetch customers by last name log.info("Customer found with findByLastName('Bauer'):"); log.info("--------------------------------------------"); repository.findByLastName("Bauer").forEach(bauer -> { log.info(bauer.toString()); }); // for (Customer bauer : repository.findByLastName("Bauer")) { // log.info(bauer.toString()); // } log.info(""); }; } }
执行主启动类的main方法启动项目，成功输出
== Customers found with findAll(): Customer[id=1, firstName='Jack', lastName='Bauer'] Customer[id=2, firstName='Chloe', lastName='O'Brian'] Customer[id=3, firstName='Kim', lastName='Bauer'] Customer[id=4, firstName='David', lastName='Palmer'] Customer[id=5, firstName='Michelle', lastName='Dessler'] == Customer found with findById(1L): Customer[id=1, firstName='Jack', lastName='Bauer'] == Customer found with findByLastName('Bauer'): Customer[id=1, firstName='Jack', lastName='Bauer'] Customer[id=3, firstName='Kim', lastName='Bauer']
