空指针异常 仓库 Spring Boot JPA

huangapple
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英文:

NullPointer Exception Repository Spring Boot Jpa

问题

以下是您提供的代码的翻译部分：

主类：

  1. @SpringBootApplication
  2. public class ExampleApplication {
  3.     
  4.     @Autowired
  5.     private static DataRepository dataRepository;
  6.     
  7.     public static void main(String[] args) {
  8.         SpringApplication.run(ExampleApplication.class, args);
  9.         System.out.println(dataRepository.findAll());
  10.     }
  11. }

模型：

  1. @Entity
  2. public class Data {
  3.  
  4.     @Id
  5.     private Long id;
  6.     private String content;
  7.     
  8.     public Data(Long id, String content) {
  9.         super();
  10.         this.id = id;
  11.         this.content = content;
  12.     }
  13.     
  14.     public Long getId() {
  15.         return id;
  16.     }
  17.     
  18.     public void setId(Long id) {
  19.         this.id = id;
  20.     }
  21.     
  22.     public String getContent() {
  23.         return content;
  24.     }
  25.     
  26.     public void setContent(String content) {
  27.         this.content = content;
  28.     }
  29.     
  30.     @Override
  31.     public String toString() {
  32.         return "Data [id=" + id + ", content=" + content + "]";
  33.     }
  34. }

仓库：

  1. @Repository
  2. public interface DataRepository extends JpaRepository<Data, Long> {
  3.     
  4. }

控制器：

  1. @RestController
  2. public class DataController {
  3.     
  4.     @Autowired
  5.     private DataRepository dataRepository;
  6.     
  7.     @GetMapping("/show")
  8.     public List<Data> findCities(Data data) {
  9.         return dataRepository.findAll();
  10.     }
  11. }

错误信息：

  1. 2020-04-07 10:27:14.323  INFO 19892 --- [           main] com.example.demo.ExampleApplication      : 启动 ExampleApplication，进程ID为 19892（位于 C:\Users\David\Documents\workspace-spring-tool-suite-4-4.5.1.RELEASE\example\target\classes，由 David 在 C:\Users\David\Documents\workspace-spring-tool-suite-4-4.5.1.RELEASE\example 启动）
  2. 2020-04-07 10:27:14.326  INFO 19892 --- [           main] com.example.demo.ExampleApplication      : 未设置活动配置文件，回退到默认配置文件: default
  3. 2020-04-07 10:27:14.739  INFO 19892 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : 以默认模式引导 Spring Data JPA 仓库。
  4. 2020-04-07 10:27:14.794  INFO 19892 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : 在 48 毫秒内完成 Spring Data 仓库扫描。找到 1 个 JPA 仓库接口。
  5. ...

请注意，上述翻译可能不包括代码中的所有细节，但已涵盖您所提供的内容。如果您有任何问题或需要更多翻译，请随时告知。

英文:

I am making a basic application to send an insert to a database, as a test I have been executing a simple findAll () to test the repository, but it always gives me NullPointer
I am aware that it is something very basic and also that I am missing something.
Thank you.

This is the main

  1.     @SpringBootApplication
  2. public class ExampleApplication {
  3. 	
  4.     @Autowired
  5.     private static DataRepository dataRepository;
  6. 	
  7. 	public static void main(String[] args) {
  8. 		SpringApplication.run(ExampleApplication.class, args);
  9. 		System.out.println(dataRepository.findAll());
  11. 	}
  13. }

Model

  1.  @Entity
  2. public class Data {
  3.  
  4.     @Id
  5.     private Long id;
  6.     private String content;
  7.     
  8.     
  9. 	public Data(Long id, String content) {
  10. 		super();
  11. 		this.id = id;
  12. 		this.content = content;
  13. 	}
  14. 	public Long getId() {
  15. 		return id;
  16. 	}
  17. 	public void setId(Long id) {
  18. 		this.id = id;
  19. 	}
  20. 	public String getContent() {
  21. 		return content;
  22. 	}
  23. 	public void setContent(String content) {
  24. 		this.content = content;
  25. 	}
  26. 	@Override
  27. 	public String toString() {
  28. 		return &quot;Data [id=&quot; + id + &quot;, content=&quot; + content + &quot;]&quot;;
  29. 	}
  30. }

Repository

  1.     @Repository
  2. public interface DataRepository extends JpaRepository&lt;Data, Long&gt; {
  3. 	    
  4. }

Controller

  1.  @RestController
  2. public class DataController {
  4.     @Autowired
  5.     private DataRepository dataRepository;
  7.     @GetMapping(&quot;/show&quot;)
  8.     public List&lt;Data&gt; findCities(Data data) {
  10.     
  11.         return dataRepository.findAll();
  12.     }
  13. }

Error

  1. 2020-04-07 10:27:14.323  INFO 19892 --- [           main] com.example.demo.ExampleApplication      : Starting ExampleApplication on DESKTOP-ARNRCSA with PID 19892 (C:\Users\David\Documents\workspace-spring-tool-suite-4-4.5.1.RELEASE\example\target\classes started by David in C:\Users\David\Documents\workspace-spring-tool-suite-4-4.5.1.RELEASE\example)
  2. 2020-04-07 10:27:14.326  INFO 19892 --- [           main] com.example.demo.ExampleApplication      : No active profile set, falling back to default profiles: default
  3. 2020-04-07 10:27:14.739  INFO 19892 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JPA repositories in DEFAULT mode.
  4. 2020-04-07 10:27:14.794  INFO 19892 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 48ms. Found 1 JPA repository interfaces.
  5. 2020-04-07 10:27:15.147  INFO 19892 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
  6. 2020-04-07 10:27:15.261  INFO 19892 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
  7. 2020-04-07 10:27:15.300  INFO 19892 --- [           main] o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: default]
  8. 2020-04-07 10:27:15.363  INFO 19892 --- [           main] org.hibernate.Version                    : HHH000412: Hibernate ORM core version 5.4.12.Final
  9. 2020-04-07 10:27:15.490  INFO 19892 --- [           main] o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {5.1.0.Final}
  10. 2020-04-07 10:27:15.588  INFO 19892 --- [           main] org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.MySQL55Dialect
  11. 2020-04-07 10:27:15.832  INFO 19892 --- [           main] org.hibernate.tuple.PojoInstantiator     : HHH000182: No default (no-argument) constructor for class: com.example.demo.Data (class must be instantiated by Interceptor)
  12. 2020-04-07 10:27:16.057  INFO 19892 --- [           main] o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
  13. 2020-04-07 10:27:16.063  INFO 19892 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit &#39;default&#39;
  14. 2020-04-07 10:27:16.066  INFO 19892 --- [           main] f.a.AutowiredAnnotationBeanPostProcessor : Autowired annotation is not supported on static fields: private static com.example.demo.DataRepository com.example.demo.ExampleApplication.dataRepository
  15. 2020-04-07 10:27:16.417  INFO 19892 --- [           main] com.example.demo.ExampleApplication      : Started ExampleApplication in 2.399 seconds (JVM running for 3.041)
  16. Exception in thread &quot;main&quot; java.lang.NullPointerException
  17. 	at com.example.demo.ExampleApplication.main(ExampleApplication.java:17)
  18. 2020-04-07 10:27:16.422  INFO 19892 --- [extShutdownHook] j.LocalContainerEntityManagerFactoryBean : Closing JPA EntityManagerFactory for persistence unit &#39;default&#39;
  19. 2020-04-07 10:27:16.424  INFO 19892 --- [extShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
  20. 2020-04-07 10:27:16.428  INFO 19892 --- [extShutdownHook] com.zaxxer.hikari.HikariDataSource

答案1

得分: 1

尝试一下这个：

  1. 尝试这个
  3.     @SpringBootApplication
  4. 	public class ExampleApplication {
  5. 	    public static void main(String[] args) {
  6. 	     	ConfigurableApplicationContext context = SpringApplication.run(Application.class, args);
  7. 	     	DataRepository dataRepository = context.getBean(DataRepository.class);
  8. 	     	System.out.println(dataRepository.findAll());
  9. 	    }
  10. 	}
  12. 除非您使用`postConstruct`，否则无法在静态字段上使用`autowire`。
英文:

try this

  1. @SpringBootApplication
  2. public class ExampleApplication {
  3.     public static void main(String[] args) {
  4.      	ConfigurableApplicationContext context = SpringApplication.run(Application.class, args);
  5.      	DataRepository dataRepository = context.getBean(DataRepository.class);
  6.      	System.out.println(dataRepository.findAll());
  7.     }
  8. }

you can not use autowire with static field unless you use postConstruct

答案2

得分: 0

Jpa 需要默认构造函数，因此将其放入你的数据类中。

英文:

Jpa needs defaut constructor so put it into your Data class

huangapple
  • 本文由 发表于 2020年4月7日 16:13:37
  • 转载请务必保留本文链接：https://go.coder-hub.com/61075571.html
  • api
  • java
  • spring
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