[英][Java| SpringBoot]The Repository is not getting injected
幾年后,我再次進入 Java,只處理 javascript 和 typescript,我正試圖進入 Spring Boot。
這聽起來很有趣也很方便,但我正在嘗試做一些簡單的事情,但由於某種原因我無法將我的存儲庫注入到我的服務中。 這聽起來很簡單,但我已經挖掘了幾個小時,但無法讓它工作。我想知道你們中的一些人是否可以幫助我理解我做錯了什么。
提前致謝
項目(實體)
package com.example.demo.modules.projects.entities;
import javax.persistence.*;
@Entity
@Table
public class Projects {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column
private String project_name;
@Column
private String description;
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getProject_name() {
return project_name;
}
public void setProject_name(String project_name) {
this.project_name = project_name;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
}
資料庫
package com.example.demo.modules.projects.repositories;
import com.example.demo.modules.projects.entities.Projects;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
@Repository
public interface IProjectRepository extends JpaRepository<Projects, Long> {
}
創建項目服務
package com.example.demo.modules.projects.services;
import com.example.demo.modules.projects.entities.Projects;
import com.example.demo.modules.projects.repositories.IProjectRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class CreateProjectService {
@Autowired
IProjectRepository iProjectRepository;
public Projects execute(Projects project){
System.out.println("Received " + project.toString());
Projects CreatedProject= this.iProjectRepository.save(project);
System.out.println("Created " + CreatedProject);
return CreatedProject;
}
}
錯誤
它似乎沒有正確注入/實例化。
2020-10-09 00:56:08.774 ERROR 5856 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException: Cannot invoke "com.example.demo.modules.projects.repositories.IProjectRepository.save(Object)" because "this.iProjectRepository" is null] with root cause
java.lang.NullPointerException: Cannot invoke "com.example.demo.modules.projects.repositories.IProjectRepository.save(Object)" because "this.iProjectRepository" is null
at com.example.demo.modules.projects.services.CreateProjectService.execute(CreateProjectService.java:17) ~[classes/:na]
at com.example.demo.ServerApplication.newEmployee(ServerApplication.java:26) ~[classes/:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:564) ~[na:na]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105) ~[spring-webmvc-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:878) ~[spring-webmvc-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:792) ~[spring-webmvc-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:652) ~[tomcat-embed-core-9.0.38.jar:4.0.FR]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.38.jar:4.0.FR]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.38.jar:9.0.38]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.9.RELEASE.jar:5.2.9.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130) ~[na:na]
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630) ~[na:na]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.38.jar:9.0.38]
at java.base/java.lang.Thread.run(Thread.java:832) ~[na:na]
問題是因為您不允許 Spring 實例化CreateProjectService
並控制 bean,可能您使用new CreateProjectService()
實例化了 object。
推薦的方法是創建一個接口,例如ICreateProjectService
,如下所示:
public interface ICreateProjectService {
Projects execute(Projects project);
}
然后在CreateProjectService
中實現ICreateProjectService
,如下所示:
@Service
public class CreateProjectService implements ICreateProjectService {
@Autowired
private IProjectRepository iProjectRepository;
@Override
public Projects execute(Projects project) {
System.out.println("Received " + project.toString());
Projects CreatedProject= this.iProjectRepository.save(project);
System.out.println("Created " + CreatedProject);
return CreatedProject;
}
}
然后在您的 Controller 層中,作為服務使用示例,通過注入接口自動裝配您的服務,如下所示:
@Restcontroller
@RequestMapping("/api/v1")
public class CreateProjectRest {
@Autowired
private ICreateProjectService iCreateProjectService;
@PostMapping
public Projects execute(Projects project) {
createProjectService.execute(project);
// your code here
}
}
現在 Spring 能夠將CreateProjectService
識別為具體實現,將其實例化為 Spring bean,將其保存在 Spring 容器中,並使其可用於任何注入的依賴注入。
希望這會有所幫助。
更新:
通過構造函數而不是字段或 setter 方法注入依賴項更為可取。
@Restcontroller
@RequestMapping("/api/v1")
public class CreateProjectRest {
private ICreateProjectService iCreateProjectService;
/* No needed to annotate @Autowired after Spring 4.3.*/
public CreateProjectRest(ICreateProjectService iCreateProjectService){
this.iCreateProjectService = iCreateProjectService;
}
@PostMapping
public Projects execute(Projects project) {
createProjectService.execute(project);
// your code here
}
}
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