[Java | SpringBoot]存储库没有被注入

在仅仅处理javascript和typescript的几年之后，我又开始接触Java，我正在尝试进入SpringBoot

这听起来很有趣，也很方便，但我正在尝试做一些简单的事情，由于某些原因，我无法将我的存储库注入到我的服务中。这听起来很简单，但我已经挖了好几个小时，没法让它工作。我想知道你们中的一些人能否帮助我理解我做错了什么，谢谢

提前谢谢

项目（实体）

存储库

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;
    }
}

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> {
    
}

错误

它似乎没有正确地注入/实例化

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]

---

问题是因为您不允许Spring实例化

CreateProjectService

并控制bean，可能是您用

new CreateProjectService（）

实例化了对象

该方法是创建一个接口，例如

ICreateProjectService

，如下所示：

public interface ICreateProjectService {

    Projects execute(Projects project);

}

@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;
    }
}

@Restcontroller
@RequestMapping("/api/v1")
public class CreateProjectRest {

    @Autowired
    private ICreateProjectService iCreateProjectService;

    @PostMapping
    public Projects execute(Projects project) {
        createProjectService.execute(project);
        // your code here
    }
}

然后在

CreateProjectService

中执行

ICreateProjectService

，如下所示：

public interface ICreateProjectService {

    Projects execute(Projects project);

}

@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;
    }
}

@Restcontroller
@RequestMapping("/api/v1")
public class CreateProjectRest {

    @Autowired
    private ICreateProjectService iCreateProjectService;

    @PostMapping
    public Projects execute(Projects project) {
        createProjectService.execute(project);
        // your code here
    }
}

然后在控制器层中，作为服务使用的一个示例，通过注入接口自动连接服务，如下所示：

public interface ICreateProjectService {

    Projects execute(Projects project);

}

@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;
    }
}

@Restcontroller
@RequestMapping("/api/v1")
public class CreateProjectRest {

    @Autowired
    private ICreateProjectService iCreateProjectService;

    @PostMapping
    public Projects execute(Projects project) {
        createProjectService.execute(project);
        // your code here
    }
}

现在，Spring能够将

CreateProjectService

识别为一个具体的实现，将其实例化为Springbean，将其保存在Spring容器中，并使其可用于依赖项注入

希望这能有所帮助

更新：

它更多的是通过构造函数而不是字段或setter方法注入依赖项

@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
    }
}

---

非常感谢你！它现在工作得很好，解释帮助我理解了什么是错的，为什么！！

CreateProjectService

没有问题，接口也不是必需的。主要问题可能是在控制器中执行

new CreateProjectService（）

，而不是自动连接。我同意@M。取消接口与否与控制反转或阻止任何人用新的东西实例化无关。我认为在这里使用接口是完全错误的。免费附加层