BeginnerQuestion Spring and MongoDB findAll - spring

Question

I'm a Beginner with Spring and MongoDB and just tried to write a Class "Person" which has firstName and LastName and ID.
#Document(collection = "persons")
public class Person {
#org.springframework.data.annotation.Id
private String Id;
private String firstName;
private String lastName;
private int age = 0;
public Person(String firstName, String lastName){
this.firstName = firstName;
this.lastName = lastName;
}
And I connect to a MongoDB with this Interface:
public interface PersonRepository extends MongoRepository<Person, String> {
And the Personcontroller should return all Persons which are in the database collection named "persons":
#RestController
public class PersonController {
private PersonRepository repo;
#GetMapping("/persons")
public ResponseEntity getAllPersons(){
return ResponseEntity.ok(repo.findAll());
}
}
So in my Mongo Database are 2 Persons:
_id:5ed7b666eabc4b2a9474fd61
firstName:"Rick"
lastName:"Sanchez"
age:0
_class:"com.petziferum.backend.model.Person"
_id:5ed7b666eabc4b2a9474fd62
firstName:"Morty"
lastName:"Smith"
age:0
_class:"com.petziferum.backend.model.Person"
But if I send a Get Request to localhost:8000/persons, I get an Error 500 and can't find my Mistake.
Can someone help me please? Cant even find any easy Documentations without search functions and all that.
I just want an Array list or Object List in return when requesting /persons
Stacktrace:
"trace": "java.lang.NullPointerException\r\n
\tat com.petziferum.backend.controller.PersonController.getAllPersons(PersonController.java:24)\r\n
\tat sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)\r\n
\tat sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)\r\n
\tat sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)\r\n
\tat java.lang.reflect.Method.invoke(Method.java:498)\r\n
\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)\r\n
\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)\r\n
\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105)\r\n
\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:879)\r\n
\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793)\r\n
\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\r\n
\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)\r\n
\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)\r\n
\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)\r\n
\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)\r\n
\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:634)\r\n
\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)\r\n
\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:741)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)\r\n
\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)\r\n
\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\r\n
\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)\r\n
\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\r\n
\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)\r\n
\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\r\n
\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)\r\n
\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)\r\n
\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)\r\n
\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)\r\n
\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)\r\n
\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)\r\n
\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)\r\n
\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)\r\n
\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)\r\n
\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)\r\n
\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)\r\n
\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)\r\n
\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590)\r\n
\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)\r\n
\tat java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)\r\n
\tat java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)\r\n
\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)\r\n
\tat java.lang.Thread.run(Thread.java:745)\r\n",
"message": "No message available",
"path": "/persons/"
}

Answer 1

Your repo is null. You need to inject your repo into your controller either by using constructor injection or #Autowired.