JoinTable annotation causes NullPointerException

Question

I am writing an Address Book program as an exercise to understand join tables. When a user logs in with a username and password, they should be able to see a list of people who may or may not also be registered users.

Each Name record may be associated with a Credential record, but it is not required. Each Credential record must be associated with a Name record. I want this to be a one-to-one relationship. The reason I want to use a join table is to avoid having a join column in the Name table which would hold mostly null values, but also to understand a join table implementation.

Name Entity

package com.entity;

import lombok.*;

import javax.persistence.*;

@Getter @Setter
@ToString
@NoArgsConstructor
@AllArgsConstructor
@Entity
@Table(name = "name")
public class Name {

    @Id
    @Column(name = "name_id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Setter(AccessLevel.NONE)
    private int nameId;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinTable(name = "name_credential_jt",
            joinColumns = @JoinColumn(
                    name = "name_id_fk",
                    referencedColumnName = "name_id"),
            inverseJoinColumns = @JoinColumn(
                    name = "credential_id_fk",
                    referencedColumnName = "credential_id"))
    private Credential credential;

    public Name(String firstName, String lastName){
        super();
        this.firstName = firstName;
        this.lastName = lastName;
    }
    public Name(int nameId, String firstName, String lastName){
        super();
        this.nameId = nameId;
        this.firstName = firstName;
        this.lastName = lastName;
    }
}

Credential Entity

package com.entity;

import lombok.*;

import javax.persistence.*;

@Getter @Setter
@ToString
@NoArgsConstructor
@AllArgsConstructor
@Entity
@Table(name = "credential")
public class Credential {
    @Id
    @Column(name = "credential_id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Setter(AccessLevel.NONE)
    private int credentialId;

    @Column(name = "username")
    private String username;

    @Column(name = "password")
    private String password;

    @OneToOne(mappedBy = "credential")
    private Name name;

    public Credential(String username, String password, Name name){
        super();
        this.username = username;
        this.password = password;
        this.name = name;
    }
}

CredentialControl

@GetMapping("/setup")
public ResponseEntity<String> setup(){
    try{
        Name name1 = new Name("Abby", "Martin");
        NameService nameService = new NameService();
        System.out.println(name1);
        nameService.save(name1);
        name1 = nameService.findAll().get(0);
        Credential credential1 = new Credential("abs", "mar", name1);
        credentialService.save(credential1);
        return new ResponseEntity<>(HttpStatus.OK);
    } catch (Exception e){
        e.printStackTrace();
    }
    throw new RuntimeException();
}

Why does nameService.save(name1) throw a NullPointerException? Or rather, what have I done wrong, and how do I fix it? I believe that name1 contains the values (0, "Abby", "Martin", null), so I believe the NPE is coming from the null value of name1's credential field.

Finally, for reference, I have used a page from Baeldung as well as various Stack Exchange posts to figure this out, but I have not yet succeeded.

Stacktrace

Name(nameId=0, firstName=Abby, lastName=Martin, credential=null)
java.lang.NullPointerException
    at com.service.NameService.save(NameService.java:19)
    at com.control.CredentialControl.setup(CredentialControl.java:42)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1060)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:962)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:626)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:888)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1597)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)
2021-02-07 13:34:35.659 ERROR 12200 --- [nio-9055-exec-2] 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.RuntimeException] with root cause

java.lang.RuntimeException: null
    at com.control.CredentialControl.setup(CredentialControl.java:50) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_271]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_271]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_271]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_271]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1060) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:962) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) ~[tomcat-embed-core-9.0.41.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.41.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.3.jar:5.3.3]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.3.jar:5.3.3]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.3.jar:5.3.3]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:888) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1597) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_271]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_271]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.41.jar:9.0.41]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_271]

I modified CredentialControl to help demonstrate what is happening as well. — Jack J, Feb 07 '21 at 19:38
So NPE occurrs in NameService.java: on line 19. @Boug is probably correct, and your Service is incorrectly instantiated. — ibecar, Feb 07 '21 at 20:11

Panagiotis Bougioukos · Accepted Answer · 2021-02-07T20:10:37.837

1

You create your service with NameService nameService = new NameService();

If you create it with new keyword then any dependencies will not be available, therefore null pointer exception. You have to autowire that service not create it by your self.

With spring when you autowire, spring will not give you an actual instance of that class but a proxy of your class that will behave the way you have read the documentation that it should behave. If you create it by your own then you don't get a proxy that will behave the way you expect it to. You get an actual instance of that class by your self.

Fix: Just go in your controller and declare as a field

@Autowired
NameService nameService

and then just use it in your method like nameService.findAll(); This solution will work only if your service has already autowired the nameRepository and calls the corresponding methods.

But if I understand well the way you use your service is like you could directly call the repository. If that's the case then I would say that you make your controller directly access that repository and your repository should be like

public interface NameRepository extends JpaRepository<Name, Long> { }

And then in your controller just make

    @Autowired
    NameRepository nameRepository

and then just use it in your method like

nameRepository.findAll() instead of nameService.findAll()

edited Feb 07 '21 at 20:10

answered Feb 07 '21 at 19:54

Panagiotis Bougioukos

15,955
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You pointed out the problem. Thank you for that. Instead of following your suggestions though, I created a new control class named SetupControl where I moved the setup method I posted above. Here I Autowired both service classes. I now have a new issue though. The way I have used the setup method, it will save both a Name and a Credential, but it will not update the join table. Do I need to make dao/service classes for the join table as well and fire off all three in the setup method? – Jack J Feb 07 '21 at 21:36
I believe I found the answer to my above issue. What I needed to do was replace `@OneToOne(mappedBy = "credential")` in the Credential entity with the lengthy `@JoinTable` annotation from the Name entity so that the `@JoinTable` code exists in both entities. https://stackoverflow.com/questions/5107330/cascade-type-all-not-working – Jack J Feb 08 '21 at 01:01
OneToOne creates a foreign key column in one table that points to the other table. JoinTable will create another table with foreign keys for joining those 2 tables. It's up to you – Panagiotis Bougioukos Feb 08 '21 at 07:46
keep in mind that according to documentation JoinTable should be used with OneToMany, ManyToOne or ManyToMany – Panagiotis Bougioukos Feb 08 '21 at 07:50

JoinTable annotation causes NullPointerException

Name Entity

Credential Entity

CredentialControl

Stacktrace

1 Answers1