Why is @Autowired null, even if I delcare the field inside a Spring class?

Question

I know that there are a question about this problem and lots of answers. But there still no answer why @Autowired become null, even in Spring classes. This must be a bug?

Here is an example where stockNamesRepository is null and not null.

@Data
@Service 
@Configurable // I have tried with @component as well...not working
public class StocksCrud {

    @Autowired
    private StockNamesRepository stockNamesRepository; // This is null

    private Crud<StockNames> crud; // Vaadin object

    private ArrayList<StockNames> crudData;

    @PostConstruct
    public void init() {
        // Fill the crud
        crudData = new ArrayList<StockNames>();
        for(StockNames stockName: stockNamesRepository.findAll()) {
            crudData.add(new StockNames(stockName.getId(), stockName.getStockName()));
        }

    }

}

This is not null

@Component
public class InitialStartUp implements ApplicationListener<ContextRefreshedEvent> {

    @Autowired
    private StockNamesRepository stockNamesRepository; // Not null

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        System.out.println(stockNamesRepository == null); // FALSE
    }

}

So can someone tell me why Spring Framework have these mysterious behaviour?

Here is the error. The code above is minimal for easy reading.

java.lang.NullPointerException: null
    at se.danielmartensson.jweekstocks.vaadin.ui.crud.StocksCrud.saveStock(StocksCrud.java:83) ~[main/:na]
    at se.danielmartensson.jweekstocks.vaadin.ui.crud.StocksCrud.lambda$new$9b1b5227$1(StocksCrud.java:65) ~[main/:na]
    at com.vaadin.flow.component.crud.Crud.lambda$null$3(Crud.java:215) ~[vaadin-crud-flow-2.1.0.jar:na]
    at java.lang.Iterable.forEach(Iterable.java:75) ~[na:1.8.0_232]
    at com.vaadin.flow.component.crud.Crud.lambda$registerHandlers$9b1b5227$4(Crud.java:215) ~[vaadin-crud-flow-2.1.0.jar:na]
    at com.vaadin.flow.component.ComponentEventBus.fireEventForListener(ComponentEventBus.java:205) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.component.ComponentEventBus.handleDomEvent(ComponentEventBus.java:373) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.component.ComponentEventBus.lambda$addDomTrigger$dd1b7957$1(ComponentEventBus.java:264) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.internal.nodefeature.ElementListenerMap.lambda$fireEvent$2(ElementListenerMap.java:441) ~[flow-server-2.1.2.jar:2.1.2]
    at java.util.ArrayList.forEach(ArrayList.java:1257) ~[na:1.8.0_232]
    at com.vaadin.flow.internal.nodefeature.ElementListenerMap.fireEvent(ElementListenerMap.java:441) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.server.communication.rpc.EventRpcHandler.handleNode(EventRpcHandler.java:59) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.server.communication.rpc.AbstractRpcInvocationHandler.handle(AbstractRpcInvocationHandler.java:64) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.server.communication.ServerRpcHandler.handleInvocationData(ServerRpcHandler.java:400) [flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.server.communication.ServerRpcHandler.lambda$handleInvocations$1(ServerRpcHandler.java:381) [flow-server-2.1.2.jar:2.1.2]
    at java.util.ArrayList.forEach(ArrayList.java:1257) ~[na:1.8.0_232]
    at com.vaadin.flow.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:381) [flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:316) [flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:89) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.server.VaadinService.handleRequest(VaadinService.java:1540) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.server.VaadinServlet.service(VaadinServlet.java:247) ~[flow-server-2.1.2.jar:2.1.2]
    at com.vaadin.flow.spring.SpringServlet.service(SpringServlet.java:95) ~[vaadin-spring-12.1.2.jar:na]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:352) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.servlet.mvc.ServletForwardingController.handleRequestInternal(ServletForwardingController.java:141) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:177) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:52) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:320) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:118) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:158) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:92) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:77) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:215) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:178) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:358) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:271) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1591) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) ~[na:1.8.0_232]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) ~[na:1.8.0_232]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_232]

Update:

This is how I inject StockCrud class

@Route("")
@Push
@Viewport("width=device-width, minimum-scale=1, initial-scale=1, user-scalable=yes, viewport-fit=cover")
@PWA(name = "My Application", shortName = "My App")
public class MainView extends AppLayout {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private WeeksGrid weeksGrid;
    private StocksCrud stocksCrud;

    @PostConstruct
    public void init() {

        weeksGrid = new WeeksGrid();
        stocksCrud = new StocksCrud();
    }

}

Please show the stack trace, as well as the point where you inject the `StocksCrud`. — Turing85, Jan 11 '20 at 23:27
Is annotation driven injection enabled? also are they in same package? — Volkan Albayrak, Jan 11 '20 at 23:31
@VolkanAlbayrak I don't know what you mean. They are not in the same package. Different classes. — euraad, Jan 11 '20 at 23:32
@DanielMårtensson again, please show where you inject the `StocksCrud` or the code how you create the `StocksCrud`. — Turing85, Jan 11 '20 at 23:33
Does this answer your question? [Why is my Spring @Autowired field null?](https://stackoverflow.com/questions/19896870/why-is-my-spring-autowired-field-null) — Sebastian Brudzinski, Jan 12 '20 at 00:41

Turing85 · Accepted Answer · 2020-02-24T22:53:07.680

You are not creating the instance of StocksCrud through the DI containter, thus spring is not able to inject any dependencies. Inject the StocksCrud into MainView and it should get properly initialized.

Some explanation: In order for Spring (or any DI container, really) to work its magic, the container needs to create the bean in question. In the code presented, the instance of StocksCrud is created through new, i.e. not through the DI container. The use of a DI container does not change the semantics of Java, thus new StocksCrud() has the same semantics as in any Java-program. The DI-containers analyze annotated beans to check for certain annotations (e.g. @Inject or @Autowired) and tries to inject other fitting beans as dependencies.

A comment on your code: Instead of field injection, I would strongly suggest using constructor injection.

That's right! I need to put @autowired inside the MainView and add the repository as argument for `StocksCrud` class.!! That solved my problem. — euraad, Jan 12 '20 at 12:44

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

1

According to the documentation, you should enable autowired with following line.

Enabling @Autowired Annotations

If you are using Java based configuration in your application you can enable annotation-driven injection by using AnnotationConfigApplicationContext to load your spring configuration as below:


@Configuration
@ComponentScan("com.baeldung.autowire.sample")
public class AppConfig {}

https://www.baeldung.com/spring-autowire

edited Jun 20 '20 at 09:12

Community

1
1

answered Jan 11 '20 at 23:44

Volkan Albayrak

329
1
11

OP showed that the annotation did work in a different case. Thus, java-based configuration is working. The probiem is that OP creates the `StocksCrud` via `new` and not use the DI container to inject it. – Turing85 Jan 11 '20 at 23:47
@Turing85 I suppose InitialStartup class which is working, is on same package with main class. But for spring to discover all components, we need to add componentscan – Volkan Albayrak Jan 12 '20 at 00:14
Depends on the exact package structure. If `MainView` is in a sub-package of the package the `@Application` resides in, Spring will pick it up automatically. – Turing85 Jan 12 '20 at 00:16
Exactly! Thats what I mean. I guess not working class is in different package. This is the first question that I asked. – Volkan Albayrak Jan 12 '20 at 00:18

Why is @Autowired null, even if I delcare the field inside a Spring class?

2 Answers2