@Autowired fields from @component, @service e.t.c annotated classes are null

Question

I am trying to use the @AnnotationDrivenConfig. At the moment, my @Autowired fields from @component, @service e.t.c annotated classes are null. Maven does not seem to be able to resolve the @AnnotationDrivenConfig dependencies for my project. would usually take care of this in the spring xml. How can I solve this problem for a java config set-up with Spring 4.1.5?

Here is the stack trace:

DEBUG: org.springframework.web.servlet.DispatcherServlet - Handler execution resulted in exception java.lang.NullPointerException
at com.reviewsystem.crazytenants.application.controllers.interceptors.SiteSwitcher.preHandle(MySwitcher.java:23)
at org.springframework.web.servlet.HandlerExecutionChain.applyPreHandle(HandlerExecutionChain.java:134)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:217)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)

Here is the code:

MySwitcher.java

package x.y.z

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

import x.y.z.MySwitcherHandler;

@Component
public class MySwitcher extends HandlerInterceptorAdapter {

    public MySwitcher(){
        super();
    }

    public boolean preHandle( HttpServletRequest request, HttpServletResponse response, Object handler ) throws Exception {
        mySwitcherHandler.setup( request, response );
        return true;
    }

    @Autowired
    private MySwitcherHandler mySwitcherHandler;
}

MySwitcherHandler.java

package x.y.z

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.mobile.device.Device;
import org.springframework.mobile.device.site.SitePreference;
import org.springframework.stereotype.Service;

@Service
public class MySwitcherHandler {

    public MySwitcherHandler(){}

    public MySwitcherHandler( HttpServletRequest request, HttpServletResponse response ){
        setup( request, response );
    }

    public void setup( HttpServletRequest request, HttpServletResponse response ){
        System.out.println( "running MySiteSwitcherHandler.setup( HttpServletRequest request, HttpServletResponse response )" );    
    }

    public void setup( SitePreference sitePreference, Device device ){
        System.out.println( "running MySiteSwitcherHandler.setup( SitePreference sitePreference, Device device )" );
    }

    public void update( SitePreference sitePreference, Device device ){
        System.out.println( "running MySiteSwitcherHandler.update( SitePreference sitePreference, Device device )" );
    }
}

AppConfig.java

package x.y.z;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.web.servlet.config.annotation.DefaultServletHandlerConfigurer;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

//@AnnotationDrivenConfig
@ComponentScan( basePackages = {"x.y.z."} )
@Configuration
@EnableWebMvc
public class AppConfig extends WebMvcConfigurerAdapter {

    @Override
    public void configureDefaultServletHandling( DefaultServletHandlerConfigurer configurer ) {
        configurer.enable();
    }

    @Bean 
    public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
        return new PropertySourcesPlaceholderConfigurer();
    }

    @Override
    public void addArgumentResolvers( List<HandlerMethodArgumentResolver> argumentResolvers ) {
        argumentResolvers.add( new ServletWebArgumentResolverAdapter( new DeviceWebArgumentResolver() ));
        argumentResolvers.add( new ServletWebArgumentResolverAdapter( new SitePreferenceWebArgumentResolver() ));
    }

    @Override
    public void addInterceptors( InterceptorRegistry registry ) {
        registry.addInterceptor( new DeviceResolverHandlerInterceptor() );
        registry.addInterceptor( new SitePreferenceHandlerInterceptor() );
        registry.addInterceptor( new MySwitcher() );
    }

    /* ... */
}

@Chrylis, I have now also added stack trace and code. Thanks — Stephen Isienyi, Nov 01 '15 at 17:32
Duplicate of [this](http://stackoverflow.com/questions/19896870/why-is-my-spring-autowired-field-null). — Sotirios Delimanolis, Nov 01 '15 at 18:50
The issue in your proposed duplicate link was because the MileageFeeController.mileageFee method has a MileageFeeCalculator variable that was declared out of Spring IOC container. Please take additional look. Thanks — Stephen Isienyi, Nov 01 '15 at 22:19
@APC many thanks for providing additional editing to the question — Stephen Isienyi, Nov 01 '15 at 22:22

score 1 · Accepted Answer · answered Nov 07 '15 at 08:03

For an object to be injected by Spring, it must be a Spring bean. Replace

@Override
public void addInterceptors( InterceptorRegistry registry ) {
    registry.addInterceptor( new DeviceResolverHandlerInterceptor() );
    registry.addInterceptor( new SitePreferenceHandlerInterceptor() );
    registry.addInterceptor( new MySwitcher() );
}

by

public void addInterceptors(InterceptorRegistry registry) {
    registry.addInterceptor(deviceResolverHandlerInterceptor());
    registry.addInterceptor(sitePreferenceHandlerInterceptor());
    registry.addInterceptor(mySwitcher());
}

@Bean
public DeviceResolverHandlerInterceptor deviceResolverHandlerInterceptor() {
    return new DeviceResolverHandlerInterceptor();
}

@Bean
public SitePreferenceHandlerInterceptor sitePreferenceHandlerInterceptor() {
    return new SitePreferenceHandlerInterceptor();
}

@Bean
public MySwitcher mySwitcher() {
    return new MySwitcher();
}

Thank you, @JB Nizet. This was quite helpful. I ended up adding to my AppConfig class an autowired private SiteSwitcher siteSwitcher field and removed the instantiated SiteSwitcher argument. — Stephen Isienyi, Nov 07 '15 at 22:24

@Autowired fields from @component, @service e.t.c annotated classes are null

1 Answers1