来自@component、@service e.t.c 注释类的@Autowired 字段为空

Question

我正在尝试使用@AnnotationDrivenConfig。目前，@component、@service e.t.c 注释类中的 @Autowired 字段为空。 Maven 似乎无法为我的项目解析 @AnnotationDrivenConfig 依赖项。通常会在 spring xml 中处理这个问题。对于 Spring 4.1.5 的 java 配置设置，我该如何解决这个问题？

这是堆栈跟踪：

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)

代码如下：

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() );
    }

    /* ... */
}

Answer 1

对于要被 Spring 注入的对象，它必须是 Spring bean。替换

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

通过

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();
}