java - 无法使用 @Autowired/WebApplicationContext.getBean() 获取 Bean

Question

我对 Spring 还很陌生，这段代码基于不同的教程，因此请在继续阅读时记住这一点。

这就是任务:

我正在使用 SpringMVC 在现有 Web 服务之上创建一个 Web 前端，该服务在 Websphere Application Server 8.5.5 上运行。

前端只是显示一些数据库表，没什么花哨的。

我尝试使用 WebapplicationContext.getBean() 方法，结果 Controller 出现 org.springframework.beans.factory.BeanCreationException 。其原因是我尝试 Autowiring bean 的行中出现 java.lang.NullPointerException。

因此我在 Stackoverflow 和 google 上搜索有类似问题的人，但找不到任何合适的帖子。

这是我的类(class)。

@ComponenScan 类

@Configuration
@ComponentScan(basePackages= {"com.xyz.webservice.services", "com.xyz.webservice.web"})
public class AppConfig {
}

Controller

@Controller
public class IndexController {
    @Autowired //this works fine
    private WebApplicationContext ctx;

//--> the error
    /* this doesn't work
    @Autowired
    private GridService gs;
    */
    //neither does this work
    private GridService gs = (GridService) ctx.getBean("gridService");
//<--


    @RequestMapping(value= {"", "/", "/index"}, method=RequestMethod.GET)
    public ModelAndView showIndex(ModelAndView mv,
            HttpSession session) {
        Grid grid = getGrid();

        ...

        return mv;
    }

    private Grid getGrid() {
        return (Grid) ctx.getBean("grid"); //this works totally fine
    }
    ...
}

服务

package com.xyz.webservice.services;

@Service
@Scope(value = WebApplicationContext.SCOPE_SESSION, proxyMode = ScopedProxyMode.TARGET_CLASS)
public class GridService {
    ...
}

POJO

package com.xyz.webservice.web;

@Component
@Scope(value = WebApplicationContext.SCOPE_SESSION, proxyMode = ScopedProxyMode.TARGET_CLASS)
public class Grid {
    private List<String> columnNames;
    private List<Page> pages;
    private int currentPageNumber;
    private CrmEmsHistoryProperties sortedBy;
    private boolean isSortedDescending;

    //Getters and Setters

GridService 提供了使用网格的方法。因此， Controller 注入(inject)了网格(通过使用 ctx.getBean("grid");)(它可以正常工作)和 GridService(它根本不起作用)。

预期结果: Controller 应该能够从 Spring 的 IoC-Container 注入(inject) GridService。

实际结果: Controller 无法从 Spring 的 IoC-Container 注入(inject) GridService。

WebApplicationContext.getBean() 抛出此异常:

[8/13/19 12:23:17:785 CEST] 0000008b ServletWrappe E com.ibm.ws.webcontainer.servlet.ServletWrapper init SRVE0271E: Uncaught init() exception created by servlet [dispatcher] in application [WebserviceEAR]: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'indexController': Unsatisfied dependency expressed through field 'gs'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.xyz.webservice.services.GridService' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:588)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:366)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1264)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:668)
at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:540)
at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:494)
at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:171)
at javax.servlet.GenericServlet.init(GenericServlet.java:161)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.init(ServletWrapper.java:345)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.init(ServletWrapperImpl.java:168)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:637)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:481)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:178)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:1114)
at com.ibm.ws.webcontainer.webapp.WebApp.handleRequest(WebApp.java:4047)
at com.ibm.ws.webcontainer.webapp.WebGroup.handleRequest(WebGroup.java:304)
at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:1016)
at com.ibm.ws.webcontainer.WSWebContainer.handleRequest(WSWebContainer.java:1817)
at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:213)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:463)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewRequest(HttpInboundLink.java:530)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.processRequest(HttpInboundLink.java:316)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.ready(HttpInboundLink.java:287)
at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.sendToDiscriminators(NewConnectionInitialReadCallback.java:214)
at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.complete(NewConnectionInitialReadCallback.java:113)
at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:175)
at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:204)
at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:775)
at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:905)
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1892)

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.xyz.webservice.services.GridService' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1493)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1104)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:585)
... 42 more

@Autowire 抛出此异常:

[8/13/19 12:14:35:106 CEST] 00000086 ServletWrappe E com.ibm.ws.webcontainer.servlet.ServletWrapper init SRVE0271E: Uncaught init() exception created by servlet [dispatcher] in application [WebserviceEAR]: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'indexController' defined in file [/home/abc/Repositories/JEE/.metadata/.plugins/org.eclipse.wst.server.core/tmp1/Webservice/WEB-INF/classes/com/xyz/webservice/controller/IndexController.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.xyz.webservice.controller.IndexController]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1155)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1099)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:668)
at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:540)
at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:494)
at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:171)
at javax.servlet.GenericServlet.init(GenericServlet.java:161)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.init(ServletWrapper.java:345)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.init(ServletWrapperImpl.java:168)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.load(ServletWrapper.java:1378)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:1027)
at com.ibm.ws.webcontainer.servlet.CacheServletWrapper.handleRequest(CacheServletWrapper.java:87)
at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:949)
at com.ibm.ws.webcontainer.WSWebContainer.handleRequest(WSWebContainer.java:1817)
at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:213)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:463)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewRequest(HttpInboundLink.java:530)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.processRequest(HttpInboundLink.java:316)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.ready(HttpInboundLink.java:287)
at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.sendToDiscriminators(NewConnectionInitialReadCallback.java:214)
at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.complete(NewConnectionInitialReadCallback.java:113)
at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:175)
at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:204)
at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:775)
at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:905)
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1892)

Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.xyz.webservice.controller.IndexController]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:154)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1147)
... 37 more

Caused by: java.lang.NullPointerException
at com.xyz.webservice.controller.IndexController.<init>(IndexController.java:24)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:83)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:57)
at java.lang.reflect.Constructor.newInstance(Constructor.java:437)
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:142)
... 39 more

希望有人能帮我解决这个问题。

Answer 1

这不起作用，因为在 Bean 生命周期构造中发生在依赖项注入(inject)之前，因此在 gs 初始化时 ctx 尚未注入(inject)并且等于空

private GridService gs = (GridService) ctx.getBean("gridService");

相反，你应该按照以下方式进行

private GridService gs;

@PostConstruct
private void init() {
     gs = (GridService) ctx.getBean("gridService");
}

方法将在所有注入(inject)后调用，因此 gs 的初始化将正确发生。