为什么我的@Autowired 对象为空? [英] Why is my @Autowired object null?
问题描述
我有以下 JSF 托管 bean:
I've the below JSF managed bean:
package com.example;
import java.io.Serializable;
import javax.faces.bean.ManagedBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
@Component
@ManagedBean
public class Bean implements Serializable {
@Autowired
private SomeService someService;
public void update() {
someService.update(someEntity);
}
// ...
}
以及下面的 Spring 服务:
And the below Spring service:
@Transactional
@Repository
public class SomeService {
@Autowired
private SessionFactory sessionFactory;
// ...
}
Spring 配置如下:
Spring is configured as below:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<description>Example configuration to get you started.</description>
<context:component-scan base-package="com.example" />
<!-- To add exception translation to a template-less Hibernate DAO -->
<bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor" />
<context:annotation-config />
<!-- Database Configuration -->
<import resource="database/DataSource.xml" />
<import resource="database/Hibernate.xml" />
<tx:annotation-driven />
</beans>
当我调用 JSF 托管 bean update() 方法时，它抛出一个 NullPointerException:
When I call the JSF managed bean update() method, it throws a NullPointerException:
javax.faces.FacesException: #{bean.update()}: java.lang.NullPointerException
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:117)
at org.springframework.faces.webflow.FlowActionListener.processAction(FlowActionListener.java:71)
at org.springframework.faces.model.SelectionTrackingActionListener.processAction(SelectionTrackingActionListener.java:55)
at javax.faces.component.UICommand.broadcast(UICommand.java:315)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:786)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1251)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.ocpsoft.rewrite.servlet.RewriteFilter.doFilter(RewriteFilter.java:191)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)
Caused by: javax.faces.el.EvaluationException: java.lang.NullPointerException
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:101)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:101)
... 28 more
Caused by: java.lang.NullPointerException
at com.example.Bean.update(Bean.java:45)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.apache.el.parser.AstValue.invoke(AstValue.java:278)
at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:274)
at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:87)
... 29 more
换句话说，someService 是 null.我终其一生都无法弄清楚原因.我在 bean 的顶部声明了 @Component.所以我希望 @Autowired 能够正常工作.任何帮助都会很棒！
In other words, someService is null. I cannot for the life of me figure out why. I have @Component declared at the top of my bean. So I expect @Autowired to just work. Any help will be great!
推荐答案
您不能像这里尝试的那样混合注释和上下文.
You cannot mix annotations and contexts like you're attempting here.
首先，要将 Spring bean(或实际上，任何 bean)注入 JSF 托管 bean，请使用 @ManagedProperty 批注.因此，如果其他一切设置正确(Spring 方面，包括 Spring Faces EL 解析器)，您应该:
First, to inject a Spring bean (or really, any bean) into a JSF managed bean, use the @ManagedProperty annotation. So, if everything else is setup properly (Spring-wise, including the Spring Faces EL resolver), you should have:
@ManagedProperty("#{someService}")
private SomeService someService;
当您将类声明为 @ManagedBean 时，它在 Spring 的上下文之外.结果，@Autowired 在这里没有权力；spring 不能将任何内容注入其上下文之外的任何内容.
When you declare a class as a @ManagedBean, it's outside the context of Spring. As a result, @Autowired has no power here; spring cannot inject anything into anything that's outside of its context.
如果要使用@Component和@Autowired这对，需要去掉@ManagedBean，使其成为Spring托管 bean 而不是 JSF 托管 bean.
If you want to use the pair of @Component and @Autowired, you need to remove @ManagedBean so that it becomes a Spring managed bean instead of a JSF managed bean.
这篇关于为什么我的@Autowired 对象为空?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
