Question

我在JSF页面中使用此代码

<h:outputText value="#{writeBean.t}" />

（我在WEB-INF文件夹中有一个beans.xml）

这是写入后一个StringBean的WriteBean：

package huhu.main.managebean;

import java.io.Serializable;
import javax.enterprise.context.SessionScoped;
import javax.enterprise.inject.Default;
import javax.inject.Inject;
import javax.inject.Named;


@Default
@Named
@SessionScoped
public class WriteBean implements Serializable {
   /**
 * 
 */
private static final long serialVersionUID = 1L;

String t;

@Inject StringBean stringbean;


public WriteBean() {
  setT(stringbean.getS());
}

public String getT() {
  return t;
}

public void setT(String t) {
  this.t = t;
}
}

这是StringBean，其中设置了我想在JSF页面上显示的字符串：

package huhu.main.managebean;

import java.io.Serializable;
import javax.enterprise.context.SessionScoped;
import javax.enterprise.inject.Default;
import javax.inject.Named;

@Default
@Named
@SessionScoped
public class StringBean implements Serializable {

   /**
* 
*/
   private static final long serialVersionUID = 1L;

   String s = new String("WORKS!!");

   public StringBean(){

   }

   public String getS() {
     return s;
   }

   public void setS(String s) {
  this.s = s;
  }
}

这是例外：

    HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: java.lang.RuntimeException: java.lang.NullPointerException
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:606)
    org.jboss.weld.servlet.ConversationPropagationFilter.doFilter(ConversationPropagationFilter.java:62)
root cause

com.google.common.collect.ComputationException: java.lang.RuntimeException: java.lang.NullPointerException
    com.google.common.collect.ComputingConcurrentHashMap$ComputingMapAdapter.get(ComputingConcurrentHashMap.java:397)
    org.jboss.weld.bean.proxy.ClientProxyProvider.getClientProxy(ClientProxyProvider.java:102)
    org.jboss.weld.el.AbstractWeldELResolver.lookup(AbstractWeldELResolver.java:115)
    org.jboss.weld.el.AbstractWeldELResolver.getValue(AbstractWeldELResolver.java:96)
    org.jboss.as.weld.webtier.jsf.ForwardingELResolver.getValue(ForwardingELResolver.java:46)
    javax.el.CompositeELResolver.getValue(CompositeELResolver.java:175)
    com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
    com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
    org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:72)
    org.apache.el.parser.AstValue.getValue(AstValue.java:147)
    org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
    org.jboss.weld.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
    com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
    javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
    javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
    javax.faces.component.UIOutput.getValue(UIOutput.java:169)
    com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:205)
    com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:355)
    com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
    javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1786)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:402)
    com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:125)
    javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:288)
    com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121)
    com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
    org.jboss.weld.servlet.ConversationPropagationFilter.doFilter(ConversationPropagationFilter.java:62)
root cause

java.lang.RuntimeException: java.lang.NullPointerException
    org.jboss.weld.util.reflection.SecureReflectionAccess.runAsInstantiation(SecureReflectionAccess.java:186)
    org.jboss.weld.util.reflection.SecureReflections.newInstance(SecureReflections.java:340)
    org.jboss.weld.bean.proxy.ProxyFactory.create(ProxyFactory.java:240)
    org.jboss.weld.bean.proxy.ClientProxyProvider.createClientProxy(ClientProxyProvider.java:87)
    org.jboss.weld.bean.proxy.ClientProxyProvider.access$000(ClientProxyProvider.java:43)
    org.jboss.weld.bean.proxy.ClientProxyProvider$1.apply(ClientProxyProvider.java:53)
    org.jboss.weld.bean.proxy.ClientProxyProvider$1.apply(ClientProxyProvider.java:46)
    com.google.common.collect.ComputingConcurrentHashMap$ComputingValueReference.compute(ComputingConcurrentHashMap.java:355)
    com.google.common.collect.ComputingConcurrentHashMap$ComputingSegment.compute(ComputingConcurrentHashMap.java:184)
    com.google.common.collect.ComputingConcurrentHashMap$ComputingSegment.getOrCompute(ComputingConcurrentHashMap.java:153)
    com.google.common.collect.ComputingConcurrentHashMap.getOrCompute(ComputingConcurrentHashMap.java:69)
    com.google.common.collect.ComputingConcurrentHashMap$ComputingMapAdapter.get(ComputingConcurrentHashMap.java:393)
    org.jboss.weld.bean.proxy.ClientProxyProvider.getClientProxy(ClientProxyProvider.java:102)
    org.jboss.weld.el.AbstractWeldELResolver.lookup(AbstractWeldELResolver.java:115)
    org.jboss.weld.el.AbstractWeldELResolver.getValue(AbstractWeldELResolver.java:96)
    org.jboss.as.weld.webtier.jsf.ForwardingELResolver.getValue(ForwardingELResolver.java:46)
    javax.el.CompositeELResolver.getValue(CompositeELResolver.java:175)
    com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
    com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
    org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:72)
    org.apache.el.parser.AstValue.getValue(AstValue.java:147)
    org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
    org.jboss.weld.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
    com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
    javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
    javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
    javax.faces.component.UIOutput.getValue(UIOutput.java:169)
    com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:205)
    com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:355)
    com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
    javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1786)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:402)
    com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:125)
    javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:288)
    com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121)
    com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
    org.jboss.weld.servlet.ConversationPropagationFilter.doFilter(ConversationPropagationFilter.java:62)
root cause

java.lang.NullPointerException
    huhu.main.managebean.WriteBean.<init>(WriteBean.java:25)
    huhu.main.managebean.WriteBean$Proxy$_$$_WeldClientProxy.<init>(WriteBean$Proxy$_$$_WeldClientProxy.java)
    sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    java.lang.reflect.Constructor.newInstance(Unknown Source)
    java.lang.Class.newInstance0(Unknown Source)
    java.lang.Class.newInstance(Unknown Source)
    org.jboss.weld.util.reflection.SecureReflections$16.work(SecureReflections.java:343)
    org.jboss.weld.util.reflection.SecureReflectionAccess.run(SecureReflectionAccess.java:52)
    org.jboss.weld.util.reflection.SecureReflectionAccess.runAsInstantiation(SecureReflectionAccess.java:173)
    org.jboss.weld.util.reflection.SecureReflections.newInstance(SecureReflections.java:340)
    org.jboss.weld.bean.proxy.ProxyFactory.create(ProxyFactory.java:240)
    org.jboss.weld.bean.proxy.ClientProxyProvider.createClientProxy(ClientProxyProvider.java:87)
    org.jboss.weld.bean.proxy.ClientProxyProvider.access$000(ClientProxyProvider.java:43)
    org.jboss.weld.bean.proxy.ClientProxyProvider$1.apply(ClientProxyProvider.java:53)
    org.jboss.weld.bean.proxy.ClientProxyProvider$1.apply(ClientProxyProvider.java:46)
    com.google.common.collect.ComputingConcurrentHashMap$ComputingValueReference.compute(ComputingConcurrentHashMap.java:355)
    com.google.common.collect.ComputingConcurrentHashMap$ComputingSegment.compute(ComputingConcurrentHashMap.java:184)
    com.google.common.collect.ComputingConcurrentHashMap$ComputingSegment.getOrCompute(ComputingConcurrentHashMap.java:153)
    com.google.common.collect.ComputingConcurrentHashMap.getOrCompute(ComputingConcurrentHashMap.java:69)
    com.google.common.collect.ComputingConcurrentHashMap$ComputingMapAdapter.get(ComputingConcurrentHashMap.java:393)
    org.jboss.weld.bean.proxy.ClientProxyProvider.getClientProxy(ClientProxyProvider.java:102)
    org.jboss.weld.el.AbstractWeldELResolver.lookup(AbstractWeldELResolver.java:115)
    org.jboss.weld.el.AbstractWeldELResolver.getValue(AbstractWeldELResolver.java:96)
    org.jboss.as.weld.webtier.jsf.ForwardingELResolver.getValue(ForwardingELResolver.java:46)
    javax.el.CompositeELResolver.getValue(CompositeELResolver.java:175)
    com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
    com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
    org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:72)
    org.apache.el.parser.AstValue.getValue(AstValue.java:147)
    org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
    org.jboss.weld.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
    com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
    javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
    javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
    javax.faces.component.UIOutput.getValue(UIOutput.java:169)
    com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:205)
    com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:355)
    com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
    javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1786)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:402)
    com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:125)
    javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:288)
    com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121)
    com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
    org.jboss.weld.servlet.ConversationPropagationFilter.doFilter(ConversationPropagationFilter.java:62)
note The full stack trace of the root cause is available in the JBoss Web/7.0.13.Final logs.

JBoss Web/7.0.13.Final

Answer 1

您只需创建该方法（替换构造函数）：

@PostConstruct
public void init() {
    setT(stringbean.getS());
}

来自javax.annotation.PostConstruct，它将在CDI创建你的bean后立即调用。

Answer 2

我认为我的错误很简单：您无法在构造函数中调用注入的属性，因为它意味着尝试访问尚未设置的属性。现在我只是清空WriteBean构造函数并在新方法writer（）中使用了代码行：

public String writer(){
    setT(stringbean.getS());
    return t;
}

我在jsf页面上调用了一个：

<h:outputText value="#{writeBean.writer()}" />

NullPointerException：使用CDI将值从一个bean传递到另一个bean将不起作用

2 个答案: