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在SelectOneMenu列表中检索所选项目的值

分类: 技术问答 • 2022-06-01 10:50:10
问题描述：

我只想在SelectOneMenu列表
中检索所选用户的登录名，这是代码：

i just want to retrieve the login of the selected User in the SelectOneMenu List here's the code :

我的xhtml页面： 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml"
  xmlns:f="http://java.sun.com/jsf/core"      
  xmlns:h="http://java.sun.com/jsf/html"
  xmlns:ui="http://java.sun.com/jsf/facelets"
  xmlns:p="http://primefaces.org/ui">

<h:head>
    <title>JSF 2.0 Test</title>
</h:head>
<h:body>
    <h3>JSF 2.0 Test</h3>
    <h:form>

    <br></br>
 <p:commandButton id="modalDialogButton" value="Modal" onclick="dlg2.show();"  
     type="button"/>  
<p:dialog id="modalDialog" header="Modal Dialog" widgetVar="dlg2" modal="true" 
     height="100">  
     <h:outputText value="This is a Modal Dialog." />  

      <p:selectOneMenu value="#{adminMB.selectedUser}" converter="userConverter" 
       effect="fade">  
            <f:selectItem itemLabel="Choose Administor" />  
            <f:selectItems value="#{adminMB.users}" var="user" itemValue="#{user}" 
            itemLabel="#{user.userLogin}" />  
       </p:selectOneMenu>  

      <p:commandButton id="Add"  value=" Add "  actionListener="#  
      {adminMB.createProject}"></p:commandButton>

        </p:dialog>  

    </h:form>
</h:body>
 </html>

adminMB.createProject方法： 

 public void createProject(ActionEvent actionEvent){

  System.err.println("created project admin login :"+this.selectedUser.getUserLogin());
                                               }

UserConverter类： 

 package tn.talan.testFramework.converter;

 import java.util.ArrayList;
 import javax.faces.component.UIComponent;
 import javax.faces.context.FacesContext;
 import javax.faces.convert.Converter;
 import javax.faces.convert.FacesConverter;

 import org.objectweb.salome_tmf.data.User;
 import org.objectweb.salome_tmf.ihm.admin.AdministrationFinal;

 import tn.talan.testFramework.managedBean.AdminMB;

 @FacesConverter (value="userConverter")//(forClass= AdminMB.class)

 public class UserConverter implements Converter {

@Override public Object getAsObject(FacesContext context, UIComponent component, 
    String value) {

    User selectedUser = null;
    ArrayList<User>  usersList;
    String userLogin;
    AdministrationFinal  administration=new AdministrationFinal();
    administration.onInit();
    usersList = administration.getAllUsers();
    if (usersList!=null){
    for(int i=0 ;i<usersList.size();i++)
    {   selectedUser=usersList.get(i);
        userLogin=selectedUser.getLoginFromModel();

    System.err.println(userLogin);
    if  (userLogin==value)
        return userLogin;
    }
    }
    return null;
}

 @Override
 public String getAsString(FacesContext context, UIComponent component, Object  value)    
     {
     if (value == null) return ""; 
     return ((User) value).getUserLogin();

 }

   }

所以当我单击添加按钮，将调用AdminMB Bean的createProject方法，并且出现此错误：

So when i click on the "Add" button , the createProject method of the AdminMB Bean is invoked and i'm getting this error :

错误输出： 

26 août 2012 13:58:52 javax.faces.event.MethodExpressionActionListener processAction
GRAVE: Réception de 'java.lang.NullPointerException' lors de l'invocation du listener d'action '#{adminMB.createProject}' du composant 'Add'
26 août 2012 13:58:52 javax.faces.event.MethodExpressionActionListener processAction
GRAVE: java.lang.NullPointerException
    at tn.talan.testFramework.managedBean.AdminMB.createProject(AdminMB.java:205)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.apache.el.parser.AstValue.invoke(AstValue.java:264)
    at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:278)
at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:102)
    at javax.faces.event.MethodExpressionActionListener.processAction(MethodExpressionActionListener.java:144)
    at javax.faces.event.ActionEvent.processListener(ActionEvent.java:84)
    at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:773)
    at javax.faces.component.UICommand.broadcast(UICommand.java:296)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:790)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1255)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:77)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:114)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:334)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    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:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    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:1001)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

26 août 2012 13:58:52 com.sun.faces.context.AjaxExceptionHandlerImpl log
GRAVE: JSF1073 : javax.faces.event.AbortProcessingException intercepté durant le traitement de INVOKE_APPLICATION 5 : UIComponent-ClientId=j_idt8:Add, Message=/primeFacesDialog.xhtml @31,97 actionListener="#{adminMB.createProject}": java.lang.NullPointerException
26 août 2012 13:58:52 com.sun.faces.context.AjaxExceptionHandlerImpl log
GRAVE: /primeFacesDialog.xhtml @31,97 actionListener="#{adminMB.createProject}": java.lang.NullPointerException
javax.faces.event.AbortProcessingException: /primeFacesDialog.xhtml @31,97 actionListener="#{adminMB.createProject}": java.lang.NullPointerException
    at javax.faces.event.MethodExpressionActionListener.processAction(MethodExpressionActionListener.java:178)
    at javax.faces.event.ActionEvent.processListener(ActionEvent.java:84)
    at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:773)
    at javax.faces.component.UICommand.broadcast(UICommand.java:296)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:790)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1255)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:77)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:114)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:334)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    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:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    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:1001)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)


答

如果如您在上面的对话中所暗示的，所选值已成功转换，则下一个罪魁祸首是您的托管bean。具体来说，是受管bean的范围。如果您使用的是 @RequestScoped bean，那么肯定会遇到这样的问题。将您的bean更改为 @ViewScoped 并查看会发生什么情况

If the selected value is being converted successfully as you've implied in your conversation above, the next available culprit is your managed bean. Specifically, the scope of your managed bean. If you're using a @RequestScoped bean, you're certain to run into problems like this. Change your bean to a @ViewScoped and see what happens

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