@ViewScoped Managed bean loads many times during postback

问题

I have a calendar, editor, fileUpload and a dataTable primefaces controls on a jsf facelet.

Code is as follows,

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

    <ui:define name="title">#{lbl.SSTitle}</ui:define>

    <ui:define name="content">
        <h:form>
            <p:panel header="Upload Script">
                <h:outputText value="Welcome #{loginActionBean.login.emp.empName}"/>
                <br />
                <p:calendar value="#{searchScriptActionBean.scheduleDate}" />
                <br />
                <p:fileUpload fileUploadListener="#{searchScriptActionBean.handleFileUpload}"
                              multiple="true" update="filsList" allowTypes="*.txt;*.init" description="Script Files">
                </p:fileUpload>
                <br />
                <p:editor value="#{searchScriptActionBean.htmlText}" />
            </p:panel>
            <p:dataTable id="filsList" value="#{searchScriptActionBean.scriptFiles}" var="file">

                <p:column>
                    <f:facet name="header">
                        <h:outputText value="File Name" />
                    </f:facet>
                    <h:outputText value="#{file.fileName}" />
                </p:column>

                <p:column>
                    <f:facet name="header">
                        <h:outputText value="Size" />
                    </f:facet>
                    <h:outputText value="#{file.size}" />
                </p:column>

                <p:column>
                    <f:facet name="header">
                        <h:outputText value="Operation" />
                    </f:facet>
                    <h:commandLink value="Remove">
                        <p:collector value="#{file}" removeFrom="#{searchScriptActionBean.scriptFiles}" />
                    </h:commandLink>
                </p:column>

            </p:dataTable>
        </h:form>
    </ui:define>
</ui:composition>

and @ViewScoped Bean as follows,

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package com.ugam.crawler.web.script;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import javax.faces.bean.ViewScoped;
import javax.inject.Named;
import org.primefaces.event.FileUploadEvent;
import org.primefaces.model.UploadedFile;

/**
 *
 * @author devendra.mahajan
 */
@Named(value = "searchScriptActionBean")
@ViewScoped
public class SearchScriptActionBean implements Serializable{

    protected String htmlText;
    private Date scheduleDate;
    private List<UploadedFile> scriptFiles = new ArrayList<UploadedFile>();;
    /**
     * Get the value of scheduleDate
     *
     * @return the value of scheduleDate
     */
    public Date getScheduleDate() {
        return scheduleDate;
    }

    /**
     * Set the value of scheduleDate
     *
     * @param scheduleDate new value of scheduleDate
     */
    public void setScheduleDate(Date scheduleDate) {
        this.scheduleDate = scheduleDate;
    }

    /**
     * @return the scriptFiles
     */
    public List<UploadedFile> getScriptFiles() {
        return scriptFiles;
    }

    /**
     * @param scriptFiles the scriptFiles to set
     */
    public void setScriptFiles(List<UploadedFile> scriptFiles) {
        this.scriptFiles = scriptFiles;
    }

    /** Creates a new instance of SearchScriptActionBean */
    public SearchScriptActionBean() {
        System.out.println("In SearchScriptActionBean Constructor");

    }

    public void handleFileUpload(FileUploadEvent event) {
        //add facesmessage to display with growl
        //application code
        UploadedFile file = event.getFile();
        scriptFiles.add(file);


    }


    /**
     * Get the value of htmlText
     *
     * @return the value of htmlText
     */
    public String getHtmlText() {
        return htmlText;
    }

    /**
     * Set the value of htmlText
     *
     * @param htmlText new value of htmlText
     */
    public void setHtmlText(String htmlText) {
        this.htmlText = htmlText;
    }
}

My Problem is SearchScriptActionBean loads many time when the form loads and when a file is uploaded. I want to retain old values of bean. ex. scriptFiles(List), where uploaded files are added. and filsList (dataTable) is not getting updated.

回答1:

Look much like issue 1492. Here's a cite of relevance:

This is a chicken/egg issue with partial state saving. The view is executed to populate the view before delta state is applied, so we see the behavior you've described.

At this point, I don't see a clear way to resolve this use case.

The workaround, if you must use view-scoped bindings would be setting javax.faces.PARTIAL_STATE_SAVING to false.

Probably Primefaces is implicitly binding the uploaded file with the view and you need to add the following to the web.xml:

<context-param>
    <param-name>javax.faces.PARTIAL_STATE_SAVING</param-name>
    <param-value>false</param-value>
</context-param>

Give it a try and see if that helps. If it works, you may want to consider to turn if off for a specific view only. Globally turning off partial state saving will namely noticeably increase memory and/or bandwidth usage, depending on state saving method. Assuming that the view ID is /upload.xhtml, use this:

<context-param>
    <param-name>javax.faces.FULL_STATE_SAVING_VIEW_IDS</param-name>
    <param-value>/upload.xhtml</param-value>
</context-param>

You can specify multiple view IDs by a semicolon.

来源：https://stackoverflow.com/questions/3256142/viewscoped-managed-bean-loads-many-times-during-postback