Question

我编写了一个ViewScoped Managed-Bean，每当我在webbrowser中刷新页面时，Managed-Bean似乎都被重新创建，文章为null，它会加载一个新的文章对象，等等。对我而言，它看起来与RequestScoped的行为相同。

我将Eclipse IDE用于Java EE开发人员，最新的JDK，Apache Tomcat 7.0.8和Mojarra 2.0.3。

有什么问题？

托管bean：

...
import javax.annotation.PostConstruct;
import javax.faces.application.FacesMessage;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;
import javax.faces.bean.ViewScoped;
import javax.faces.context.FacesContext;
...
@ManagedBean
@ViewScoped
public class CreateArticle {

    @ManagedProperty(value = "#{index.facade}")
    private PersistenceFacade facade;
    private Article article;
    private Vector<ArtCategory> artcat;

    public CreateArticle() {
        artcat = ArtCategory.listArtCat();
    }

    @PostConstruct
    public void postCreateArticle() {
        if (article == null) {
            try {
                article = facade.createArticle();
            } catch (DAOException e) {
                e.printStackTrace();
            }
        }
    }

    public void setFacade(PersistenceFacade facade) {
        this.facade = facade;
    }

    public Vector<ArtCategory> getArtcat() {
        return artcat;
    }

    public Article getArticle() {
        return article;
    }

    public String save() {
        try {
            facade.save(article);
            facade.commit();
        } catch (DAOException e) {
            e.printStackTrace();
        }
        FacesMessage message = new FacesMessage(
                "Successful!");
        FacesContext.getCurrentInstance().addMessage(null, message);
        return "/testpage.xhtml";
    }

}

createArticle.xhtml：

<?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">
<h:head>
    <title>Create article</title>
</h:head>
<h:body>
    <h1>
        <h:outputText value="System" />
    </h1>
    <h2>
        <h:outputText value="Test1" />
    </h2>
    <h3>
        <h:outputText value="Test2" />
    </h3>
    <h:form>
        <h:panelGrid columns="3">
            <h:outputLabel for="artname">Articlename</h:outputLabel>
            <h:inputText id="artname" value="#{createArticle.article.artname}"
                required="true">
                <f:ajax event="blur" render="artnameMessage" />
            </h:inputText>
            <h:message id="artnameMessage" for="artname" />

            <h:outputLabel for="briefdesc">Brief description</h:outputLabel>
            <h:inputTextarea id="briefdesc"
                value="#{createArticle.article.briefdesc}" required="false">
                <f:ajax event="blur" render="briefdescMessage" />
            </h:inputTextarea>
            <h:message id="briefdescMessage" for="briefdesc" />

            <h:outputLabel for="price">Price</h:outputLabel>
            <h:inputText id="price" value="#{createArticle.article.price}"
                required="true">
                <f:ajax event="blur" render="priceMessage" />
            </h:inputText>
            <h:message id="priceMessage" for="price" />

            <h:outputLabel for="selectartcat">Article Category</h:outputLabel>
            <h:selectOneMenu id="selectartcat"
                value="#{createArticle.article.artcatnr}" required="true">
                <f:selectItems value="#{createArticle.artcat}" var="artcat"
                    itemLabel="#{artcat.name}" itemValue="#{artcat.artcatnr}" />
                <f:ajax event="blur" render="selectartcatMessage" />
            </h:selectOneMenu>
            <h:message id="selectartcatMessage" for="selectartcat" />

            <h:panelGroup />
            <h:commandButton value="Save"
                action="#{createArticle.save}">
                <f:ajax execute="@form" render="@form" />
            </h:commandButton>
            <h:messages globalOnly="true" layout="table" />
        </h:panelGrid>
    </h:form>
</h:body>
</html>

Answer 1

这是预期的行为。当你通过在浏览器中刷新页面来解雇全新的HTTP GET请求时，它肯定会被重新创建。否则它会像会话范围的bean一样，它会使视图范围无用（想想不同浏览器选项卡中的新GET请求！）。但是，当您调用任何ajax请求或在同一视图中提交表单时，它将 not 重新创建。每次都会重新创建一个请求范围的请求。这是视图范围bean的核心点/优势。

Answer 2

还要确保在ViewScoped bean上实现Serializable，就像使用SessionScoped bean一样。

ViewScoped就像RequestScoped一样 - 为什么？

2 个答案: