flash.keep & flash.setKeepMessages(true) 重定向

Question

我正在看 Anghel Leonard 一书中的一个例子 Mastering Java Server Faces 2.2.

作者举例说明了如何在bean创建时为下一次重定向请求保留数据@RequestScoped。

这是 index.xhtml-

的代码

<h:body>
    <f:metadata> 
        <f:event type="preRenderView" 
            listener="#{playersBean.pullValuesFromFlashAction}"/> 
    </f:metadata>
    <h:messages />  
    <h:form>                       
        Name: <h:inputText value="#{playersBean.playerName}"/>
        Surname: <h:inputText value="#{playersBean.playerSurname}"/>
        <h:commandButton value="Register" 
            action="#{playersBean.addValuesToFlashAction()}"/>          
    </h:form>
</h:body>

terms.xhtml-

<h:body>
    <h:messages />  
    Hello, <h:outputText value="#{flash.keep.playerName} #{flash.keep.playerSurname}"/>    
    <br/><br/>Terms &amp; Conditions ... ... ... ... ...
    <h:form>
        <h:commandButton value="Reject" 
            action="#{playersBean.termsRejectedAction()}" />
        <h:commandButton value="Accept" 
            action="#{playersBean.termsAcceptedAction()}" />
    </h:form>
</h:body>

done.xhtml-

<h:head>
    <title></title>
</h:head>   
<h:body>
    <f:metadata> 
        <f:event type="preRenderView" 
            listener="#{playersBean.pullValuesFromFlashAction}"/> 
    </f:metadata>
    <h:messages />  
    <h:outputText value="#{playersBean.playerName} #{playersBean.playerSurname}"/> 
        successfully registered!           
</h:body>

和支持 bean-

@ManagedBean
@RequestScoped
public class PlayersBean {

    private final static Logger logger = Logger.getLogger(PlayersBean.class.getName());
    private String playerName;
    private String playerSurname;
    public PlayersBean() {
    }
    public String getPlayerName() {
        return playerName;
    }
    public void setPlayerName(String playerName) {
        this.playerName = playerName;
    }
    public String getPlayerSurname() {
        return playerSurname;
    }
    public void setPlayerSurname(String playerSurname) {
        this.playerSurname = playerSurname;
    }
    public String addValuesToFlashAction() {

        Flash flash = FacesContext.getCurrentInstance().getExternalContext().getFlash();
        flash.put("playerName", playerName);
        flash.put("playerSurname", playerSurname);
        return "terms?faces-redirect=true";
    }
    public void pullValuesFromFlashAction(ComponentSystemEvent e) {
        Flash flash = FacesContext.getCurrentInstance().getExternalContext().getFlash();
        playerName = (String) flash.get("playerName");
        playerSurname = (String) flash.get("playerSurname");
    }
    public String termsAcceptedAction() {
        Flash flash = FacesContext.getCurrentInstance().getExternalContext().getFlash();

        flash.setKeepMessages(true);
        pullValuesFromFlashAction(null);

        //do something with firstName, lastName 
        logger.log(Level.INFO, "First name: {0}", playerName);
        logger.log(Level.INFO, "Last name: {0}", playerSurname);

        FacesContext.getCurrentInstance().addMessage(null, new FacesMessage("Terms accepted and player registered!"));
        return "done?faces-redirect=true";
    }
    public String termsRejectedAction() {
        Flash flash = FacesContext.getCurrentInstance().getExternalContext().getFlash();

        flash.setKeepMessages(true);
        pullValuesFromFlashAction(null);

        FacesContext.getCurrentInstance().addMessage(null, new FacesMessage("Terms rejected! Player not registered!"));
        return "index?faces-redirect=true";
    }
}

我认为不需要这两行-

flash.setKeepMessages(true);
pullValuesFromFlashAction(null);

与 terms.xhtml 页面上的 flash.keep 具有相同的目的。作者这里好像有点糊涂了

或者我完全错了&他们在这里确实有用。

Answer 1

作者选择的代码有点混乱，但从我的角度来看，它确实达到了预期的效果。

flash.setKeepMessages(true);

这一行告诉 JSF 您希望将 FacesMessage 保留在 flash 作用域中。这是进行重定向时的一项要求，因为涉及多个后续请求，否则消息会从一个请求到另一个请求而消失。该行是必要的。

pullValuesFromFlashAction(null);

该行没有什么特别之处，只是从 flash 范围中获取名字和姓氏。从 preRenderView 调用它以从 flash 范围加载 bean 数据是正确的，但是从操作方法调用它是 多余的 （除非你想做一些日志记录到查看参数设置是否正确）。无论如何，如果您是从 JSF 开始的，我鼓励您使用 JSF 2.2，它具有 preRenderView 方法的无参数替换，称为 viewAction.

最后但并非最不重要的一点，我建议您阅读 an answer 我前段时间展示了一个处理 flash 示波器的示例，您可能会发现它很有趣。

另请参阅：

JSF Keep Messages docs
How to show faces message in the redirected page

flash.keep & flash.setKeepMessages(true) 重定向

flash.keep & flash.setKeepMessages(true) on redirection

jsf

redirect

jsf-2

messages

flash-scope