Removing JSF messages from the flash

问题

I have one page that does something and when the user clicks a button, the user is redirected to another page and a message is displayed. Here is my code:

 public String confirm() {
    FacesContext context = FacesContext.getCurrentInstance();
    Flash flash = context.getExternalContext().getFlash();
    flash.setKeepMessages(true);
    FacesMessage msg = new FacesMessage("Succesful", "Release is confirmed!");
    context.addMessage(null, msg);
    return "/prot/expert/releases?faces-redirect=true";
 }

I use a p:growl component which displays my message on the "releases" page. So far so good.

But then on any subsequent page that has p:growl (or if I go to another page and go back) the message is displayed again and again and I can't kill it.

I tried something like:

<c:set target="#{flash}" property="keepMessages" value="false" />

on the page that has the p:growl, I tried clearing the flash from the backing bean etc.

The message is retained and displayed all over again. If I remove flash.setKeepMessages(true); from the code above then nothing is displayed.

What am I doing wrong?

回答1:

I did get the exact same problem on JBoss AS 6 with both Mojarra 2.0.3 and Mojarra 2.1.1. The flash should survive only one redirect, but in practice it not always does.

In an action method I have basically the same code:

// [add global faces message]
FacesContext.getCurrentInstance().getExternalContext().getFlash().setKeepMessages(true);
return "/someView.xhtml?faces-redirect=true";

I've been seeing three symptoms of the problem:

1. After doing a postback on someView, the flash faces message keeps being displayed
2. After a clean request to a completely different page, the face message is also displayed
3. After going again through the code that adds the faces message, you'll get two of the same messages on someView

Issue 2 can be explained by realizing that the flash scope is cookie based (at least in Mojarra). Relatively few people seem to understand the inherent problem with that. I've found this related question, but it has no answers: Is Flash scope free of race conditions?

Also, when trying to reproduce the problem I've got approximately a 2/3 chance of actually reproducing it. Sometimes it indeed only survives a single redirect, sometimes it's gone after a few refreshes (time based or so?) and sometimes it just sticks around and the only way to get rid of it is restarting my server(!).

Maybe I'm doing something wrong somewhere?

Observing the cookies being set, I noticed the followed:

After initially triggering the action that does the redirect:

POST Response
Set-Cookie csfcfc=_50Xfr

GET Response
Set-Cookie csfcfc=50Xfn_51Xfn

The thing to notice here is that the response from the GET request for the redirect again sets a cookie. You want think that for a flash scope the cookie would need to be deleted here.

If I submit a form on the view towards I'm redirected, the following happens:

POST Response
Set-Cookie csfcfc=_50Xfn

The message is now gone.

However, when I submit the form once more, the following happens:

POST Response
Set-Cookie  csfcfc=_52Xfn

And, the message is back :(

If I again submit the form:

POST Response

There is no more Set-Cookie header and the message in once again gone. If I continue submitting the form, the last cookie (csfcfc=_52Xfn) keeps being send to the server, but there are no more new cookies being set and no messages are displayed.

Edit:

During debugging I came across a critical section in ELFlash.java (Mojarra 2.0.3):

void saveAllMessages(FacesContext context) {
    // take no action on the GET that comes after a REDIRECT
    Map<Object, Object> contextMap = context.getAttributes();
    PreviousNextFlashInfoManager flashManager;
    if (null == (flashManager = getCurrentFlashManager(contextMap, true))) {
        return;
    }
    if (flashManager.getPreviousRequestFlashInfo().isIsRedirect()) {
        return;
    }
}

During the context of the GET request following the redirect, one would suppose isIsRedirect would return true, but it returned false. This could be a local problem, that I'm going to investigate further.

Interesting to note is perhaps that the cookie values actually have some meaning, according to the following:

 FirstTimeThru("f"),
 SecondTimeThru("s"),
 IsRedirect("r"),
 IsNormal("n");

So the first cookie (_50Xfr), is a FirstTimeThru and a IsRedirect.

回答2:

Your concrete problem is caused by a bug in older Mojarra versions, specifically issue 1751. There have however been many issue reports for the flash scope afterwards. The flash scope is in older Mojarra versions known for the following major problems:

• issue 1751 - Flash scoped messages lives longer than next request - fixed in 2.0.7 / 2.1.4
• issue 2126 - Flash cookie enables data exploits - fixed in 2.1.24 / 2.2.1
• issue 2136 - Flash cookie not available when redirected to different path - fixed in 2.1.14 / 2.2.0
• issue 2902 - Flash cookie uses wrong path for applications on root - fixed in 2.1.24 / 2.2.1
• issue 2955 - Flash creates sometimes version1 cookies which fails in IE<=10 - fixed in 2.1.25 / 2.2.2
• issue 2973 - Flash causes NPE on stale cookies after a session expire - fixed in 2.1.25 / 2.2.2
• issue 2862 - Flash cookie not cleared when stale - fixed in 2.1.27 / 2.2.5

All in all, concluded can be that you'd need to upgrade to a minimum of Mojarra 2.1.27 / 2.2.5 (due date 2 january 2014) in order to get rid of all those problems.

回答3:

Try setting property redisplay to false:

<p:growl redisplay="false"/>

来源：https://stackoverflow.com/questions/3343147/removing-jsf-messages-from-the-flash