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Question

No long-running conversations - IllegalArgumentException: Stack must not be null

Answer 1

+1 A:

First of all, it is always helpful to see the relevant code and stacktrace when trying to debug a problem.

Thus I cannot give an answer to your first question. However, I will try to explain how the conversation model works.

This is from the Seam in Action book:

@ScopeType.EVENT = Goes from Restore View to Render Response, but not redirect @ScopeType.CONVERSATION = Goes from Restore VIew to Render Response, and redirect. If long-running conversation, then it spans multiple JSF life cycles.

So imagine you are in a.xhtml you push a button that will take ComponentA and fill some data in it. This component you want to inject and use in b.xhtml ie:

Push commandbutton in a.xhtml performing post, putting some data in ComponentA Now you redirect to next page (b.xhtml)which uses the ComponentA

@Name("componentB")
@Scope(ScopeType.CONVERSATION)
public class ComponentB {
    @In(create=true)
    ComponentA componentA; //OK
}

So if you now push another button from b.xhtml expecting to be able to inject ComponentA again, that will fail. ie:

@Name("componentC")
@Scope(ScopeType.CONVERSATION)
public class ComponentC {
    @In(create=true)
    ComponentA componentA; //Injection of the component you really want fails (you will get default component)
}

So in the background now, seam has created a new cid for you, ending the previous cid because a conversation scoped component can only live one request.

Shervin 2010-04-13 13:50:41

@Shervin Interesting, Shervin (+1) Why does Injection of the ComponentA fails when injecting in ComponentC (I suppose it is because of create=true) Am i right ?

Arthur Ronald F D Garcia 2010-04-13 13:58:29

@Shervin None of the pages has a component. I only have two minimal pages with h:commandButtons and the corresponding navigation xml files. Note that I do not begin or end any conversations in the xml files either.

Markos Fragkakis 2010-04-13 14:09:16

@Arthur Ronald F D Garcia: No that is not why it fails. Actually the create=true (if there is no @AutoCreate on the component) makes it `not` fail. When you have create=true, it will create the component if it is not in the scope. The reason why I say fail, is because the component you really want (the injected with the correct fields) is not available, because it has already been garbage collected. You have to promote to long-running conversation if you want to be able to use the component in the "second" redirect.

Shervin 2010-04-13 14:26:51

@Markos Fragkakis How can you use `h:commandButton` without a component? Please show the xhtml files also, not only stacktrace.

Shervin 2010-04-13 14:28:47

If you have no `@AutoCreate` and no `create=true` and only `@In` you will either get a nullpointerexception, or a "RequiredException" stating you need create=true or to give scope explicit.

Shervin 2010-04-13 14:30:34

@Shervin please see update.

Markos Fragkakis 2010-04-13 14:35:20

@Shervin You can avoid create attribute by using a Expression Language (lookup with option to create). Something like @In("#{componentA}"), Seam creates one if it does not exist.

Arthur Ronald F D Garcia 2010-04-13 14:39:37

@Arthur: Yes I know that. EL does auto create, but I wouldn't recommend injecting components through EL. although its quite handy to perform restrict checks in EL: ie `@In("#{s:hasRole('admin')}") boolean isAdmin;`

Shervin 2010-04-13 18:24:13

Answer 2

+1 A:

After seeing your StackTrace and your Use case (after a random number of clicks)

Let's see FacesManages.beforeRedirect (as shown by your StackTrace) documentation

Temporarily promote a temporary conversation to a long running conversation for the duration of a browser redirect

Now, let's see some piece of code of beforeRedirect method

if (isDifferentConversationId(currentPage, targetPage))
    updateCurrentConversationId(targetPage.getConversationId());

...

updateCurrentConversationId is responsible for creating the Stack which must be not null See again your StackTrace

public void updateCurrentConversationId(String id) {
    if (id != null && id.equals(currentConversationId)) {
     // The conversation id has not changed, do nothing       
     return;
  }

After code shown above, your Stack will be created. So i suppose The conversation id has not changed because of The duration of a browser redirect (caused by a random number of clicks) or even a Seam bug when dealing with a navigation with redirect from one page to another and vice-versa

Try the following one for each Page rule (see timeout="0")

<page view-id="/pageA.xhtml" timeout="0">
    <navigation>
        <rule if-outcome="showPageB">
            <redirect view-id="/pageB.xhtml" />
        </rule>
    </navigation>
</page>

I expect now it works fine! But, if not, now, you know why you get your exception

UPDATE

Try <end-conversation/> as a workaround (for each page)

<page view-id="/pageA.xhtml">
    <navigation>
        <rule if-outcome="showPageB">
            <end-conversation/>
            <redirect view-id="/pageB.xhtml" />
        </rule>
    </navigation>
</page>

or (see before-redirect)

<page view-id="/pageA.xhtml">
    <navigation>
        <rule if-outcome="showPageB">
            <end-conversation before-redirect="true"/>
            <redirect view-id="/pageB.xhtml" />
        </rule>
    </navigation>
</page>

Now i hope it works fine!

EDIT

As said by beforeRedirect method

Temporarily promote a temporary conversation to a long running conversation for the duration of a browser redirect. After the redirect, the conversation will be demoted back to a temporary conversation.

1° It explains why #{conversation.longRunning} outputs true when you go to pageB. Your "long running conversation" caused by your redirect should be destroyed after the Render Response phase.

When using a redirect, Seam appends conversation id paratemer to URL.

Seam in Action book says

At the beginning of the Seam life cycle, Seam looks for the conversation id in a URL parameter

But because when you are back to pageA, you see again the same conversation id parameter, I suppose Seam just create a new one when the url does not contain anyone. And because each long running conversation has it own Timeout period, your long running conversation is keeped alive.

To verify whether what i said is true, do as follows

reduce global Timeout period to five seconds (5000 milliseconds)

...

<core:manager conversation-timeout="5000"/>

For each Page, see what #{conversation.timeout} outputs. I expect to see something like Either 5 seconds or 5000 miliseconds. Wait for more than 5 seconds (about 10s) and press button to redirect again. And see whether conversation id parameter has been changed.

Arthur Ronald F D Garcia 2010-04-13 15:27:40

@Arthur thanks for the answer (+1). Unfortunately, I still get the exception. I read in Seam in Action that the page-defined timeout is used to override the one defined in <core:init>, which specifies when *abandoned* conversations end. Even if it did affect my conversation, the redirect-after-post only lasts some milliseconds, which is much less that 1h.

Markos Fragkakis 2010-04-13 15:47:29

@Markos Fragkakis See https://jira.jboss.org/jira/browse/JBSEAM-3901 and http://www.seamframework.org/Community/SeamAddsUnwantedConversationIdToURL

Arthur Ronald F D Garcia 2010-04-13 16:19:52

@Arthur Yes, I saw that yesterday. In that issue they have disabled the redirect filter, whereas I have it by default on.

Markos Fragkakis 2010-04-13 16:24:27

Answer 3

A:

You should have provided that information long ago. Now it is much more clear what the problem is.

First of all you shouldn't use a commandButton with an empty action like that. When you in pages.xml write the following:

<page view-id="/pageA.xhtml">
<navigation>
    <rule if-outcome="showPageB">
        <redirect view-id="/pageB.xhtml" />
    </rule>
</navigation>
</page>

It means normally that you have some action that returns showPageB like this:

public String someAction() {
    //Do something complex
    return "showPageB";
}

Anyhow, back to your problem. Do your self a favor and create a Seam component.

@Name("myComponent")
public Class MyComponent {

public String showPageB() {
    return "showPageB";
}

public String showPageA() {
    return "showPageA";
}

}

Change your pages.xml to this:

<page view-id="/pageA.xhtml">
<navigation from action="#{myComponent.showPageB}">
    <redirect view-id="/pageB.xhtml" />
</navigation>

<navigation from action="#{myComponent.showPageA}">
    <redirect view-id="/pageA.xhtml" />
</navigation>

<!-- OR you can do like this -->
<navigation from action="#{myComponent.showPageB}">
    <rule if-outcome="showPageA">
        <redirect view-id="/pageA.xhtml" />
    </rule>
    <rule if-outcome="showPageB">
        <redirect view-id="/pageA.xhtml" />
    </rule>
</navigation>
</page>

Then change xhtml h:commandButton to

<h:commandButton action="#{myComponent.showPageA}" value="showA"/>
<h:commandButton action="#{myComponent.showPageB}" value="showB"/>

Shervin 2010-04-14 07:57:10

the action attribute *can* be a String: http://www.horstmann.com/corejsf/jsf-tags.html#Table4_15. Why have the overhead of creating a Bean to make a navigation? Let;s say this is my home page. If i press the "Help" button I always want to navigate to the Help page, no bean or method is needed to determine the action.

Markos Fragkakis 2010-04-14 09:30:41

Nevertheless, I did what you suggest, and does not solve my problem... Thanks anyway!

Markos Fragkakis 2010-04-14 10:41:43

I can't believe it doesn't work. That is simply not possible. That means the error is somewhere else in your seam setup.But why would you want to make a post for a simple navigation? What I use is `<s:link viewId="pageA.xhtml" value="Go to A"/>`You should also read the seam documentation found in http://seamframework.org/Documentation

Shervin 2010-04-14 10:58:23

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No long-running conversations - IllegalArgumentException: Stack must not be null

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