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From "Frank W. Zammetti" <fzli...@omnytex.com>
Subject Re: is there a possibility to define the startup order for webapps?
Date Mon, 24 Apr 2006 17:33:04 GMT
One could envision a rather complex and somewhat funky solution to 
this... I'm not so sure I'd recommend it, but in the interest of 
creative thinking...

(1) Add a context parameter isAppRunning to the webapp, initially set to 
"false".

(2) Create a filter that is mapped to handle all requests.  It checks 
the value of isAppRunning, and redirects to some page if the value is 
"false".

(3) Create a ContextListener that fires off a daemon thread.

(4) The daemon thread makes a simple request to some predefined URL of 
the other webapp.  If it does not get the response it expects, it sleeps 
for a second or two and then tries again.

(5) When the daemon thread gets the reply it expects, it sets 
isAppRunning to "true" and dies.

Now, add this all to the "master" webapp, that is, the one that depends 
on the other.  All requests should be blocked and redirected to the page 
of your choice until the webapp it depends on returns that OK reply.  I 
could envision this being done with a number of webapps, forming a 
dependency chain not unlike "depends" in Ant.

Will it work?  I think so, but I just made it up, so who knows :)

Frank

SOA Work wrote:
> argh. annoying.
> ok. thx anyway.
> 
>> -----Urspr√ľngliche Nachricht-----
>> Von: "Tomcat Users List" <users@tomcat.apache.org>
>> Gesendet: 24.04.06 17:57:49
>> An: "Tomcat Users List" <users@tomcat.apache.org>
>> Betreff: Re: is there a possibility to define the startup order for webapps?
> 
> 
>> A couple of other ideas:
>>
>> Use a small shared class (in shared/lib) to keep track of whether the
>> database is running. The first webapp notifies this class when it's
>> ready, and the second webapp checks if the database is ready before
>> using it.
>>
>> Or, just accept that database errors will occur during startup. This
>> is not a bad solution. From a user's point of view, when the server is
>> down all requests will return some kind of error, until the server is
>> back up and running. The only thing you can hope to gain is a better
>> error message for a few seconds during startup.
>> --
>> Len
>>
>>
>> On 4/24/06, David Smith <dns4@cornell.edu> wrote:
>>> This question comes up every so often and the answer is always no. The
>>> webapp load order cannot be relied upon. In your case, might I suggest
>>> the database webapp be run on a separate instance of tomcat?  Can the
>>> connection be done via TCP/IP?
>>>
>>>  --David
>>>
>>> SOA Work wrote:
>>>> Hi there,
>>>>
>>>> I'm currenttly using tomcat 5.x for running my webapps. Now I have the following
problem:
>>>>
>>>> I'm using an database system which runs as webapplication inside tomcat.
>>>> Another webapplication needs the database connection for startup.
>>>> Everytime I restart tomcat the server doesn't get up, because the second
webapp ist started before the database webapp.
>>>>
>>>> Is there a way to define the startup order of the webapplications deployed
on a server?
>>>> With wich system does tomcat choose the apps while startup? Could it be a
possibility to rename the folder of the webapps?
>>>>
>>>> thx
>>>> Dominik
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>>>
>>> --
>>> David Smith
>>> Network Operations Supervisor
>>> Department of Entomology
>>> Cornell University
>>> 2132 Comstock Hall
>>> Ithaca, NY 14853
>>> Phone: (607) 255-9571
>>> Fax: (607) 255-0940
>>>
>>>
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> 
> 
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> 
> 

-- 
Frank W. Zammetti
Founder and Chief Software Architect
Omnytex Technologies
http://www.omnytex.com
AIM: fzammetti
Yahoo: fzammetti
MSN: fzammetti@hotmail.com
Java Web Parts -
http://javawebparts.sourceforge.net
Supplying the wheel, so you don't have to reinvent it!

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