RE: [Semi OT] When does a servlet get a session?
That does not compute Your servlet HttpSession is associated with a set of requests that a specific user makes to a particular servlet. You will, at any point have many sessions for 1 instance of your servlet. I believe a session will be created when you call getSession() if one does not already exist (it's specified in the spec and I'm too lazy to look it up). -Original Message- From: Chappell, Simon P [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 12:40 PM To: Struts Mailing List (E-mail) Subject: [Semi OT] When does a servlet get a session? OK, I have a servlet running alongside my Struts application and it is basically used to start (from the init() method) a separate network listener for handling network requests from a number of PLC units that are incapable of generating HTTP traffic, only straight socket connections, blasting a wierd protocol called DF1 and then waiting for a reply. We have all of that working. But now we want to store a piece of information in the servlet session so that we can load-balance on a WAS cluster. When we call back into the servlet to store the information, our session information is null. My question is ... when does a servlet get a session and can we force one from the init method? This servlet never gets called, so we never have an HttpSession. Can we force it to create an HttpSession? Simon - Simon P. Chappell [EMAIL PROTECTED] Java Programming Specialist www.landsend.com Lands' End, Inc. (608) 935-4526 Never give in - never, never, never, never, in nothing great or small, large or petty, never give in except to convictions of honor and good sense. - Sir Winston Churchill - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - This message and its contents (to include attachments) are the property of Kmart Corporation (Kmart) and may contain confidential and proprietary information. You are hereby notified that any disclosure, copying, or distribution of this message, or the taking of any action based on information contained herein is strictly prohibited. Unauthorized use of information contained herein may subject you to civil and criminal prosecution and penalties. If you are not the intended recipient, you should delete this message immediately. - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: [Semi OT] When does a servlet get a session?
If your servlet never services http requests, how is an http session useful? You can only access the session through a request - which you'll never have. Would the servlet context work? getServletContext().setAttribute(...) -- Voytek Jarnot Quantum materiae materietur marmota monax si marmota monax materiam possit materiari? -Original Message- From: Chappell, Simon P [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 11:40 AM To: Struts Mailing List (E-mail) Subject: [Semi OT] When does a servlet get a session? OK, I have a servlet running alongside my Struts application and it is basically used to start (from the init() method) a separate network listener for handling network requests from a number of PLC units that are incapable of generating HTTP traffic, only straight socket connections, blasting a wierd protocol called DF1 and then waiting for a reply. We have all of that working. But now we want to store a piece of information in the servlet session so that we can load-balance on a WAS cluster. When we call back into the servlet to store the information, our session information is null. My question is ... when does a servlet get a session and can we force one from the init method? This servlet never gets called, so we never have an HttpSession. Can we force it to create an HttpSession? Simon - Simon P. Chappell [EMAIL PROTECTED] Java Programming Specialist www.landsend.com Lands' End, Inc. (608) 935-4526 Never give in - never, never, never, never, in nothing great or small, large or petty, never give in except to convictions of honor and good sense. - Sir Winston Churchill - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: [Semi OT] When does a servlet get a session?
You're right that we'll never have an HTTP request, so I can see why you're confused as to why we'd want a session. The reason is for performance. We want to avoid the overhead of writing and reading a database. This is very short term information, but now that we're needing to run in a load-balanced cluster, we need to be able to handle the situation where requests could, in the worst case scenario, come into each server alternatively. IBM's WebSphere App. Server when running in a cluster will propogate the session to any server that needs it. Thus if we use a session, it'll propogate back and forth between the boxes. Simon -Original Message- From: Jarnot Voytek Contr AU HQ/SC [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 11:47 AM To: 'Struts Users Mailing List' Subject: RE: [Semi OT] When does a servlet get a session? If your servlet never services http requests, how is an http session useful? You can only access the session through a request - which you'll never have. Would the servlet context work? getServletContext().setAttribute(...) -- Voytek Jarnot Quantum materiae materietur marmota monax si marmota monax materiam possit materiari? -Original Message- From: Chappell, Simon P [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 11:40 AM To: Struts Mailing List (E-mail) Subject: [Semi OT] When does a servlet get a session? OK, I have a servlet running alongside my Struts application and it is basically used to start (from the init() method) a separate network listener for handling network requests from a number of PLC units that are incapable of generating HTTP traffic, only straight socket connections, blasting a wierd protocol called DF1 and then waiting for a reply. We have all of that working. But now we want to store a piece of information in the servlet session so that we can load-balance on a WAS cluster. When we call back into the servlet to store the information, our session information is null. My question is ... when does a servlet get a session and can we force one from the init method? This servlet never gets called, so we never have an HttpSession. Can we force it to create an HttpSession? Simon - Simon P. Chappell [EMAIL PROTECTED] Java Programming Specialist www.landsend.com Lands' End, Inc. (608) 935-4526 Never give in - never, never, never, never, in nothing great or small, large or petty, never give in except to convictions of honor and good sense. - Sir Winston Churchill - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: [Semi OT] When does a servlet get a session?
Chappell, Simon P wrote: You're right that we'll never have an HTTP request, so I can see why you're confused as to why we'd want a session. The reason is for performance. We want to avoid the overhead of writing and reading a database. This is very short term information, but now that we're needing to run in a load-balanced cluster, we need to be able to handle the situation where requests could, in the worst case scenario, come into each server alternatively. IBM's WebSphere App. Server when running in a cluster will propogate the session to any server that needs it. Thus if we use a session, it'll propogate back and forth between the boxes. The problem you're going to have is that there is no such thing as an HttpSession without an HTTP request. Even if you could do what you propose, it would only make the stored information available to a single user -- that doesn't seem like it will do what you want. A possible strategy to avoid READING the database on every request is to have a webapp startup method load the data into a servlet context attribute. This will happen on each node the app is deployed to, but will happen only once (before the first request is processed). Simon Craig - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: [Semi OT] When does a servlet get a session?
Craig, -Original Message- From: Craig R. McClanahan [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 4:19 PM To: Struts Users Mailing List Subject: Re: [Semi OT] When does a servlet get a session? Chappell, Simon P wrote: You're right that we'll never have an HTTP request, so I can see why you're confused as to why we'd want a session. The reason is for performance. We want to avoid the overhead of writing and reading a database. This is very short term information, but now that we're needing to run in a load-balanced cluster, we need to be able to handle the situation where requests could, in the worst case scenario, come into each server alternatively. IBM's WebSphere App. Server when running in a cluster will propogate the session to any server that needs it. Thus if we use a session, it'll propogate back and forth between the boxes. The problem you're going to have is that there is no such thing as an HttpSession without an HTTP request. We found that out! :-( Even if you could do what you propose, it would only make the stored information available to a single user -- that doesn't seem like it will do what you want. Actually, it is exactly what we want. This servlet only exists to start our socket listener. This is a certifiably awful hack, but they wouldn't let us run a separate server application, so when all you have is a servlet engine, everything looks like a hammer (or something like that). A possible strategy to avoid READING the database on every request is to have a webapp startup method load the data into a servlet context attribute. This will happen on each node the app is deployed to, but will happen only once (before the first request is processed). Actually, we have something like that now, where we store information in a static variable in the servlet. That works fine. The issue is that for WAS to replicate it between server instances, it needs to be in the servlet session that we don't have. The other challenge is that we don't have any control over the DF1 protocol or the serial to IP device that calls our listener. We asked our engineers if they could try faking some HTTP and then we could send the traffic through our existing Struts based system, but it would seem that is not possible with the current hardware situation that they work with. Simon - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: [Semi OT] When does a servlet get a session?
I suppose you could fake the http requests yourself, couldn't you? When the DF1 request comes in, translate it to an http get or post request and send it off to your existing struts system. Translate the http response into whatever is needed for the DF1 response. Also, does this DF1 protocol have any notion of a session? In other words, is there some unique identifier sent with each request to tie it to other requests, or are all requests basically global? Either way, you would need to send an appropriate jsessionid value back with your fake http requests in order to maintain the same http session. Joe - Original Message - From: Chappell, Simon P [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, October 16, 2003 5:31 PM Subject: RE: [Semi OT] When does a servlet get a session? Craig, -Original Message- From: Craig R. McClanahan [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 4:19 PM To: Struts Users Mailing List Subject: Re: [Semi OT] When does a servlet get a session? Chappell, Simon P wrote: You're right that we'll never have an HTTP request, so I can see why you're confused as to why we'd want a session. The reason is for performance. We want to avoid the overhead of writing and reading a database. This is very short term information, but now that we're needing to run in a load-balanced cluster, we need to be able to handle the situation where requests could, in the worst case scenario, come into each server alternatively. IBM's WebSphere App. Server when running in a cluster will propogate the session to any server that needs it. Thus if we use a session, it'll propogate back and forth between the boxes. The problem you're going to have is that there is no such thing as an HttpSession without an HTTP request. We found that out! :-( Even if you could do what you propose, it would only make the stored information available to a single user -- that doesn't seem like it will do what you want. Actually, it is exactly what we want. This servlet only exists to start our socket listener. This is a certifiably awful hack, but they wouldn't let us run a separate server application, so when all you have is a servlet engine, everything looks like a hammer (or something like that). A possible strategy to avoid READING the database on every request is to have a webapp startup method load the data into a servlet context attribute. This will happen on each node the app is deployed to, but will happen only once (before the first request is processed). Actually, we have something like that now, where we store information in a static variable in the servlet. That works fine. The issue is that for WAS to replicate it between server instances, it needs to be in the servlet session that we don't have. The other challenge is that we don't have any control over the DF1 protocol or the serial to IP device that calls our listener. We asked our engineers if they could try faking some HTTP and then we could send the traffic through our existing Struts based system, but it would seem that is not possible with the current hardware situation that they work with. Simon - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: [Semi OT] When does a servlet get a session?
Funny you should suggest that. We're currently considering this as an option. The DF1 protocol is a stone-age protocol used by Allen-Bradley Programmable Logic Controllers and as such is very inflexible. While we work on this, we're gonna work with our load balancer and try to get our sessions to be extra-sticky so that the likelyhood of two different requests from a PLC going to different WAS servers is greatly reduced. It certainly is a pickle of a situation! Simon -Original Message- From: Joseph Fifield [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 6:06 PM To: Struts Users Mailing List Subject: Re: [Semi OT] When does a servlet get a session? I suppose you could fake the http requests yourself, couldn't you? When the DF1 request comes in, translate it to an http get or post request and send it off to your existing struts system. Translate the http response into whatever is needed for the DF1 response. Also, does this DF1 protocol have any notion of a session? In other words, is there some unique identifier sent with each request to tie it to other requests, or are all requests basically global? Either way, you would need to send an appropriate jsessionid value back with your fake http requests in order to maintain the same http session. Joe - Original Message - From: Chappell, Simon P [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, October 16, 2003 5:31 PM Subject: RE: [Semi OT] When does a servlet get a session? Craig, -Original Message- From: Craig R. McClanahan [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 4:19 PM To: Struts Users Mailing List Subject: Re: [Semi OT] When does a servlet get a session? Chappell, Simon P wrote: You're right that we'll never have an HTTP request, so I can see why you're confused as to why we'd want a session. The reason is for performance. We want to avoid the overhead of writing and reading a database. This is very short term information, but now that we're needing to run in a load-balanced cluster, we need to be able to handle the situation where requests could, in the worst case scenario, come into each server alternatively. IBM's WebSphere App. Server when running in a cluster will propogate the session to any server that needs it. Thus if we use a session, it'll propogate back and forth between the boxes. The problem you're going to have is that there is no such thing as an HttpSession without an HTTP request. We found that out! :-( Even if you could do what you propose, it would only make the stored information available to a single user -- that doesn't seem like it will do what you want. Actually, it is exactly what we want. This servlet only exists to start our socket listener. This is a certifiably awful hack, but they wouldn't let us run a separate server application, so when all you have is a servlet engine, everything looks like a hammer (or something like that). A possible strategy to avoid READING the database on every request is to have a webapp startup method load the data into a servlet context attribute. This will happen on each node the app is deployed to, but will happen only once (before the first request is processed). Actually, we have something like that now, where we store information in a static variable in the servlet. That works fine. The issue is that for WAS to replicate it between server instances, it needs to be in the servlet session that we don't have. The other challenge is that we don't have any control over the DF1 protocol or the serial to IP device that calls our listener. We asked our engineers if they could try faking some HTTP and then we could send the traffic through our existing Struts based system, but it would seem that is not possible with the current hardware situation that they work with. Simon - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: [Semi OT] When does a servlet get a session?
You may want to look @ Jigsaw which is HTTP server that can be configured as a HTTP Client (by implementing it as a Proxy). I did this like 5-6 years ago and it served my purpose very well. The HTTP Client would generate the HTTP requests to the web server(s). The response would get cached to disk and processed/transformed to the business logic layer via a client side filter mechanism that Jigsaw has. Should save you from writing a lot of code.. A classic case for the Adapter pattern. Jigsaw is at: http://www.w3.org/Jigsaw/ Mahesh -- Mahesh Joshi W- 408-543-7214 M- 408-829-8051 [EMAIL PROTECTED] -Original Message- From: Chappell, Simon P [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 4:56 PM To: Struts Users Mailing List Subject: RE: [Semi OT] When does a servlet get a session? Funny you should suggest that. We're currently considering this as an option. The DF1 protocol is a stone-age protocol used by Allen-Bradley Programmable Logic Controllers and as such is very inflexible. While we work on this, we're gonna work with our load balancer and try to get our sessions to be extra-sticky so that the likelyhood of two different requests from a PLC going to different WAS servers is greatly reduced. It certainly is a pickle of a situation! Simon -Original Message- From: Joseph Fifield [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 6:06 PM To: Struts Users Mailing List Subject: Re: [Semi OT] When does a servlet get a session? I suppose you could fake the http requests yourself, couldn't you? When the DF1 request comes in, translate it to an http get or post request and send it off to your existing struts system. Translate the http response into whatever is needed for the DF1 response. Also, does this DF1 protocol have any notion of a session? In other words, is there some unique identifier sent with each request to tie it to other requests, or are all requests basically global? Either way, you would need to send an appropriate jsessionid value back with your fake http requests in order to maintain the same http session. Joe - Original Message - From: Chappell, Simon P [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, October 16, 2003 5:31 PM Subject: RE: [Semi OT] When does a servlet get a session? Craig, -Original Message- From: Craig R. McClanahan [mailto:[EMAIL PROTECTED] Sent: Thursday, October 16, 2003 4:19 PM To: Struts Users Mailing List Subject: Re: [Semi OT] When does a servlet get a session? Chappell, Simon P wrote: You're right that we'll never have an HTTP request, so I can see why you're confused as to why we'd want a session. The reason is for performance. We want to avoid the overhead of writing and reading a database. This is very short term information, but now that we're needing to run in a load-balanced cluster, we need to be able to handle the situation where requests could, in the worst case scenario, come into each server alternatively. IBM's WebSphere App. Server when running in a cluster will propogate the session to any server that needs it. Thus if we use a session, it'll propogate back and forth between the boxes. The problem you're going to have is that there is no such thing as an HttpSession without an HTTP request. We found that out! :-( Even if you could do what you propose, it would only make the stored information available to a single user -- that doesn't seem like it will do what you want. Actually, it is exactly what we want. This servlet only exists to start our socket listener. This is a certifiably awful hack, but they wouldn't let us run a separate server application, so when all you have is a servlet engine, everything looks like a hammer (or something like that). A possible strategy to avoid READING the database on every request is to have a webapp startup method load the data into a servlet context attribute. This will happen on each node the app is deployed to, but will happen only once (before the first request is processed). Actually, we have something like that now, where we store information in a static variable in the servlet. That works fine. The issue is that for WAS to replicate it between server instances, it needs to be in the servlet session that we don't have. The other challenge is that we don't have any control over the DF1 protocol or the serial to IP device that calls our listener. We asked our engineers if they could try faking some HTTP and then we could send the traffic through our existing Struts based system, but it would seem that is not possible with the current hardware situation that they work with. Simon - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED
