Re: [JBoss-user] MDB...why?
Hello Peter: Let's go with another example and you would say me if (now, at last, thanks god ;-) am i in the correct way: An imaginary assumption: i wanna write an application to manage a Mail List in this way: Topic publisher side -- A servlet obtains a lot of information (news) about 'Sport', 'Cinema' and 'Computers'. This program sends messages to a Topic which include 'subject', 'theme' and 'body' fields. Topic subscriber side - Three (diferent) listeners called 'listenSport', 'listenCinema' and 'listenComputers' wait for a message with its 'theme' field equals to 'Sport', 'Cinema' or 'Computers', respectively. Each Listener will call outers Session Beans which transform the 'body' field in an HTML format (for Sports), PDF format (for Cinema) and Plain-text format (for Computers) and then, every Session Bean send an e-mail to [EMAIL PROTECTED], [EMAIL PROTECTED] or [EMAIL PROTECTED] with its respective attachment. Everything will occur without 'bothering' the servlet. In the other hand, writing 3 diferent Listeners will allow us to change (separately) the formating task asociated to each Listener, and, in the future, add new Listeners for new themes. Regards: __ Jaume Soriano Sivera [EMAIL PROTECTED] __ [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 15/05/2001 21:43 Please respond to jboss-user To: [EMAIL PROTECTED] cc: Subject:Re: [JBoss-user] MDB...why? On 14 Maj, [EMAIL PROTECTED] wrote: Thank you Per!! The origin of this confusion is a sample in JBoss Documentation, making more specific: example called MDB as a Listener. How many subscribers appear in this example? I think a subscriber is 'Worker Bean', isn't it? Then, to have more than one subscriber i've to create other Beans similar (or not) to Worker Bean, haven't i? So, if i create new beans i have to modify my Listener to be able to comunicate with the new subscriber... The ListenerBean is the subscriber. The logic is partitioned so that the work is done in the stateless session bean. Not that it is necesarry in this example, but only to show how it is possible to do it. When it commes to an MDB, you deploy one version (name, configuration) for each logic and topic/selector combination. Some areas to use this? - A time task run in JMX could send its task to a queue. An MDB listens for missions and delegate to a sessiion bean (or does the work for itself). - A bean get some cind of thing to do. To continue it need to wait one some cind of event (perhaps the presence of something). It triggers this and returns. A message bean listens on a queue where the event will be placed and calls the session bean (that perhaps has saves som temporary persistens data throug an entity bean from the earlier invokation, which it now uses. //Peter Please, am i in the correct way? Thank you again! __ Jaume Soriano Sivera [EMAIL PROTECTED] __ Per Lewau [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 14/05/2001 13:08 Please respond to jboss-user To: [EMAIL PROTECTED] cc: Subject:Re: [JBoss-user] MDB...why? On Mon, 14 May 2001 [EMAIL PROTECTED] wrote: Hi: I'm testing JBoss with MDB but i'm still lost about its utility... I'd like to write an application to manage a little web-shop using EJBs and MDBs as follows: * A java servlet who takes data from web application, i.e. the identifier of a client who wants to buy a book. * Before allowing this purchase i want to check if this client is not in my 'defaulter list'. * After this i'll be able to avoid/allow the purchase. Well, i though to do this: The servlet takes data from web client and sends it to a Topic, then Topic sends data to a Checker Bean that runs a method called 'checkClient' wich look for this client in a 'defaulter' database. If everything is ok, a 'true' value is returned to servlet Sounds more like a Queue than a Topic to me. Queues are for point-to-point messages and Topics are for Publisher/Subscriber (many receivers). Is this a good way to pose my problem? I know its possible to develope *the same* without MDBs, but, is there any advantage on using MDBs? in other words, how can i take advantage of MDBs? I'm not sure what you are trying to do, but this is my take on what you want. 0. MDB listens for messages on in queue 1. serlvet sends message to in queue with whatever should be checked 2. servlet waits for message on out queue 3. MDB.onMessage() called 4. MDB checks whatever 5. MDB sends message (true or false) to out queue 6. servlet receives message and proceeds I'd say that the advantage of MDBs is that they can be called asynchronously. What you want
Re: [JBoss-user] MDB...why?
On 16 Maj, [EMAIL PROTECTED] wrote: Hello Peter: Let's go with another example and you would say me if (now, at last, thanks god ;-) am i in the correct way: Hi, sound like a perfect match, and a good example to. Remember, if the sessions beans all have the same remote interface, the code for the MDB may be exactly the same. You could specify the name of the session bean in the deployment descriptor, which means that adding a new listener is just a matter of configuring the deploymentdescriptors and deploy into the running server. //Peter An imaginary assumption: i wanna write an application to manage a Mail List in this way: Topic publisher side -- A servlet obtains a lot of information (news) about 'Sport', 'Cinema' and 'Computers'. This program sends messages to a Topic which include 'subject', 'theme' and 'body' fields. Topic subscriber side - Three (diferent) listeners called 'listenSport', 'listenCinema' and 'listenComputers' wait for a message with its 'theme' field equals to 'Sport', 'Cinema' or 'Computers', respectively. Each Listener will call outers Session Beans which transform the 'body' field in an HTML format (for Sports), PDF format (for Cinema) and Plain-text format (for Computers) and then, every Session Bean send an e-mail to [EMAIL PROTECTED], [EMAIL PROTECTED] or [EMAIL PROTECTED] with its respective attachment. Everything will occur without 'bothering' the servlet. In the other hand, writing 3 diferent Listeners will allow us to change (separately) the formating task asociated to each Listener, and, in the future, add new Listeners for new themes. Regards: __ Jaume Soriano Sivera [EMAIL PROTECTED] __ [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 15/05/2001 21:43 Please respond to jboss-user To: [EMAIL PROTECTED] cc: Subject:Re: [JBoss-user] MDB...why? On 14 Maj, [EMAIL PROTECTED] wrote: Thank you Per!! The origin of this confusion is a sample in JBoss Documentation, making more specific: example called MDB as a Listener. How many subscribers appear in this example? I think a subscriber is 'Worker Bean', isn't it? Then, to have more than one subscriber i've to create other Beans similar (or not) to Worker Bean, haven't i? So, if i create new beans i have to modify my Listener to be able to comunicate with the new subscriber... The ListenerBean is the subscriber. The logic is partitioned so that the work is done in the stateless session bean. Not that it is necesarry in this example, but only to show how it is possible to do it. When it commes to an MDB, you deploy one version (name, configuration) for each logic and topic/selector combination. Some areas to use this? - A time task run in JMX could send its task to a queue. An MDB listens for missions and delegate to a sessiion bean (or does the work for itself). - A bean get some cind of thing to do. To continue it need to wait one some cind of event (perhaps the presence of something). It triggers this and returns. A message bean listens on a queue where the event will be placed and calls the session bean (that perhaps has saves som temporary persistens data throug an entity bean from the earlier invokation, which it now uses. //Peter Please, am i in the correct way? Thank you again! __ Jaume Soriano Sivera [EMAIL PROTECTED] __ Per Lewau [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 14/05/2001 13:08 Please respond to jboss-user To: [EMAIL PROTECTED] cc: Subject:Re: [JBoss-user] MDB...why? On Mon, 14 May 2001 [EMAIL PROTECTED] wrote: Hi: I'm testing JBoss with MDB but i'm still lost about its utility... I'd like to write an application to manage a little web-shop using EJBs and MDBs as follows: * A java servlet who takes data from web application, i.e. the identifier of a client who wants to buy a book. * Before allowing this purchase i want to check if this client is not in my 'defaulter list'. * After this i'll be able to avoid/allow the purchase. Well, i though to do this: The servlet takes data from web client and sends it to a Topic, then Topic sends data to a Checker Bean that runs a method called 'checkClient' wich look for this client in a 'defaulter' database. If everything is ok, a 'true' value is returned to servlet Sounds more like a Queue than a Topic to me. Queues are for point-to-point messages and Topics are for Publisher/Subscriber (many receivers). Is this a good way to pose my problem? I know its possible to develope *the same* without MDBs, but, is there any advantage on using MDBs? in other words, how can i take
Re: [JBoss-user] MDB...why?
On 14 Maj, [EMAIL PROTECTED] wrote: Thank you Per!! The origin of this confusion is a sample in JBoss Documentation, making more specific: example called MDB as a Listener. How many subscribers appear in this example? I think a subscriber is 'Worker Bean', isn't it? Then, to have more than one subscriber i've to create other Beans similar (or not) to Worker Bean, haven't i? So, if i create new beans i have to modify my Listener to be able to comunicate with the new subscriber... The ListenerBean is the subscriber. The logic is partitioned so that the work is done in the stateless session bean. Not that it is necesarry in this example, but only to show how it is possible to do it. When it commes to an MDB, you deploy one version (name, configuration) for each logic and topic/selector combination. Some areas to use this? - A time task run in JMX could send its task to a queue. An MDB listens for missions and delegate to a sessiion bean (or does the work for itself). - A bean get some cind of thing to do. To continue it need to wait one some cind of event (perhaps the presence of something). It triggers this and returns. A message bean listens on a queue where the event will be placed and calls the session bean (that perhaps has saves som temporary persistens data throug an entity bean from the earlier invokation, which it now uses. //Peter Please, am i in the correct way? Thank you again! __ Jaume Soriano Sivera [EMAIL PROTECTED] Tel: 96504 -ext. 44744 Fax: 965040047 Portal y servicios multimedia - Nuevas tecnologias W a n a d o o E s p a n a - http://www.wanadoo.es __ Per Lewau [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 14/05/2001 13:08 Please respond to jboss-user To: [EMAIL PROTECTED] cc: Subject:Re: [JBoss-user] MDB...why? On Mon, 14 May 2001 [EMAIL PROTECTED] wrote: Hi: I'm testing JBoss with MDB but i'm still lost about its utility... I'd like to write an application to manage a little web-shop using EJBs and MDBs as follows: * A java servlet who takes data from web application, i.e. the identifier of a client who wants to buy a book. * Before allowing this purchase i want to check if this client is not in my 'defaulter list'. * After this i'll be able to avoid/allow the purchase. Well, i though to do this: The servlet takes data from web client and sends it to a Topic, then Topic sends data to a Checker Bean that runs a method called 'checkClient' wich look for this client in a 'defaulter' database. If everything is ok, a 'true' value is returned to servlet Sounds more like a Queue than a Topic to me. Queues are for point-to-point messages and Topics are for Publisher/Subscriber (many receivers). Is this a good way to pose my problem? I know its possible to develope *the same* without MDBs, but, is there any advantage on using MDBs? in other words, how can i take advantage of MDBs? I'm not sure what you are trying to do, but this is my take on what you want. 0. MDB listens for messages on in queue 1. serlvet sends message to in queue with whatever should be checked 2. servlet waits for message on out queue 3. MDB.onMessage() called 4. MDB checks whatever 5. MDB sends message (true or false) to out queue 6. servlet receives message and proceeds I'd say that the advantage of MDBs is that they can be called asynchronously. What you want to do sound synchronous and while possible to do it just adds a lot of overhead. A session bean is easier and faster. To me it seems as though MDBs are useful for triggering some action that you don't want to hang around waiting for. For instance, you might want to send an email with an order confirmation and personally I wouldn't want to hang around in my process order session bean waiting for JavaMail to finish (after all it is talking SMTP to a mail server somewhere) so I would simple put a message in a queue and let an MDB deal with the sending of emails. Regards, Per --- Per Lewau ([EMAIL PROTECTED]) Why waste time learning, when ignorance is instantaneous? - Hobbes ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user -- Peter Antman Technology in Media, Box 34105 100 26 Stockholm Systems ArchitectWWW: http://www.tim.se Email: [EMAIL PROTECTED]WWW: http://www.backsource.org Phone: +46-(0)8-506 381 11 Mobile: 070-675 3942
[JBoss-user] MDB...why?
Hi: I'm testing JBoss with MDB but i'm still lost about its utility... I'd like to write an application to manage a little web-shop using EJBs and MDBs as follows: * A java servlet who takes data from web application, i.e. the identifier of a client who wants to buy a book. * Before allowing this purchase i want to check if this client is not in my 'defaulter list'. * After this i'll be able to avoid/allow the purchase. Well, i though to do this: The servlet takes data from web client and sends it to a Topic, then Topic sends data to a Checker Bean that runs a method called 'checkClient' wich look for this client in a 'defaulter' database. If everything is ok, a 'true' value is returned to servlet Is this a good way to pose my problem? I know its possible to develope *the same* without MDBs, but, is there any advantage on using MDBs? in other words, how can i take advantage of MDBs? Excuse me if these questions sounds so 'simple' but i need a little help to understand MDB cause i'm really interested in learning everything about JBOSS. Thanks in advance! __ Jaume Soriano Sivera [EMAIL PROTECTED] __ ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user
Re: [JBoss-user] MDB...why?
Thank you Per!! The origin of this confusion is a sample in JBoss Documentation, making more specific: example called MDB as a Listener. How many subscribers appear in this example? I think a subscriber is 'Worker Bean', isn't it? Then, to have more than one subscriber i've to create other Beans similar (or not) to Worker Bean, haven't i? So, if i create new beans i have to modify my Listener to be able to comunicate with the new subscriber... Please, am i in the correct way? Thank you again! __ Jaume Soriano Sivera [EMAIL PROTECTED] Tel: 96504 -ext. 44744 Fax: 965040047 Portal y servicios multimedia - Nuevas tecnologias W a n a d o o E s p a n a - http://www.wanadoo.es __ Per Lewau [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 14/05/2001 13:08 Please respond to jboss-user To: [EMAIL PROTECTED] cc: Subject:Re: [JBoss-user] MDB...why? On Mon, 14 May 2001 [EMAIL PROTECTED] wrote: Hi: I'm testing JBoss with MDB but i'm still lost about its utility... I'd like to write an application to manage a little web-shop using EJBs and MDBs as follows: * A java servlet who takes data from web application, i.e. the identifier of a client who wants to buy a book. * Before allowing this purchase i want to check if this client is not in my 'defaulter list'. * After this i'll be able to avoid/allow the purchase. Well, i though to do this: The servlet takes data from web client and sends it to a Topic, then Topic sends data to a Checker Bean that runs a method called 'checkClient' wich look for this client in a 'defaulter' database. If everything is ok, a 'true' value is returned to servlet Sounds more like a Queue than a Topic to me. Queues are for point-to-point messages and Topics are for Publisher/Subscriber (many receivers). Is this a good way to pose my problem? I know its possible to develope *the same* without MDBs, but, is there any advantage on using MDBs? in other words, how can i take advantage of MDBs? I'm not sure what you are trying to do, but this is my take on what you want. 0. MDB listens for messages on in queue 1. serlvet sends message to in queue with whatever should be checked 2. servlet waits for message on out queue 3. MDB.onMessage() called 4. MDB checks whatever 5. MDB sends message (true or false) to out queue 6. servlet receives message and proceeds I'd say that the advantage of MDBs is that they can be called asynchronously. What you want to do sound synchronous and while possible to do it just adds a lot of overhead. A session bean is easier and faster. To me it seems as though MDBs are useful for triggering some action that you don't want to hang around waiting for. For instance, you might want to send an email with an order confirmation and personally I wouldn't want to hang around in my process order session bean waiting for JavaMail to finish (after all it is talking SMTP to a mail server somewhere) so I would simple put a message in a queue and let an MDB deal with the sending of emails. Regards, Per --- Per Lewau ([EMAIL PROTECTED]) Why waste time learning, when ignorance is instantaneous? - Hobbes ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user
Re: [JBoss-user] MDB...why?
Hi, as far as I understand, MDB's are designed for 2 main issues. 1. to enable an asynchrone communication mechanism (i.e. to trigger some actions where the client has no need to wait for the result.) 2. to enable a listener mechanism where sending and recieving processes could be connected in a very flexible way (i.e. a new listener is connected to en existing Topic to do additional things, so you must not change anything in the former part of your app.) In your case, the sending process has to know the result of the operation, so I think this is no good design to use MDBs in this part. A good place for an MDB may be the part where you trigger the next steps in handling the purchase ( i.e. tell the workers to pack the books and write a bill). HTH tom On Mon, 14 May 2001, you wrote: Hi: I'm testing JBoss with MDB but i'm still lost about its utility... I'd like to write an application to manage a little web-shop using EJBs and MDBs as follows: * A java servlet who takes data from web application, i.e. the identifier of a client who wants to buy a book. * Before allowing this purchase i want to check if this client is not in my 'defaulter list'. * After this i'll be able to avoid/allow the purchase. Well, i though to do this: The servlet takes data from web client and sends it to a Topic, then Topic sends data to a Checker Bean that runs a method called 'checkClient' wich look for this client in a 'defaulter' database. If everything is ok, a 'true' value is returned to servlet Is this a good way to pose my problem? I know its possible to develope *the same* without MDBs, but, is there any advantage on using MDBs? in other words, how can i take advantage of MDBs? Excuse me if these questions sounds so 'simple' but i need a little help to understand MDB cause i'm really interested in learning everything about JBOSS. Thanks in advance! __ Jaume Soriano Sivera [EMAIL PROTECTED] __ ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user -- THETA - Consulting Kommuniktionsanalyse - Anwendungsentwicklung - LINUX-Systeme Thomas Hagedorn Tel. 07231-472108 Rainstr. 12 Tel. 0172-7642398 75217 Birkenfeld [EMAIL PROTECTED] Jesus inside - where do you want to go forever ? ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user
New: [JBoss-user] MDB...why?
(Excuse me if this e-mail appears twice) Thank you Per!! The origin of this confusion is a sample in JBoss Documentation, making more specific: example called MDB as a Listener. How many subscribers appear in this example? I think a subscriber is 'Worker Bean', isn't it? Then, to have more than one subscriber i've to create other Beans similar (or not) to Worker Bean, haven't i? So, if i create new beans i have to modify my Listener to be able to comunicate with the new subscriber... Please, am i in the correct way? Thank you again! __ Jaume Soriano Sivera [EMAIL PROTECTED] Tel: 96504 -ext. 44744 Fax: 965040047 Portal y servicios multimedia - Nuevas tecnologias W a n a d o o E s p a n a - http://www.wanadoo.es __ Per Lewau [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 14/05/2001 13:08 Please respond to jboss-user To: [EMAIL PROTECTED] cc: Subject:Re: [JBoss-user] MDB...why? On Mon, 14 May 2001 [EMAIL PROTECTED] wrote: Hi: I'm testing JBoss with MDB but i'm still lost about its utility... I'd like to write an application to manage a little web-shop using EJBs and MDBs as follows: * A java servlet who takes data from web application, i.e. the identifier of a client who wants to buy a book. * Before allowing this purchase i want to check if this client is not in my 'defaulter list'. * After this i'll be able to avoid/allow the purchase. Well, i though to do this: The servlet takes data from web client and sends it to a Topic, then Topic sends data to a Checker Bean that runs a method called 'checkClient' wich look for this client in a 'defaulter' database. If everything is ok, a 'true' value is returned to servlet Sounds more like a Queue than a Topic to me. Queues are for point-to-point messages and Topics are for Publisher/Subscriber (many receivers). Is this a good way to pose my problem? I know its possible to develope *the same* without MDBs, but, is there any advantage on using MDBs? in other words, how can i take advantage of MDBs? I'm not sure what you are trying to do, but this is my take on what you want. 0. MDB listens for messages on in queue 1. serlvet sends message to in queue with whatever should be checked 2. servlet waits for message on out queue 3. MDB.onMessage() called 4. MDB checks whatever 5. MDB sends message (true or false) to out queue 6. servlet receives message and proceeds I'd say that the advantage of MDBs is that they can be called asynchronously. What you want to do sound synchronous and while possible to do it just adds a lot of overhead. A session bean is easier and faster. To me it seems as though MDBs are useful for triggering some action that you don't want to hang around waiting for. For instance, you might want to send an email with an order confirmation and personally I wouldn't want to hang around in my process order session bean waiting for JavaMail to finish (after all it is talking SMTP to a mail server somewhere) so I would simple put a message in a queue and let an MDB deal with the sending of emails. Regards, Per --- Per Lewau ([EMAIL PROTECTED]) Why waste time learning, when ignorance is instantaneous? - Hobbes ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user
Re: New: [JBoss-user] MDB...why?
I seemed to have ranted abit, but I hope you'll find this useful. On Mon, 14 May 2001 [EMAIL PROTECTED] wrote: (Excuse me if this e-mail appears twice) Thank you Per!! The origin of this confusion is a sample in JBoss Documentation, making more specific: example called MDB as a Listener. How many subscribers appear in this example? One. The ListernerBean is the one subscriber to the Topic topic/testTopic. I think a subscriber is 'Worker Bean', isn't it? The subscriber is the ListernerBean. When the listener bean receives a message it calls the WorkerBean. Then, to have more than one subscriber i've to create other Beans similar (or not) to Worker Bean, haven't i? (I see know why you talked about using a Topic in your last mail (that's what's great about helping others, innit?). The reason for using a topic is to be able to send an event to many event listeners.) The Worker bean is an ordinary Session Bean and is not directly involved in the JMS thingy. Lets call a message published on the topic a WorkEvent that triggers that work should be done (man, I'd hate one of those ;). In the example the ListenerBean receives that event and instead of doing the work himself he delegates (sweet) it to the WorkerBean. If you'd want more beans to listen to that event then yes, you'd have to modify the ListenerBean to also call those other beans. The idea is that there should be one Topic for all events and that the ListenerBean is responisble for sending events on to other beans (the actual listeners, so to speak). I'd say that the idea is a little lost in the example as it is too simple. The advantage of having one Topic and one subscriber is that you only have to reconfigure that subscriber, something which could be done via the environment. The advantage doesn't really become apparent when you have only one event; you could just attach many MDBs to that Topic. However, when you want to add more events you'd have to add more Topics and that would require restarting the server (right now, Topics added while the server is running are not recreated when the server is restarted (are they?)). So, if i create new beans i have to modify my Listener to be able to comunicate with the new subscriber... Yes. Please, am i in the correct way? You are. Cheers On Mon, 14 May 2001 [EMAIL PROTECTED] wrote: Hi: I'm testing JBoss with MDB but i'm still lost about its utility... I'd like to write an application to manage a little web-shop using EJBs and MDBs as follows: * A java servlet who takes data from web application, i.e. the identifier of a client who wants to buy a book. * Before allowing this purchase i want to check if this client is not in my 'defaulter list'. * After this i'll be able to avoid/allow the purchase. Well, i though to do this: The servlet takes data from web client and sends it to a Topic, then Topic sends data to a Checker Bean that runs a method called 'checkClient' wich look for this client in a 'defaulter' database. If everything is ok, a 'true' value is returned to servlet Sounds more like a Queue than a Topic to me. Queues are for point-to-point messages and Topics are for Publisher/Subscriber (many receivers). Is this a good way to pose my problem? I know its possible to develope *the same* without MDBs, but, is there any advantage on using MDBs? in other words, how can i take advantage of MDBs? I'm not sure what you are trying to do, but this is my take on what you want. 0. MDB listens for messages on in queue 1. serlvet sends message to in queue with whatever should be checked 2. servlet waits for message on out queue 3. MDB.onMessage() called 4. MDB checks whatever 5. MDB sends message (true or false) to out queue 6. servlet receives message and proceeds I'd say that the advantage of MDBs is that they can be called asynchronously. What you want to do sound synchronous and while possible to do it just adds a lot of overhead. A session bean is easier and faster. To me it seems as though MDBs are useful for triggering some action that you don't want to hang around waiting for. For instance, you might want to send an email with an order confirmation and personally I wouldn't want to hang around in my process order session bean waiting for JavaMail to finish (after all it is talking SMTP to a mail server somewhere) so I would simple put a message in a queue and let an MDB deal with the sending of emails. Regards, Per --- Per Lewau ([EMAIL PROTECTED]) Why waste time learning, when ignorance is instantaneous? - Hobbes ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user ___ JBoss-user mailing list [EMAIL PROTECTED]
RE: [JBoss-user] MDB...why?
Hi I really don't know if you need a MDB. You can achieve your goal by the servlet invoking the Checker bean directly. You're functinality is synchronous in nature. YOu could use MDB to do the same, however it would be unnecessary use of resources. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Per Lewau Sent: Monday, May 14, 2001 7:08 AM To: [EMAIL PROTECTED] Subject: Re: [JBoss-user] MDB...why? On Mon, 14 May 2001 [EMAIL PROTECTED] wrote: Hi: I'm testing JBoss with MDB but i'm still lost about its utility... I'd like to write an application to manage a little web-shop using EJBs and MDBs as follows: * A java servlet who takes data from web application, i.e. the identifier of a client who wants to buy a book. * Before allowing this purchase i want to check if this client is not in my 'defaulter list'. * After this i'll be able to avoid/allow the purchase. Well, i though to do this: The servlet takes data from web client and sends it to a Topic, then Topic sends data to a Checker Bean that runs a method called 'checkClient' wich look for this client in a 'defaulter' database. If everything is ok, a 'true' value is returned to servlet Sounds more like a Queue than a Topic to me. Queues are for point-to-point messages and Topics are for Publisher/Subscriber (many receivers). Is this a good way to pose my problem? I know its possible to develope *the same* without MDBs, but, is there any advantage on using MDBs? in other words, how can i take advantage of MDBs? I'm not sure what you are trying to do, but this is my take on what you want. 0. MDB listens for messages on in queue 1. serlvet sends message to in queue with whatever should be checked 2. servlet waits for message on out queue 3. MDB.onMessage() called 4. MDB checks whatever 5. MDB sends message (true or false) to out queue 6. servlet receives message and proceeds I'd say that the advantage of MDBs is that they can be called asynchronously. What you want to do sound synchronous and while possible to do it just adds a lot of overhead. A session bean is easier and faster. To me it seems as though MDBs are useful for triggering some action that you don't want to hang around waiting for. For instance, you might want to send an email with an order confirmation and personally I wouldn't want to hang around in my process order session bean waiting for JavaMail to finish (after all it is talking SMTP to a mail server somewhere) so I would simple put a message in a queue and let an MDB deal with the sending of emails. Regards, Per --- Per Lewau ([EMAIL PROTECTED]) Why waste time learning, when ignorance is instantaneous? - Hobbes ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user ___ JBoss-user mailing list [EMAIL PROTECTED] http://lists.sourceforge.net/lists/listinfo/jboss-user
