Re: Asynchronous messages from servlets
Ronald Wildenberg wrote: What I need is a way to push the response to the browser. I would like the server to take the initiative in updating the browser window, not the user. Is this possible in any way? No way. HTTP is a pull-mechanism: information is always requested by the client. Solutions: push a mail to the user or let the generated HTML page repeatedly update itself. The latter is an HTTP/HTML feature that is not part of the W3C standards but works quite well with most standard browsers, nevertheless. Add meta http-equiv=refresh content=5; URL=http://selfhtml.teamone.de/; to your HTML page header, and the browser will replace the page after five seconds by the one specified in the URL. Regards, Hans -- To unsubscribe: mailto:[EMAIL PROTECTED] For additional commands: mailto:[EMAIL PROTECTED] Troubles with the list: mailto:[EMAIL PROTECTED]
Re: Asynchronous messages from servlets
On Tuesday 22 January 2002 8:50 am, you wrote: Hi, I have the following problem. A simple form submits data to a servlet. The servlet sends a message via JMS to another application (in another JVM). Once the message has been sent, the 'service' method of the servlet ends. After a while, say five seconds, the other application would like to send back a response. How do I show this response to the user? Since the 'service' method has finished after sending the message, I have lost control over the output from the other application. What I need is a way to push the response to the browser. I would like the server to take the initiative in updating the browser window, not the user. Is this possible in any way? Thanks in advance, Ronald Wildenberg You could do the following. If the client has JVM and permissions can be arranged to listen on a specific port (and any firewalls are going to allow the traffic etc) then: When sending your small form include a java applet that creates a task that simply listens on a specific port. Your asynchronous process can then return a message to that port. This has been done. (with IBM MQSeries java API) Good Luck regards, David. -- To unsubscribe: mailto:[EMAIL PROTECTED] For additional commands: mailto:[EMAIL PROTECTED] Troubles with the list: mailto:[EMAIL PROTECTED]
Re: Asynchronous messages from servlets
On Tue, 22 Jan 2002, Ronald Wildenberg wrote: Date: Tue, 22 Jan 2002 09:50:14 +0100 From: Ronald Wildenberg [EMAIL PROTECTED] Reply-To: Tomcat Users List [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Asynchronous messages from servlets Hi, I have the following problem. A simple form submits data to a servlet. The servlet sends a message via JMS to another application (in another JVM). Once the message has been sent, the 'service' method of the servlet ends. After a while, say five seconds, the other application would like to send back a response. How do I show this response to the user? Since the 'service' method has finished after sending the message, I have lost control over the output from the other application. What I need is a way to push the response to the browser. I would like the server to take the initiative in updating the browser window, not the user. Is this possible in any way? Thanks in advance, Ronald Wildenberg There are two pieces to the answer for this kind of thing -- getting the data back from the other JVM (I assume you are using asynchronous JMS calls, right?), and displaying the data back to the user. For the first step, doing an asynchronous JMS call in the other direction (to a JMS receiver in the same JVM as Tomcat) could then receive the results, and make them available as a servlet context or session attribute. For the second, I've seen people set up a page that uses the meta-refresh capability in HTML to automatically keep sending a request every XX seconds. The servlet that receives this request will check to see if the results are back yet - if they are, they are displayed, if they are not it shows a Request in Progress ... please wait page with the meta refresh tag. The key thing is that you won't be able to respond on the original HTTP request, since that has already been sent and your service() method has returned. Craig -- To unsubscribe: mailto:[EMAIL PROTECTED] For additional commands: mailto:[EMAIL PROTECTED] Troubles with the list: mailto:[EMAIL PROTECTED]
Re: Asynchronous messages from servlets
- Original Message - From: Craig R. McClanahan [EMAIL PROTECTED] To: Tomcat Users List [EMAIL PROTECTED] Sent: Tuesday, January 22, 2002 1:04 PM Subject: Re: Asynchronous messages from servlets On Tue, 22 Jan 2002, Ronald Wildenberg wrote: Date: Tue, 22 Jan 2002 09:50:14 +0100 From: Ronald Wildenberg [EMAIL PROTECTED] Reply-To: Tomcat Users List [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Asynchronous messages from servlets Hi, I have the following problem. A simple form submits data to a servlet. The servlet sends a message via JMS to another application (in another JVM). Once the message has been sent, the 'service' method of the servlet ends. After a while, say five seconds, the other application would like to send back a response. How do I show this response to the user? Since the 'service' method has finished after sending the message, I have lost control over the output from the other application. What I need is a way to push the response to the browser. I would like the server to take the initiative in updating the browser window, not the user. Is this possible in any way? Thanks in advance, Ronald Wildenberg There are two pieces to the answer for this kind of thing -- getting the data back from the other JVM (I assume you are using asynchronous JMS calls, right?), and displaying the data back to the user. For the first step, doing an asynchronous JMS call in the other direction (to a JMS receiver in the same JVM as Tomcat) could then receive the results, and make them available as a servlet context or session attribute. For the second, I've seen people set up a page that uses the meta-refresh capability in HTML to automatically keep sending a request every XX seconds. The servlet that receives this request will check to see if the results are back yet - if they are, they are displayed, if they are not it shows a Request in Progress ... please wait page with the meta refresh tag. The key thing is that you won't be able to respond on the original HTTP request, since that has already been sent and your service() method has returned. Craig [...] Thanks for your info! if the processing of asynchronous JMS calls will be responsed in short time by JMS-Thread, is the following(half-synchronous way) also possible? - use javax.servlet.ServletResponse.flushBuffer() to show a info(please wait...) to client - make a asynchronous JMS calls - block this Servlet-Thread, wait for a event sent by JMS - when the event comes, the blocking ends, then the results are responsed to client, and the Servlet-Thread ends. I am not sure about: - can javax.servlet.ServletResponse.flushBuffer() always response info to client before the Servlet-Thread ends(so the client can get please wait... info)? in my testing, it works, but some emails say that sometimes it can not work. - is this half-synchronous way a good Servlet-DesignPattern if I can be sure that the blocking will not need a long-time? or it is not good? Thanks in advance! Bo Jan222002 -- To unsubscribe: mailto:[EMAIL PROTECTED] For additional commands: mailto:[EMAIL PROTECTED] Troubles with the list: mailto:[EMAIL PROTECTED]
Re: Asynchronous messages from servlets
On Tue, 22 Jan 2002, Bo Xu wrote: Date: Tue, 22 Jan 2002 13:41:10 -0500 From: Bo Xu [EMAIL PROTECTED] Reply-To: Tomcat Users List [EMAIL PROTECTED] To: Tomcat Users List [EMAIL PROTECTED] Subject: Re: Asynchronous messages from servlets - Original Message - From: Craig R. McClanahan [EMAIL PROTECTED] To: Tomcat Users List [EMAIL PROTECTED] Sent: Tuesday, January 22, 2002 1:04 PM Subject: Re: Asynchronous messages from servlets On Tue, 22 Jan 2002, Ronald Wildenberg wrote: Date: Tue, 22 Jan 2002 09:50:14 +0100 From: Ronald Wildenberg [EMAIL PROTECTED] Reply-To: Tomcat Users List [EMAIL PROTECTED] To: [EMAIL PROTECTED] Subject: Asynchronous messages from servlets Hi, I have the following problem. A simple form submits data to a servlet. The servlet sends a message via JMS to another application (in another JVM). Once the message has been sent, the 'service' method of the servlet ends. After a while, say five seconds, the other application would like to send back a response. How do I show this response to the user? Since the 'service' method has finished after sending the message, I have lost control over the output from the other application. What I need is a way to push the response to the browser. I would like the server to take the initiative in updating the browser window, not the user. Is this possible in any way? Thanks in advance, Ronald Wildenberg There are two pieces to the answer for this kind of thing -- getting the data back from the other JVM (I assume you are using asynchronous JMS calls, right?), and displaying the data back to the user. For the first step, doing an asynchronous JMS call in the other direction (to a JMS receiver in the same JVM as Tomcat) could then receive the results, and make them available as a servlet context or session attribute. For the second, I've seen people set up a page that uses the meta-refresh capability in HTML to automatically keep sending a request every XX seconds. The servlet that receives this request will check to see if the results are back yet - if they are, they are displayed, if they are not it shows a Request in Progress ... please wait page with the meta refresh tag. The key thing is that you won't be able to respond on the original HTTP request, since that has already been sent and your service() method has returned. Craig [...] Thanks for your info! if the processing of asynchronous JMS calls will be responsed in short time by JMS-Thread, is the following(half-synchronous way) also possible? - use javax.servlet.ServletResponse.flushBuffer() to show a info(please wait...) to client - make a asynchronous JMS calls - block this Servlet-Thread, wait for a event sent by JMS - when the event comes, the blocking ends, then the results are responsed to client, and the Servlet-Thread ends. I am not sure about: - can javax.servlet.ServletResponse.flushBuffer() always response info to client before the Servlet-Thread ends(so the client can get please wait... info)? in my testing, it works, but some emails say that sometimes it can not work. - is this half-synchronous way a good Servlet-DesignPattern if I can be sure that the blocking will not need a long-time? or it is not good? Thanks in advance! Bo Jan222002 Whether the please wait message will be visible or not is client dependent. I would still model this kind of thing as a separate request with the meta refresh, as I outlined above (you'll need to do the JMS query in a separate thread for this to work). Craig -- To unsubscribe: mailto:[EMAIL PROTECTED] For additional commands: mailto:[EMAIL PROTECTED] Troubles with the list: mailto:[EMAIL PROTECTED]
