Servlet Mapping Recursion Problem
In my web.xml I set up the servlet mapping, for a (front) servlet to handle all requests for the web app, to '/'. This works to the extent that all requests are passed to the servlet. BUT... if I do a forward to another resource from the servlet, the servlet's doGet() method is invoked recursively with no response generated until the jvm runs out of memory. The same thing happens with a url-pattern of '/*'. If the servlet itself generates html output, that works. If I map my servlet to a specific resource, like /index.html, forwarding works fine, but the servlet cant handle all requests and 'http://myhost/myapp' returns 'no directory browsing'. The url-pattern '/' seems like a valid directory specification (as per the servlet 2.2 spec, 'Servlet Mapping Techniques') and a front component, handling all requests is fundamental in the j2EE blueprints (http://java.sun.com/j2ee/blueprints/index.html, section 10.6), so my approach seems architecturally reasonable. I've looked thru the archives and found two reports of the same problem. A proposed workaround from Magnus seems to recommend explicitly mapping every request your app generates (which would make the web.xml coding difficult to maintain in a large app) pendng the delivery of 'filters', perhaps in Servlet 2.3. I dont really understand what Magnus is suggesting: PS: If you're bound to 2.2 or lower then you will not be able to use Filters, in that case you'd have to apply a more complex solution with duplicate resource roots and so on. It looks like 'no front servlets on Orion' to me, but I hope I'm wrong. I was not able to find any references to the problem on bugzilla, but I'm not very adept with its query interface. My hunch is that Orion's request dispatcher is invoked in two contexts (from a client, and from a forward) and does not distinguishbetween them when it comes to selectinga resource to respond to the client. Ifthe dispatcher ignored mapping in the forward context and just accepted the specified resource, the recursion problem would vanish and the front servlet would trap ALL client requests as per the blueprint architecture. Just a hunch, things are probably not that simple. Does anyone know if this is a problem with other webservers ? My experience with Apache was all static pages. My environment is NT4(sp6), Orion 1.4.8, IE 5.00, JDK 1.2.2. Also, if somebody is actually using the front servlet pattern and univeral mapping on Orion, and could let me know how to set it up and/or get around the recursion I'd be a happy camper. TIA, Bill.
RE: Servlet Mapping Recursion Problem
Bill, yeh...we need the apache url re-writting stuff in a servlet. That's an issue with orion. I think the opensymphony people are writing something. There is a simple workaround. Have a forward.jsp as your welcome page for the default app. In the forward.jsp, use this code: % String servletPath = request.getRequestURI().substring(0, request.getRequestURI().indexOf(request.getServletPath())); response.sendRedirect(servletPath+"/somepath/to/index or home or whatever.html") ; % the somepath can be /main/home.html, for example. in your web.xml, map your "controller-rewriter servlet" to the /main/* so instead of yourpages asking for resouces at /myfavoritegif.gif, they would just be /main/myfavoritegif.gif. This is ugly, and quick and dirty, but it works. You can even read in an xml file when you rewriter servlet starts up so that all of your path mapping, rewritting works like apache. Regards, The elephantwalker -Original Message-From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bill WinspurSent: Thursday, May 10, 2001 8:51 AMTo: Orion-InterestSubject: Servlet Mapping Recursion Problem In my web.xml I set up the servlet mapping, for a (front) servlet to handle all requests for the web app, to '/'. This works to the extent that all requests are passed to the servlet. BUT... if I do a forward to another resource from the servlet, the servlet's doGet() method is invoked recursively with no response generated until the jvm runs out of memory. The same thing happens with a url-pattern of '/*'. If the servlet itself generates html output, that works. If I map my servlet to a specific resource, like /index.html, forwarding works fine, but the servlet cant handle all requests and 'http://myhost/myapp' returns 'no directory browsing'. The url-pattern '/' seems like a valid directory specification (as per the servlet 2.2 spec, 'Servlet Mapping Techniques') and a front component, handling all requests is fundamental in the j2EE blueprints (http://java.sun.com/j2ee/blueprints/index.html, section 10.6), so my approach seems architecturally reasonable. I've looked thru the archives and found two reports of the same problem. A proposed workaround from Magnus seems to recommend explicitly mapping every request your app generates (which would make the web.xml coding difficult to maintain in a large app) pendng the delivery of 'filters', perhaps in Servlet 2.3. I dont really understand what Magnus is suggesting: PS: If you're bound to 2.2 or lower then you will not be able to use Filters, in that case you'd have to apply a more complex solution with duplicate resource roots and so on. It looks like 'no front servlets on Orion' to me, but I hope I'm wrong. I was not able to find any references to the problem on bugzilla, but I'm not very adept with its query interface. My hunch is that Orion's request dispatcher is invoked in two contexts (from a client, and from a forward) and does not distinguishbetween them when it comes to selectinga resource to respond to the client. Ifthe dispatcher ignored mapping in the forward context and just accepted the specified resource, the recursion problem would vanish and the front servlet would trap ALL client requests as per the blueprint architecture. Just a hunch, things are probably not that simple. Does anyone know if this is a problem with other webservers ? My experience with Apache was all static pages. My environment is NT4(sp6), Orion 1.4.8, IE 5.00, JDK 1.2.2. Also, if somebody is actually using the front servlet pattern and univeral mapping on Orion, and could let me know how to set it up and/or get around the recursion I'd be a happy camper. TIA, Bill.
Re: Servlet Mapping Recursion Problem
Hi Bill! I am using a front servlet pattern with Orion. I use Struts but I suppose this approach should work in any framework. 1. The front servlet mapping in web.xml: servlet-mapping servlet-nameaction/servlet-name url-pattern*.html/url-pattern /servlet-mapping So all the requests ending to .html are processed by the front-end servlet. 2. All the valid URL's are mapped in an xml config file. The front servlet initializes its state by reading this file in a startup. An entry in this file looks like: actionpath=/faq type=org.shiftctrl.general.interaction.EmptyAction forward name=success path=/faq.jsp/ /action This means that the request http://myserver.com/faq.html is first processed by front servlet. The servlet searches its configured mapping and forwards the request. In this case it would forward the request to faq.jsp. I haven't had problems with this setup and I really like it for following reasons: 1. It is easy pipeline actions. Just configure the mapping so that its forward part points to another mapping. 2. You can hide the technology being used. Clients only see URLs which are always ending .html (so .jsps are not exposed outside, their function is only to provide the view part in MVC pattern) 3. It is possible to dynamically change the URL mapping by calling appropriate methods in front servlet. -- Joni [EMAIL PROTECTED] Bill Winspur wrote: In my web.xml I set up the servlet mapping, for a (front) servlet to handle all requests for the web app, to '/'. This works to the extent that all requests are passed to the servlet. BUT... if I do a forward to another resource from the servlet, the servlet's doGet() method is invoked recursively with no response generated until the jvm runs out of memory. The same thing happens with a url-pattern of '/*'. If the servlet itself generates html output, that works. If I map my servlet to a specific resource, like /index.html, forwarding works fine, but the servlet cant handle all requests and 'http://myhost/myapp' returns 'no directory browsing'. The url-pattern '/' seems like a valid directory specification (as per the servlet 2.2 spec, 'Servlet Mapping Techniques') and a front component, handling all requests is fundamental in the j2EE blueprints (http://java.sun.com/j2ee/blueprints/index.html, section 10.6), so my approach seems architecturally reasonable. I've looked thru the archives and found two reports of the same problem. A proposed workaround from Magnus seems to recommend explicitly mapping every request your app generates (which would make the web.xml coding difficult to maintain in a large app) pendng the delivery of 'filters', perhaps in Servlet 2.3. I dont really understand what Magnus is suggesting: PS: If you're bound to 2.2 or lower then you will not be able to use Filters, in that case you'd have to apply a more complex solution with duplicate resource roots and so on. It looks like 'no front servlets on Orion' to me, but I hope I'm wrong. I was not able to find any references to the problem on bugzilla, but I'm not very adept with its query interface. My hunch is that Orion's request dispatcher is invoked in two contexts (from a client, and from a forward) and does not distinguish between them when it comes to selecting a resource to respond to the client. If the dispatcher ignored mapping in the forward context and just accepted the specified resource, the recursion problem would vanish and the front servlet would trap ALL client requests as per the blueprint architecture. Just a hunch, things are probably not that simple. Does anyone know if this is a problem with other webservers ? My experience with Apache was all static pages. My environment is NT4(sp6), Orion 1.4.8, IE 5.00, JDK 1.2.2. Also, if somebody is actually using the front servlet pattern and univeral mapping on Orion, and could let me know how to set it up and/or get around the recursion I'd be a happy camper. TIA, Bill.
Re: Servlet Mapping Recursion Problem
Thanks Joni, very elegant. I've started down that route (ie. having externally visible urls that are different to the internally visible urls), but hadn't thought of driving the whole thing off a configuration file. Neat. The application provider could package it with the app, leaving the front servlet truly generic. Also, the *.html servlet-mapping hides *.gif resource mapping, etc. from the servlet.. And reason number four to like this approach is: it should work on any webserver. After my previous post I discovered that recursion doesn't just happen if the '/' is mapped to your front servlet (it seems obvious now). If you map 'myUrl' to your front servlet, and then forward to 'myUrl', you also get recursion and a crash. Its been a good day, Bill. - Original Message - From: Joni Suominen [EMAIL PROTECTED] To: Orion-Interest [EMAIL PROTECTED] Sent: Friday, May 11, 2001 11:48 AM Subject: Re: Servlet Mapping Recursion Problem Hi Bill! I am using a front servlet pattern with Orion. I use Struts but I suppose this approach should work in any framework. 1. The front servlet mapping in web.xml: servlet-mapping servlet-nameaction/servlet-name url-pattern*.html/url-pattern /servlet-mapping So all the requests ending to .html are processed by the front-end servlet. 2. All the valid URL's are mapped in an xml config file. The front servlet initializes its state by reading this file in a startup. An entry in this file looks like: actionpath=/faq type=org.shiftctrl.general.interaction.EmptyAction forward name=success path=/faq.jsp/ /action This means that the request http://myserver.com/faq.html is first processed by front servlet. The servlet searches its configured mapping and forwards the request. In this case it would forward the request to faq.jsp. I haven't had problems with this setup and I really like it for following reasons: 1. It is easy pipeline actions. Just configure the mapping so that its forward part points to another mapping. 2. You can hide the technology being used. Clients only see URLs which are always ending .html (so .jsps are not exposed outside, their function is only to provide the view part in MVC pattern) 3. It is possible to dynamically change the URL mapping by calling appropriate methods in front servlet. -- Joni [EMAIL PROTECTED] Bill Winspur wrote: In my web.xml I set up the servlet mapping, for a (front) servlet to handle all requests for the web app, to '/'. This works to the extent that all requests are passed to the servlet. BUT... if I do a forward to another resource from the servlet, the servlet's doGet() method is invoked recursively with no response generated until the jvm runs out of memory. The same thing happens with a url-pattern of '/*'. If the servlet itself generates html output, that works. If I map my servlet to a specific resource, like /index.html, forwarding works fine, but the servlet cant handle all requests and 'http://myhost/myapp' returns 'no directory browsing'. The url-pattern '/' seems like a valid directory specification (as per the servlet 2.2 spec, 'Servlet Mapping Techniques') and a front component, handling all requests is fundamental in the j2EE blueprints (http://java.sun.com/j2ee/blueprints/index.html, section 10.6), so my approach seems architecturally reasonable. I've looked thru the archives and found two reports of the same problem. A proposed workaround from Magnus seems to recommend explicitly mapping every request your app generates (which would make the web.xml coding difficult to maintain in a large app) pendng the delivery of 'filters', perhaps in Servlet 2.3. I dont really understand what Magnus is suggesting: PS: If you're bound to 2.2 or lower then you will not be able to use Filters, in that case you'd have to apply a more complex solution with duplicate resource roots and so on. It looks like 'no front servlets on Orion' to me, but I hope I'm wrong. I was not able to find any references to the problem on bugzilla, but I'm not very adept with its query interface. My hunch is that Orion's request dispatcher is invoked in two contexts (from a client, and from a forward) and does not distinguish between them when it comes to selecting a resource to respond to the client. If the dispatcher ignored mapping in the forward context and just accepted the specified resource, the recursion problem would vanish and the front servlet would trap ALL client requests as per the blueprint architecture. Just a hunch, things are probably not that simple. Does anyone know if this is a problem with other webservers ? My experience with Apache was all static pages. My environment is NT4(sp6), Orion 1.4.8, IE 5.00, JDK 1.2.2. Also, if somebody is actually using the front servlet pattern and univeral mapping on Orion, and could let me know how
