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How to use JSP tags as servlet filter?
I have an application based on a single servlet, something of a front controller. I would like to add some jsp tag based post processing. How can I write a filter (post) and send output of my servlet to a jsp engine?
So, my url is http://localhost/MyServlet?action=play. After I have processed the servlet, my response will contain some jsp tags, for example:
<html>
<jsp:expression>new java.util.Date().toString(
</html>
Now I want these tags to be processed by some jsp tag engine invoked from filter and to get final result:
<html>
15.10.2008
</html>
So, my url is http://localhost/MyServlet?action=play. After I have processed the servlet, my response will contain some jsp tags, for example:
<html>
<jsp:expression>new java.util.Date().toString(
</html>
Now I want these tags to be processed by some jsp tag engine invoked from filter and to get final result:
<html>
15.10.2008
</html>
ASKER
The thing is, I don't have a .jsp file. My "your.jsp" is actually servlet output, that's why it contains jsp tag. I don't have static jsp files. My servlet is generating html and now I would like it to hold some jsp tags as well.
So you are essentially building a code generator. But unless you are planning to save the servlet response onto the file system as a JSP file for later use I don't see the value in using JSP technology. The value of JSP is the embedding of dynamic content into static HTML. JSP must be compiled by a servlet container into Java code before it can be used.
Maybe if you posted the exact problem you are trying to solve we could help find you a solution.
Maybe if you posted the exact problem you are trying to solve we could help find you a solution.
I think you will have to create a JSP. It doesn't have to be "static". It can be dynamic. It can respond differently to each set of request parameters sent to it.
ASKER
peter:
We have our own html generator using our inhouse tags.It uses single servlet as front controller. It all works fine and dandy. We now want to add some post-processing that would include jsp tags.
I have posted the exact problem, take a look at the original question:
My servlet will produce jsp source. Now I need to process it with jsp processor before sending it back to the client. And yes, the source it has to be compiled, but I don't see why it can't be done on the fly (Let's say that at the moment I am not worried about performance).
In conclusion, I do not want to generate and save jsp file to the file system and then redirect user to that jsp, I want to output all at once by original servlet.
Please let me know if this is clear, I hope I have managed to explain the problem.
We have our own html generator using our inhouse tags.It uses single servlet as front controller. It all works fine and dandy. We now want to add some post-processing that would include jsp tags.
I have posted the exact problem, take a look at the original question:
My servlet will produce jsp source. Now I need to process it with jsp processor before sending it back to the client. And yes, the source it has to be compiled, but I don't see why it can't be done on the fly (Let's say that at the moment I am not worried about performance).
In conclusion, I do not want to generate and save jsp file to the file system and then redirect user to that jsp, I want to output all at once by original servlet.
Please let me know if this is clear, I hope I have managed to explain the problem.
ASKER
rrz:
I thank you for your support. But do you know HOW I can accomplish that? I know that I can generate jsp page and save it to the disk and then redirect user to the page, but I need to eliminate the intermediate step and send the response with my servlet all in one go.
I thank you for your support. But do you know HOW I can accomplish that? I know that I can generate jsp page and save it to the disk and then redirect user to the page, but I need to eliminate the intermediate step and send the response with my servlet all in one go.
>But do you know HOW I can accomplish that?
Please explain your more clearly. What can't you accomplish ?
The request parameter idea was just a simple example. A better way would be to create a javabean(request or session scoped) to hold your data that is generated from servlet. You can forward to the JSP which has code something like
${yourBean.htmlBlockOne}
${yourBean.dateOne}
${yourBean.htmlBlockTwo}
${yourBean.dateTwo}
${yourBean.htmlBlockThree}
Please explain your more clearly. What can't you accomplish ?
The request parameter idea was just a simple example. A better way would be to create a javabean(request or session scoped) to hold your data that is generated from servlet. You can forward to the JSP which has code something like
${yourBean.htmlBlockOne}
${yourBean.dateOne}
${yourBean.htmlBlockTwo}
${yourBean.dateTwo}
${yourBean.htmlBlockThree}
ASKER CERTIFIED SOLUTION
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ASKER
rrz@:
I want my servlet to return html to browser, not to send the redirect via URL to .jsp.
As I said:
So, my url is http://localhost/MyServlet?action=play. After I have processed the servlet, my response will contain some jsp tags, for example:
<html>
<jsp:expression>new java.util.Date().toString(
</html>
Now I want these tags to be processed by some jsp tag engine invoked from filter and to get final result:
<html>
15.10.2008
</html>
I do not want a servlet to respond with redirect.
I want my servlet to return html to browser, not to send the redirect via URL to .jsp.
As I said:
So, my url is http://localhost/MyServlet?action=play. After I have processed the servlet, my response will contain some jsp tags, for example:
<html>
<jsp:expression>new java.util.Date().toString(
</html>
Now I want these tags to be processed by some jsp tag engine invoked from filter and to get final result:
<html>
15.10.2008
</html>
I do not want a servlet to respond with redirect.
>invoked from filter
What do you mean ? Are you talking about an object that implements the javax.servlet.Filter interface ?
>Now I want these tags to be processed by some jsp tag engine
As far as I know, a request must be made to engage the JSP engine.
What do you mean ? Are you talking about an object that implements the javax.servlet.Filter interface ?
>Now I want these tags to be processed by some jsp tag engine
As far as I know, a request must be made to engage the JSP engine.
ASKER
>What do you mean ? Are you talking about an object that implements the javax.servlet.Filter interface ?
Yes, of course. As I said, I have my own servlet doing front controller and I do not want to change this. I want to put jsp processing into the picture and filter seems the most logical way to do it.
>As far as I know, a request must be made to engage the JSP engine.
Not really. JSP engines are just java libraries. I would like to invoke JSP engine programatically.
Something like
org.apache.jasper.servlet.
servlet.service(request, response);
That's where I need some help...
Yes, of course. As I said, I have my own servlet doing front controller and I do not want to change this. I want to put jsp processing into the picture and filter seems the most logical way to do it.
>As far as I know, a request must be made to engage the JSP engine.
Not really. JSP engines are just java libraries. I would like to invoke JSP engine programatically.
Something like
org.apache.jasper.servlet.
servlet.service(request, response);
That's where I need some help...
>I would like to invoke JSP engine programatically.
I don't know how to do that.
I have a crazy idea. Make a JSP file for each tag that you want to use. These JSP files will only contain one tag each and get a request parameter to use as its body. Name them mytag1.jsp , mytag2.jsp , and so on. In your Filter's doFilter method parse the response from your servlet and find each tag. Use a java.net.HttpURLConnection
Personally I think you should redesign and use JSP in the standard way.
I don't know how to do that.
I have a crazy idea. Make a JSP file for each tag that you want to use. These JSP files will only contain one tag each and get a request parameter to use as its body. Name them mytag1.jsp , mytag2.jsp , and so on. In your Filter's doFilter method parse the response from your servlet and find each tag. Use a java.net.HttpURLConnection
Personally I think you should redesign and use JSP in the standard way.
ASKER
rrz:
Could you provide small example for your crazy idea?
What do you mean by "and get a request parameter to use as its body?
If I understand correctly, this means that if I have let's say 30 tags in my page, I'll need to invoke 30 jsp pages? That doesn't sound that great...
Could you provide small example for your crazy idea?
What do you mean by "and get a request parameter to use as its body?
If I understand correctly, this means that if I have let's say 30 tags in my page, I'll need to invoke 30 jsp pages? That doesn't sound that great...
> if I have let's say 30 tags in my page, I'll need to invoke 30 jsp pages?
If they all different tags, then yes.
>That doesn't sound that great...
No, it doesn't.
>and get a request parameter to use as its body
For example, mytag1.jsp would contain
<my:tag1>${param.body}</my
and you would call it with
URL url = new URL("mytag1.jsp ?body=" + java.net.URLEncoder.encode
HttpURLConnection urlConnection = (HttpURLConnection)(url.op
If they all different tags, then yes.
>That doesn't sound that great...
No, it doesn't.
>and get a request parameter to use as its body
For example, mytag1.jsp would contain
<my:tag1>${param.body}</my
and you would call it with
URL url = new URL("mytag1.jsp ?body=" + java.net.URLEncoder.encode
HttpURLConnection urlConnection = (HttpURLConnection)(url.op
SOLUTION
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RequestDispatcher rd = getServletContext().getReq
rd.forward(request,respons
and in your.jsp you could use
${param.d}