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Long session - what if commit in the servlet-filter fails?

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pgruber

Post subject: Long session - what if commit in the servlet-filter fails?

Posted: Tue Dec 20, 2005 8:46 am

Newbie

Joined: Tue Jan 18, 2005 7:08 am
Posts: 10

I'm using the "hibernate long session" pattern as described in the book by G.King and C.Bauer (chapter 8). But the problem is: if there happens an error when I try to commit in the servlet-filter (e.g. a constraint problem), I do not know how to let the user know about the problem (with a useful error message).
I'm also using flush(), but this does not solve the problem.

Is there a solution for this problem?

Thanks!

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tchize

Post subject:

Posted: Tue Dec 20, 2005 9:13 am

Senior

Joined: Tue May 10, 2005 9:00 am
Posts: 125

Yes, there is a solution.

You need to wrap the response object to your own class so as to provide the filter chain with a virtual output stream. Then at commit time you can decide either to pass this as is to client or to replace it with your error message.

An example of such filtering can be found at http://www-128.ibm.com/developerworks/java/library/j-tomcat/?open&l=101,t=grj,p=TomcatTricks
See ReplaceTextFilter

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pgruber

Post subject:

Posted: Tue Dec 20, 2005 1:40 pm

Newbie

Joined: Tue Jan 18, 2005 7:08 am
Posts: 10

Ok, I see.

But what if I'm using Struts and would like to call another action (or some other URL)?
Is this possible?

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tchize

Post subject:

Posted: Tue Dec 20, 2005 5:52 pm

Senior

Joined: Tue May 10, 2005 9:00 am
Posts: 125

Then the best thing is to do exactly as you would do to call another servlet inside a servlet.

Use request.getRequestDispatcher("/some/path.do").forward(request, response);

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pgruber

Post subject:

Posted: Wed Dec 21, 2005 4:37 am

Newbie

Joined: Tue Jan 18, 2005 7:08 am
Posts: 10

I already tried this way, but then I get an IllegalStateException because I already accessed the ServletOutputStream.
But whether an error happened or not I only know after that I commit to the DB (and at that time the servlet has already bagun to write to the OutputStream).

1) user wants to commit changes to the DB
2) my filter executes chain
3) the filter tries to commit

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tchize

Post subject:

Posted: Wed Dec 21, 2005 4:47 am

Senior

Joined: Tue May 10, 2005 9:00 am
Posts: 125

That's the reason you must provide your own ServeltOutputStream to the filter chain. Anything the filter chain does on the outputstream will only be send to the client if your filter was able to commit:

Code:

- User do a query
- Filter stores the ServletOutputStream to a local variable
- Filter Create a memory based ServletOutputStream
- Filter call filterchain providing the memory based ServletOutputStream
- filerchain do various thing that end in various outputs
- Filter tries to commit
   - if commit success, Filter copy the memory based ServletOutputStream to the locally saved ServletOutputStream
   - if commit fail, send a redirect using the locally saved ServletOutputStream, don't care about what's in the memory based ServletOutputStream
- Returns

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