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Shalini Sher

Joined: Sep 28, 2004
Posts: 22
For res.sendRedirect(), res.sendError(), and rd.forward, I am seeing inconsistent documentation with regards to if an IllegalStateException will be thrown or not, if the calls have already been made and if we write more to the response.

For instance, the code

public void do Post(req,res)
PrintWriter out = res.getWriter(); // line 1
out.print(" hello "); // line 2
res.sendError(res.SC_NOT_FOUND); // line 3
out.print(); // line 4

Will out.print() at line 4 throw an IllegalStateException?

What is the behavior the same for forward() and sendRedirect().

The servlet api has the following comments for sendError() - but this does not indicate if an exception will be thrown or not..It just mentions that the response should not be written to.

" If the response has already been committed, this method throws an IllegalStateException. After using this method, the response should be considered to be committed and should not be written to. "

I have seen totally inconsistent answers for this question in the different books/practice exams that I have read/taken. Could someone please clarify this.
Jayanthi Mani

Joined: Dec 08, 2000
Posts: 25
My idea will be to just try the example out and see if it throws an IllegalStateException or not.
Mikalai Zaikin
Ranch Hand

Joined: Jun 04, 2002
Posts: 3314
This may not work in real situation, because Writer object probably will have some buffer, and unless this buffer is not flushed, no Exception will be thrown.

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It is sorta covered in the JavaRanch Style Guide.
subject: IllegalStateException
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