Hi All,
I know that finally block executes it self by all means irrespective of any error in the try block. However will it execute even if there is a <jsp:forward page=""/> directive in try block?
e.g:
try
{
Statement1
Statement2
%><jsp:forward page="index.jsp"/><%
Statement3
Statement4
}
finally{
Statement5
Statement6
}
Cheers...
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here is what my textbook says
"The code block in a finally clause is always executed, unless the thread executing the try dies. The purpose of a finally clause is to give the programmer a guaranteed way to dispose of system resources and otherwise clean up before exiting a method. The finally clause is executed regerdless of how the try block is exited."
jspBegin,
The servlet resulting from translating your jsp page would look something like:
try{
Statement1
Statement2
if (true) {
out.clear();
String _jspx_qfStr = "";
_jspx_qfStr = _jspx_qfStr
pageContext.forward("index
return;
}
Statement3
Statement4
}
finally{
Statement5
Statement6
}
// let say you had some more code after the try finally too......
Statement7
Statement8
So in answer to your question:
- Statement3 & 4 will not be executed because of the return statement placed before them.
- Statement5 & 6 will get executed right after execution leaves you try block whether it left because of an exception or because of a explicit return statement Remeber when return is executed, execution leaves the try block then leaves the function, right after leaving the try block it executes the finally block and leaves the function meaning: statement7 & 8 are not executed.
Try executing this example class:
public class BlockTest
{
public static void main(String[] args)
{
try
{
System.out.println( "Inside try - Before return;" );
if( true ) return;
System.out.println( "Inside try - After return;" );
}
finally
{
System.out.println( "Inside finally" );
}
System.out.println( "After finally" );
}
}
Be aware that statement5 & 6 should not attempt to write to the response output because it is going to be committed in the index.jsp page. Doing so will result in an IllegalStateException being thrown.
hope that helps
from the JSP 1.2 spec
"A <jsp:forward page=”urlSpec” /> element allows the runtime dispatch of the
current request to a static resource, a JSP page or a Java servlet class in the same
context as the current page. A jsp:forward effectively terminates the execution of the
current page.
.....If the page output is buffered, the buffer is cleared prior to forwarding.
If the page output is buffered and the buffer was flushed, an attempt to
forward the request will result in an IllegalStateException.
If the page output was unbuffered and anything has been written to it, an
attempt to forward the request will result in an IllegalStateException."
Hi abuimad,
I had some vague idea that finally block provide developers with an option to release resources and thus execute all the time (If you enter try block) but I wasn't very sure. Thanks to you guys that helped me understand this.
I have few more queries though. It would be brilliant if you could help me understand few more basic things:
1. Is it possible that we can access application or session scope variables in a class? I mean If I am using application variables using application.setAttribute/a
2. Also If I edit a class file and change some text (say if the text in a class file is "50" and I change it to "60") will it corrupt the file?
3. I precompiled one of my files and I can still see some text values in the class file. I want to hide those values so that others can't see them. Why is it showing the text as it is? Is there any way that I can resolve this?
Few linesfrom the class file looks like:
"ndError ‚
ƒ „…
† ‡ˆ ‰Š jrun/jsp/runtime/JRunPageC
rootMapClient /dpClientMap rootURL *http://192.168.0.100:8100
previewURL <http://192.168.0.100:8100
styleLink color: blue styleLinkEvenRow styleLinkOddRow styleLinkHeaderRow color: white
topBgColor #FFFFFF "
Cheers...
jspBegin,
I'll try to answer your additional question the best I can, but I'll tell before-hand, you gonna need to do some research on this...
1) No, you can't access object without having a referecnce to it. The only reason you can access the application in a JSP or a servlet is because the engine passes a refernce to it when loading the JSP or the servlet.
2) I have never tried doing that before (I'll try later today).. If I have to make a guess, I'd say yes, it is going to corrupt the class if you change the number of chars in a string literal (changing "50" to "500")... I don't about changing chars without modifing the length of the string though, like I said, must try it...
Becareful though, a string literal that shows in a class file is part of the string pool, so it might be used by more than one string object...
If you want a definite, you have to dig in the VM specifications from SUN.
3) This has been discussed a lot in many online forms. The short answer is no. The long answer is that you need to implement custom class loaders (redesign the way the VM loads classes from their files). I don't know if you have heard of java decompliers. You get one of these, give it a class file, and it will re-generate the source for you. It's one of the trade offs with java... Most people learned to accept it though (including myself).
If you just don't want the string to show clearly in the class file, try this, instead of writing:
String myStr = "ABC";
Use:
String myStr = new String( new byte[]{ 65, 66, 67 } );
Hope that helps out
No comment has been added lately, so it's time to clean up this TA.
I will leave the following recommendation for this question in the Cleanup topic area:
Accept: abuimad {http:#9023883}
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PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!
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Answer for Membership
by: rrz@871311Posted on 2003-07-28 at 11:21:40ID: 9022181
And another question is,
Will Statement3 and Statement4 be executed ?