Re: Where to catch/throw Exceptions in Struts Tiered Architecture
hi andrew and list, I have another small Q on nested exception. Consoder a nomal web scenario, where a request comes to Action, delegated to Business logic class, that class queries database and follows the path back. CustomerAction - Customer -- JDO etc. | ReqFailException DataException V ReqFailHandler global-exception | V reqfail .jsp As most(can we say All) of the requests go up to database and any method can throw exception. SO... This simple flow cleary shows that EVERY method in _JDO_ MUST be throwing DataException that CAN be *catched* by _Customer_ and consequently EVERY method in Customer WILL *throw* nested ReqFailException. PunchLine: Every method is throwing _exception_ to it's caller. Note that 2-3 methods in Customer MAY throw additional exception but ReqFailException will ALWAYS be thrown to Action class. Is that OK in normal practices? Looking forward to some replies. -Navjot Singh PS - May be i will understand it' use better if you can give me some sample code ;-) - Original Message - From: Andrew Hill [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 5:02 PM Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture Generally, returning null when it should be an error is considered bad practice. (If null is a valid return value of course thats a different matter). In this case you should throw an exception and catch it in the calling class and branch or throw again appropriately. You dont want your calling class to have to know about low level details like specific sql exceptions though, so instead of just letting the sql exception propogate upwards, you would catch it and throw a different more abstract exception (probably one you create yourself) up to the caller - the caller shouldnt have to know the details about your persistence mechanism - it just needs to know it failed - and sometimes needs to know if the failure is fatal and any other pertinent info. The nested excpetion classes should also be able to keep a reference to the exception they wrap so the stacktrace show all the exceptions in the chain - useful when debugging. btw: If I recall rightly Ted Husted explains this 10 times better in one tenth the words in his book (struts in action) Have a look at these articles: http://developer.java.sun.com/developer/technicalArticles/Programming/except ions/ http://www-106.ibm.com/developerworks/java/library/j-ejb01283.html http://www.javaworld.com/javatips/jw-javatip91_p.html There was another very good one too - but it doesnt seem to be in my favourites list and I cant seem to find it now. -Original Message- From: Navjot Singh [mailto:[EMAIL PROTECTED] Sent: Thursday, 3 April 2003 18:53 To: Struts Users Mailing List; [EMAIL PROTECTED] Subject: Re: Where to catch/throw Exceptions in Struts Tiered Architecture hi andrew, but surely these long stacktraces are not meant for users ;-) what i have got from your statement is something like this SQLException |__DatabaseException |ApplicationException finally, this ApplicationException is what is being thrown into execute() call. May i am novice, but I still need to be convinced about throwing so many exceptions in chain Can't the stuff be handled in a simple way -- SAY a. when you get SQLException, catch and return NULL b. Calling Class __ifs__ for NULL instead of __catching__ and transfer the control accordingly. Is there something i am ignoring? regards Navjot Singh - Original Message - From: Andrew Hill [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:49 PM Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture | I use nested exceptions, and virtually all my methods (and thus layers) | catch and wrap and throw... | Makes for some impressively long stacktraces - and is marvellous for | debugging! :-) | | | -Original Message- | From: Navjot Singh [mailto:[EMAIL PROTECTED] | Sent: Thursday, 3 April 2003 18:05 | To: Struts Users List | Subject: Where to catch/throw Exceptions in Struts Tiered Architecture | | | Hi, | | Take a simple case. | |Action | Y | UserAction - User - Database | | | V | user.jsp | | Say, Database throws exception. What is best way to handle exception? | | 1. Catch in User class and return NULL / some ErrorObject to UserAction and | let UserAction decide how to handle it? | | 2. Let User class __pass on__ the Exception from Database to UserAction. | | 2a. As execute() is already throwing Exception so it will handle ALL so Set | global-exception handler that can send the user to some nice page? | 2b. Catch Exception in UserAction and then do some thing ... | | Which one do you guys follow in not-so-large scale web applications
RE: Where to catch/throw Exceptions in Struts Tiered Architecture
I use nested exceptions, and virtually all my methods (and thus layers) catch and wrap and throw... Makes for some impressively long stacktraces - and is marvellous for debugging! :-) -Original Message- From: Navjot Singh [mailto:[EMAIL PROTECTED] Sent: Thursday, 3 April 2003 18:05 To: Struts Users List Subject: Where to catch/throw Exceptions in Struts Tiered Architecture Hi, Take a simple case. Action Y UserAction - User - Database | V user.jsp Say, Database throws exception. What is best way to handle exception? 1. Catch in User class and return NULL / some ErrorObject to UserAction and let UserAction decide how to handle it? 2. Let User class __pass on__ the Exception from Database to UserAction. 2a. As execute() is already throwing Exception so it will handle ALL so Set global-exception handler that can send the user to some nice page? 2b. Catch Exception in UserAction and then do some thing ... Which one do you guys follow in not-so-large scale web applications? would appreciate any comments. -navjot singh - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Where to catch/throw Exceptions in Struts Tiered Architecture
IMO, catch the database exception in user, then throw a new (wrapped) exception, catch it in UserAction and throw a new exception, and use struts decalritive exception handling features to handle it. This avoids undue coupling between UserAction, User and Database. Gareth. Navjot Singh wrote: Hi, Take a simple case. Action Y UserAction - User - Database | V user.jsp Say, Database throws exception. What is best way to handle exception? 1. Catch in User class and return NULL / some ErrorObject to UserAction and let UserAction decide how to handle it? 2. Let User class __pass on__ the Exception from Database to UserAction. 2a. As execute() is already throwing Exception so it will handle ALL so Set global-exception handler that can send the user to some nice page? 2b. Catch Exception in UserAction and then do some thing ... Which one do you guys follow in not-so-large scale web applications? would appreciate any comments. -navjot singh - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Where to catch/throw Exceptions in Struts Tiered Architecture
hi andrew, but surely these long stacktraces are not meant for users ;-) what i have got from your statement is something like this SQLException |__DatabaseException |ApplicationException finally, this ApplicationException is what is being thrown into execute() call. May i am novice, but I still need to be convinced about throwing so many exceptions in chain Can't the stuff be handled in a simple way -- SAY a. when you get SQLException, catch and return NULL b. Calling Class __ifs__ for NULL instead of __catching__ and transfer the control accordingly. Is there something i am ignoring? regards Navjot Singh - Original Message - From: Andrew Hill [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:49 PM Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture | I use nested exceptions, and virtually all my methods (and thus layers) | catch and wrap and throw... | Makes for some impressively long stacktraces - and is marvellous for | debugging! :-) | | | -Original Message- | From: Navjot Singh [mailto:[EMAIL PROTECTED] | Sent: Thursday, 3 April 2003 18:05 | To: Struts Users List | Subject: Where to catch/throw Exceptions in Struts Tiered Architecture | | | Hi, | | Take a simple case. | |Action | Y | UserAction - User - Database | | | V | user.jsp | | Say, Database throws exception. What is best way to handle exception? | | 1. Catch in User class and return NULL / some ErrorObject to UserAction and | let UserAction decide how to handle it? | | 2. Let User class __pass on__ the Exception from Database to UserAction. | | 2a. As execute() is already throwing Exception so it will handle ALL so Set | global-exception handler that can send the user to some nice page? | 2b. Catch Exception in UserAction and then do some thing ... | | Which one do you guys follow in not-so-large scale web applications? | | would appreciate any comments. | -navjot singh | | | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] | | - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Where to catch/throw Exceptions in Struts Tiered Architecture
thanks gareth, i got the point. thanks to Ted (Tip 15) and Andrew as well. -navjot - Original Message - From: Gareth Andrew [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 4:09 PM Subject: Re: Where to catch/throw Exceptions in Struts Tiered Architecture | IMO, catch the database exception in user, then throw a new (wrapped) | exception, catch it in UserAction and throw a new exception, and use | struts decalritive exception handling features to handle it. This | avoids undue coupling between UserAction, User and Database. | | Gareth. | | Navjot Singh wrote: | | Hi, | | Take a simple case. | |Action | Y | UserAction - User - Database | | | V | user.jsp | | Say, Database throws exception. What is best way to handle exception? | | 1. Catch in User class and return NULL / some ErrorObject to UserAction and | let UserAction decide how to handle it? | | 2. Let User class __pass on__ the Exception from Database to UserAction. | | 2a. As execute() is already throwing Exception so it will handle ALL so Set | global-exception handler that can send the user to some nice page? | 2b. Catch Exception in UserAction and then do some thing ... | | Which one do you guys follow in not-so-large scale web applications? | | would appreciate any comments. | -navjot singh | | | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] | | | | | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] | | - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: Where to catch/throw Exceptions in Struts Tiered Architecture
Generally, returning null when it should be an error is considered bad practice. (If null is a valid return value of course thats a different matter). In this case you should throw an exception and catch it in the calling class and branch or throw again appropriately. You dont want your calling class to have to know about low level details like specific sql exceptions though, so instead of just letting the sql exception propogate upwards, you would catch it and throw a different more abstract exception (probably one you create yourself) up to the caller - the caller shouldnt have to know the details about your persistence mechanism - it just needs to know it failed - and sometimes needs to know if the failure is fatal and any other pertinent info. The nested excpetion classes should also be able to keep a reference to the exception they wrap so the stacktrace show all the exceptions in the chain - useful when debugging. btw: If I recall rightly Ted Husted explains this 10 times better in one tenth the words in his book (struts in action) Have a look at these articles: http://developer.java.sun.com/developer/technicalArticles/Programming/except ions/ http://www-106.ibm.com/developerworks/java/library/j-ejb01283.html http://www.javaworld.com/javatips/jw-javatip91_p.html There was another very good one too - but it doesnt seem to be in my favourites list and I cant seem to find it now. -Original Message- From: Navjot Singh [mailto:[EMAIL PROTECTED] Sent: Thursday, 3 April 2003 18:53 To: Struts Users Mailing List; [EMAIL PROTECTED] Subject: Re: Where to catch/throw Exceptions in Struts Tiered Architecture hi andrew, but surely these long stacktraces are not meant for users ;-) what i have got from your statement is something like this SQLException |__DatabaseException |ApplicationException finally, this ApplicationException is what is being thrown into execute() call. May i am novice, but I still need to be convinced about throwing so many exceptions in chain Can't the stuff be handled in a simple way -- SAY a. when you get SQLException, catch and return NULL b. Calling Class __ifs__ for NULL instead of __catching__ and transfer the control accordingly. Is there something i am ignoring? regards Navjot Singh - Original Message - From: Andrew Hill [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:49 PM Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture | I use nested exceptions, and virtually all my methods (and thus layers) | catch and wrap and throw... | Makes for some impressively long stacktraces - and is marvellous for | debugging! :-) | | | -Original Message- | From: Navjot Singh [mailto:[EMAIL PROTECTED] | Sent: Thursday, 3 April 2003 18:05 | To: Struts Users List | Subject: Where to catch/throw Exceptions in Struts Tiered Architecture | | | Hi, | | Take a simple case. | |Action | Y | UserAction - User - Database | | | V | user.jsp | | Say, Database throws exception. What is best way to handle exception? | | 1. Catch in User class and return NULL / some ErrorObject to UserAction and | let UserAction decide how to handle it? | | 2. Let User class __pass on__ the Exception from Database to UserAction. | | 2a. As execute() is already throwing Exception so it will handle ALL so Set | global-exception handler that can send the user to some nice page? | 2b. Catch Exception in UserAction and then do some thing ... | | Which one do you guys follow in not-so-large scale web applications? | | would appreciate any comments. | -navjot singh | | | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] | | - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Where to catch/throw Exceptions in Struts Tiered Architecture
thanks a ton. now, i need to spend some hours doing some arrangements in my code but anyway that's for my good ;-) -navjot singh - Original Message - From: Andrew Hill [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 5:02 PM Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture | Generally, returning null when it should be an error is considered bad | practice. (If null is a valid return value of course thats a different | matter). | In this case you should throw an exception and catch it in the calling class | and branch or throw again appropriately. | You dont want your calling class to have to know about low level details | like specific sql exceptions though, so instead of just letting the sql | exception propogate upwards, you would catch it and throw a different more | abstract exception (probably one you create yourself) up to the caller - the | caller shouldnt have to know the details about your persistence mechanism - | it just needs to know it failed - and sometimes needs to know if the failure | is fatal and any other pertinent info. | The nested excpetion classes should also be able to keep a reference to the | exception they wrap so the stacktrace show all the exceptions in the chain - | useful when debugging. | | btw: If I recall rightly Ted Husted explains this 10 times better in one | tenth the words in his book (struts in action) | | Have a look at these articles: | http://developer.java.sun.com/developer/technicalArticles/Programming/except | ions/ | http://www-106.ibm.com/developerworks/java/library/j-ejb01283.html | http://www.javaworld.com/javatips/jw-javatip91_p.html | | There was another very good one too - but it doesnt seem to be in my | favourites list and I cant seem to find it now. | | | -Original Message- | From: Navjot Singh [mailto:[EMAIL PROTECTED] | Sent: Thursday, 3 April 2003 18:53 | To: Struts Users Mailing List; [EMAIL PROTECTED] | Subject: Re: Where to catch/throw Exceptions in Struts Tiered | Architecture | | | hi andrew, | | but surely these long stacktraces are not meant for users ;-) | | what i have got from your statement is something like this | | SQLException | |__DatabaseException | |ApplicationException | | finally, this ApplicationException is what is being thrown into execute() | call. | | May i am novice, but I still need to be convinced about throwing so many | exceptions in chain | | Can't the stuff be handled in a simple way -- | SAY | a. when you get SQLException, catch and return NULL | b. Calling Class __ifs__ for NULL instead of __catching__ and transfer the | control accordingly. | | Is there something i am ignoring? | | regards | Navjot Singh | | - Original Message - | From: Andrew Hill [EMAIL PROTECTED] | To: Struts Users Mailing List [EMAIL PROTECTED] | Sent: Thursday, April 03, 2003 3:49 PM | Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture | | | | I use nested exceptions, and virtually all my methods (and thus layers) | | catch and wrap and throw... | | Makes for some impressively long stacktraces - and is marvellous for | | debugging! :-) | | | | | | -Original Message- | | From: Navjot Singh [mailto:[EMAIL PROTECTED] | | Sent: Thursday, 3 April 2003 18:05 | | To: Struts Users List | | Subject: Where to catch/throw Exceptions in Struts Tiered Architecture | | | | | | Hi, | | | | Take a simple case. | | | |Action | | Y | | UserAction - User - Database | | | | | V | | user.jsp | | | | Say, Database throws exception. What is best way to handle exception? | | | | 1. Catch in User class and return NULL / some ErrorObject to UserAction | and | | let UserAction decide how to handle it? | | | | 2. Let User class __pass on__ the Exception from Database to UserAction. | | | | 2a. As execute() is already throwing Exception so it will handle ALL so | Set | | global-exception handler that can send the user to some nice page? | | 2b. Catch Exception in UserAction and then do some thing ... | | | | Which one do you guys follow in not-so-large scale web applications? | | | | would appreciate any comments. | | -navjot singh | | | | | | | | | | - | | To unsubscribe, e-mail: [EMAIL PROTECTED] | | For additional commands, e-mail: [EMAIL PROTECTED] | | | | | | - | | To unsubscribe, e-mail: [EMAIL PROTECTED] | | For additional commands, e-mail: [EMAIL PROTECTED] | | | | | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED
RE: Where to catch/throw Exceptions in Struts Tiered Architecture
Since you guys are having a good discussion on the exceptions handling in Struts, I would like to ask a lower level question on this topic. On my JSP I always get a null exception something like [Exception on \myPage.jsp: null]. At the beginning this exception was very frustrating since no more details were showing. Now I konw in 90% of the cases, this exception is from one of the taglibraries. But question is how I can get more informative details without having a try/catch block on my jsps. Regards, Erica -Original Message- From: Andrew Hill [mailto:[EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:33 AM To: Struts Users Mailing List Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture Generally, returning null when it should be an error is considered bad practice. (If null is a valid return value of course thats a different matter). In this case you should throw an exception and catch it in the calling class and branch or throw again appropriately. You dont want your calling class to have to know about low level details like specific sql exceptions though, so instead of just letting the sql exception propogate upwards, you would catch it and throw a different more abstract exception (probably one you create yourself) up to the caller - the caller shouldnt have to know the details about your persistence mechanism - it just needs to know it failed - and sometimes needs to know if the failure is fatal and any other pertinent info. The nested excpetion classes should also be able to keep a reference to the exception they wrap so the stacktrace show all the exceptions in the chain - useful when debugging. btw: If I recall rightly Ted Husted explains this 10 times better in one tenth the words in his book (struts in action) Have a look at these articles: http://developer.java.sun.com/developer/technicalArticles/Programming/except ions/ http://www-106.ibm.com/developerworks/java/library/j-ejb01283.html http://www.javaworld.com/javatips/jw-javatip91_p.html There was another very good one too - but it doesnt seem to be in my favourites list and I cant seem to find it now. -Original Message- From: Navjot Singh [mailto:[EMAIL PROTECTED] Sent: Thursday, 3 April 2003 18:53 To: Struts Users Mailing List; [EMAIL PROTECTED] Subject: Re: Where to catch/throw Exceptions in Struts Tiered Architecture hi andrew, but surely these long stacktraces are not meant for users ;-) what i have got from your statement is something like this SQLException |__DatabaseException |ApplicationException finally, this ApplicationException is what is being thrown into execute() call. May i am novice, but I still need to be convinced about throwing so many exceptions in chain Can't the stuff be handled in a simple way -- SAY a. when you get SQLException, catch and return NULL b. Calling Class __ifs__ for NULL instead of __catching__ and transfer the control accordingly. Is there something i am ignoring? regards Navjot Singh - Original Message - From: Andrew Hill [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:49 PM Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture | I use nested exceptions, and virtually all my methods (and thus layers) | catch and wrap and throw... | Makes for some impressively long stacktraces - and is marvellous for | debugging! :-) | | | -Original Message- | From: Navjot Singh [mailto:[EMAIL PROTECTED] | Sent: Thursday, 3 April 2003 18:05 | To: Struts Users List | Subject: Where to catch/throw Exceptions in Struts Tiered Architecture | | | Hi, | | Take a simple case. | |Action | Y | UserAction - User - Database | | | V | user.jsp | | Say, Database throws exception. What is best way to handle exception? | | 1. Catch in User class and return NULL / some ErrorObject to UserAction and | let UserAction decide how to handle it? | | 2. Let User class __pass on__ the Exception from Database to UserAction. | | 2a. As execute() is already throwing Exception so it will handle ALL so Set | global-exception handler that can send the user to some nice page? | 2b. Catch Exception in UserAction and then do some thing ... | | Which one do you guys follow in not-so-large scale web applications? | | would appreciate any comments. | -navjot singh | | | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] | | - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] - To unsubscribe, e-mail: [EMAIL
RE: Where to catch/throw Exceptions in Struts Tiered Architecture
I think the null is generated because the exception's message String was set to null. It's helped me to print out the various scopes' attributes at the bottom of the page because the exceptions show up in there. David From: Erica Leung [EMAIL PROTECTED] Reply-To: Struts Users Mailing List [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture Date: Thu, 3 Apr 2003 11:08:56 -0800 Since you guys are having a good discussion on the exceptions handling in Struts, I would like to ask a lower level question on this topic. On my JSP I always get a null exception something like [Exception on \myPage.jsp: null]. At the beginning this exception was very frustrating since no more details were showing. Now I konw in 90% of the cases, this exception is from one of the taglibraries. But question is how I can get more informative details without having a try/catch block on my jsps. Regards, Erica -Original Message- From: Andrew Hill [mailto:[EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:33 AM To: Struts Users Mailing List Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture Generally, returning null when it should be an error is considered bad practice. (If null is a valid return value of course thats a different matter). In this case you should throw an exception and catch it in the calling class and branch or throw again appropriately. You dont want your calling class to have to know about low level details like specific sql exceptions though, so instead of just letting the sql exception propogate upwards, you would catch it and throw a different more abstract exception (probably one you create yourself) up to the caller - the caller shouldnt have to know the details about your persistence mechanism - it just needs to know it failed - and sometimes needs to know if the failure is fatal and any other pertinent info. The nested excpetion classes should also be able to keep a reference to the exception they wrap so the stacktrace show all the exceptions in the chain - useful when debugging. btw: If I recall rightly Ted Husted explains this 10 times better in one tenth the words in his book (struts in action) Have a look at these articles: http://developer.java.sun.com/developer/technicalArticles/Programming/except ions/ http://www-106.ibm.com/developerworks/java/library/j-ejb01283.html http://www.javaworld.com/javatips/jw-javatip91_p.html There was another very good one too - but it doesnt seem to be in my favourites list and I cant seem to find it now. -Original Message- From: Navjot Singh [mailto:[EMAIL PROTECTED] Sent: Thursday, 3 April 2003 18:53 To: Struts Users Mailing List; [EMAIL PROTECTED] Subject: Re: Where to catch/throw Exceptions in Struts Tiered Architecture hi andrew, but surely these long stacktraces are not meant for users ;-) what i have got from your statement is something like this SQLException |__DatabaseException |ApplicationException finally, this ApplicationException is what is being thrown into execute() call. May i am novice, but I still need to be convinced about throwing so many exceptions in chain Can't the stuff be handled in a simple way -- SAY a. when you get SQLException, catch and return NULL b. Calling Class __ifs__ for NULL instead of __catching__ and transfer the control accordingly. Is there something i am ignoring? regards Navjot Singh - Original Message - From: Andrew Hill [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:49 PM Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture | I use nested exceptions, and virtually all my methods (and thus layers) | catch and wrap and throw... | Makes for some impressively long stacktraces - and is marvellous for | debugging! :-) | | | -Original Message- | From: Navjot Singh [mailto:[EMAIL PROTECTED] | Sent: Thursday, 3 April 2003 18:05 | To: Struts Users List | Subject: Where to catch/throw Exceptions in Struts Tiered Architecture | | | Hi, | | Take a simple case. | |Action | Y | UserAction - User - Database | | | V | user.jsp | | Say, Database throws exception. What is best way to handle exception? | | 1. Catch in User class and return NULL / some ErrorObject to UserAction and | let UserAction decide how to handle it? | | 2. Let User class __pass on__ the Exception from Database to UserAction. | | 2a. As execute() is already throwing Exception so it will handle ALL so Set | global-exception handler that can send the user to some nice page? | 2b. Catch Exception in UserAction and then do some thing ... | | Which one do you guys follow in not-so-large scale web applications? | | would appreciate any comments. | -navjot singh | | | | | - | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL
RE: Where to catch/throw Exceptions in Struts Tiered Architecture
Is there any plug I can set up the exception's message, so I can know at least which tag throws an exception? -Erica -Original Message- From: David Graham [mailto:[EMAIL PROTECTED] Sent: Thursday, April 03, 2003 11:21 AM To: [EMAIL PROTECTED] Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture I think the null is generated because the exception's message String was set to null. It's helped me to print out the various scopes' attributes at the bottom of the page because the exceptions show up in there. David From: Erica Leung [EMAIL PROTECTED] Reply-To: Struts Users Mailing List [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture Date: Thu, 3 Apr 2003 11:08:56 -0800 Since you guys are having a good discussion on the exceptions handling in Struts, I would like to ask a lower level question on this topic. On my JSP I always get a null exception something like [Exception on \myPage.jsp: null]. At the beginning this exception was very frustrating since no more details were showing. Now I konw in 90% of the cases, this exception is from one of the taglibraries. But question is how I can get more informative details without having a try/catch block on my jsps. Regards, Erica -Original Message- From: Andrew Hill [mailto:[EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:33 AM To: Struts Users Mailing List Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture Generally, returning null when it should be an error is considered bad practice. (If null is a valid return value of course thats a different matter). In this case you should throw an exception and catch it in the calling class and branch or throw again appropriately. You dont want your calling class to have to know about low level details like specific sql exceptions though, so instead of just letting the sql exception propogate upwards, you would catch it and throw a different more abstract exception (probably one you create yourself) up to the caller - the caller shouldnt have to know the details about your persistence mechanism - it just needs to know it failed - and sometimes needs to know if the failure is fatal and any other pertinent info. The nested excpetion classes should also be able to keep a reference to the exception they wrap so the stacktrace show all the exceptions in the chain - useful when debugging. btw: If I recall rightly Ted Husted explains this 10 times better in one tenth the words in his book (struts in action) Have a look at these articles: http://developer.java.sun.com/developer/technicalArticles/Programming/excep t ions/ http://www-106.ibm.com/developerworks/java/library/j-ejb01283.html http://www.javaworld.com/javatips/jw-javatip91_p.html There was another very good one too - but it doesnt seem to be in my favourites list and I cant seem to find it now. -Original Message- From: Navjot Singh [mailto:[EMAIL PROTECTED] Sent: Thursday, 3 April 2003 18:53 To: Struts Users Mailing List; [EMAIL PROTECTED] Subject: Re: Where to catch/throw Exceptions in Struts Tiered Architecture hi andrew, but surely these long stacktraces are not meant for users ;-) what i have got from your statement is something like this SQLException |__DatabaseException |ApplicationException finally, this ApplicationException is what is being thrown into execute() call. May i am novice, but I still need to be convinced about throwing so many exceptions in chain Can't the stuff be handled in a simple way -- SAY a. when you get SQLException, catch and return NULL b. Calling Class __ifs__ for NULL instead of __catching__ and transfer the control accordingly. Is there something i am ignoring? regards Navjot Singh - Original Message - From: Andrew Hill [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:49 PM Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture | I use nested exceptions, and virtually all my methods (and thus layers) | catch and wrap and throw... | Makes for some impressively long stacktraces - and is marvellous for | debugging! :-) | | | -Original Message- | From: Navjot Singh [mailto:[EMAIL PROTECTED] | Sent: Thursday, 3 April 2003 18:05 | To: Struts Users List | Subject: Where to catch/throw Exceptions in Struts Tiered Architecture | | | Hi, | | Take a simple case. | |Action | Y | UserAction - User - Database | | | V | user.jsp | | Say, Database throws exception. What is best way to handle exception? | | 1. Catch in User class and return NULL / some ErrorObject to UserAction and | let UserAction decide how to handle it? | | 2. Let User class __pass on__ the Exception from Database to UserAction. | | 2a. As execute() is already throwing Exception so it will handle ALL so Set | global-exception handler that can send the user to some nice page? | 2b. Catch
RE: Where to catch/throw Exceptions in Struts Tiered Architecture
The exception message is set when the exeption object is created so you can't set it. I've found it helpful to display the attributes because you can see the exception in there. Other than that, it's the old fashioned comment-out-code-until-it-works method. David From: Erica Leung [EMAIL PROTECTED] Reply-To: Struts Users Mailing List [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture Date: Thu, 3 Apr 2003 11:37:58 -0800 Is there any plug I can set up the exception's message, so I can know at least which tag throws an exception? -Erica -Original Message- From: David Graham [mailto:[EMAIL PROTECTED] Sent: Thursday, April 03, 2003 11:21 AM To: [EMAIL PROTECTED] Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture I think the null is generated because the exception's message String was set to null. It's helped me to print out the various scopes' attributes at the bottom of the page because the exceptions show up in there. David From: Erica Leung [EMAIL PROTECTED] Reply-To: Struts Users Mailing List [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture Date: Thu, 3 Apr 2003 11:08:56 -0800 Since you guys are having a good discussion on the exceptions handling in Struts, I would like to ask a lower level question on this topic. On my JSP I always get a null exception something like [Exception on \myPage.jsp: null]. At the beginning this exception was very frustrating since no more details were showing. Now I konw in 90% of the cases, this exception is from one of the taglibraries. But question is how I can get more informative details without having a try/catch block on my jsps. Regards, Erica -Original Message- From: Andrew Hill [mailto:[EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:33 AM To: Struts Users Mailing List Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture Generally, returning null when it should be an error is considered bad practice. (If null is a valid return value of course thats a different matter). In this case you should throw an exception and catch it in the calling class and branch or throw again appropriately. You dont want your calling class to have to know about low level details like specific sql exceptions though, so instead of just letting the sql exception propogate upwards, you would catch it and throw a different more abstract exception (probably one you create yourself) up to the caller - the caller shouldnt have to know the details about your persistence mechanism - it just needs to know it failed - and sometimes needs to know if the failure is fatal and any other pertinent info. The nested excpetion classes should also be able to keep a reference to the exception they wrap so the stacktrace show all the exceptions in the chain - useful when debugging. btw: If I recall rightly Ted Husted explains this 10 times better in one tenth the words in his book (struts in action) Have a look at these articles: http://developer.java.sun.com/developer/technicalArticles/Programming/excep t ions/ http://www-106.ibm.com/developerworks/java/library/j-ejb01283.html http://www.javaworld.com/javatips/jw-javatip91_p.html There was another very good one too - but it doesnt seem to be in my favourites list and I cant seem to find it now. -Original Message- From: Navjot Singh [mailto:[EMAIL PROTECTED] Sent: Thursday, 3 April 2003 18:53 To: Struts Users Mailing List; [EMAIL PROTECTED] Subject: Re: Where to catch/throw Exceptions in Struts Tiered Architecture hi andrew, but surely these long stacktraces are not meant for users ;-) what i have got from your statement is something like this SQLException |__DatabaseException |ApplicationException finally, this ApplicationException is what is being thrown into execute() call. May i am novice, but I still need to be convinced about throwing so many exceptions in chain Can't the stuff be handled in a simple way -- SAY a. when you get SQLException, catch and return NULL b. Calling Class __ifs__ for NULL instead of __catching__ and transfer the control accordingly. Is there something i am ignoring? regards Navjot Singh - Original Message - From: Andrew Hill [EMAIL PROTECTED] To: Struts Users Mailing List [EMAIL PROTECTED] Sent: Thursday, April 03, 2003 3:49 PM Subject: RE: Where to catch/throw Exceptions in Struts Tiered Architecture | I use nested exceptions, and virtually all my methods (and thus layers) | catch and wrap and throw... | Makes for some impressively long stacktraces - and is marvellous for | debugging! :-) | | | -Original Message- | From: Navjot Singh [mailto:[EMAIL PROTECTED] | Sent: Thursday, 3 April 2003 18:05 | To: Struts Users List | Subject: Where to catch/throw Exceptions in Struts Tiered Architecture | | | Hi, | | Take a simple
