Exception handling-Design issue -Very interesting

Hello developers
An argument been arised and i would like your opinon=:
a jsp jas the following code:
String x=request.getParamater("id");
int t-Integer.parseInt(x);
Now as you can see the parsing is not in try{}catch block ,thus
a NumberFormatException is not catched in the page .
But a developer has written an error page that all exceptions are thrown there .this means that althought we dont know from which page the error accured (unless we printStackTrace()) we are catching the exception in a more global way but the handling is somewhat bad.
please tell me your opinions.is it enough to let the error page catch it or we should catch it in the page and then having control over the exception we can decide what to do with it?
regards
yoav

some one?

Similar Messages

Exception handling design issue

I have a class that's a low level building block of my application. It takes as its single constructor argument a String that needs to be in a known format. At present the constructor takes this String and checks it, throwing an Exception if it's not in the expected format. Given that the String can be built up from user sourced data, this check is absolutely required.
The problem is that 95% of the time I build these objects using well known Strings - frequently constants from my code. In these cases I don't need the check. That's not really the issue - the checks don't cost a great deal. The problem is the Exception: each time I want to create one of these objects I have to handle the exception I know is never going to happen. I now have dozens of try/catch's in my code that just wrap a call to the constructor and have an empty catch block because I know that's never going to go wrong and I just want to shut the complier up.
This can't be the right way to do it! I don't want to take out the String check entirely, and I do need the safety net of the Exception in some cases, but without the hassle it provides so much of the time. How should I change the design of this class so that I get the balance I want?

new Foo(Bar.DEFAULT_BAR_1); //without try-catch
//or
new Foo(new Bar("blublab")); //requires try-catchHmm, maybe I haven't quite got this sussed yet.
The nature of my String value is a location - like a URI. My application is full of them. A good number of them are known at compile time and can be defined and used as constants by the code that needs them, but the underlying class needs to be able deal with user supplied strings as well.
I define a class called Location which used to have a single constructor that took a String. If the String was of the wrong format it threw an Exception, but in most cases I know what I'm passing and I know it's valid. That makes the Exception, and associated try/catch, redundant 95% of the time.
So I added another constructor: the original still takes a String and throws the exception, and the new one takes a String and a dontCheck flag and doesn't throw anything. This new constructor doesn't do the format check - things will go wrong if an invalid String is passed into this constructor. In principle this works as long as I stick to the rule - only use the constructor with the dontCheck flag when I know the String I'm passing is valid. But it feels like a bug waiting to happen.
If I understood correctly, your suggestion was to create a new class - let's call it ValidatedPath. Now I can change my Location's constructors:
public Location( ValidatedPath trustedPath )
public Location( String untrustedPath ) throws LocationException
...This looks good - I can't create a ValidatedPath without getting an error, so that Location constructor doesn't need to throw anything.
But hang on - all I've done is move the problem back a step. When I create a ValidatedPath from a constant, I still need to handle the exception the ValidatedPath constructor will throw if it's given an invalid path:
public static final String goodPath = "THIS:IS:A:GOOD:VALUE";
ValidatedPath vp = new ValidatedPath( goodPath ); // I now need to handle the potential exception here...
Location l = new Location(vp); // ...instead of hereIn the above snippet, goodPath is a valid, constant path. But when I use it as an argument to the ValidatedPath constructor I still need to wrap the call in a try/catch because the ValidatedPath constructor still needs to be able to throw an Exception if the argument is invalid. I haven't really achieved anything.
Puzzlement continues. I'm just looking at your use of the IllegalArgumentException, as also suggested by others. I think I need to understand this concept of "unchecked" properly - maybe that's the key.

ADF Task Flow Exception Handling

Hi ,
I tried a very simple thing for taskFlow exception handling.
I created a bounded task flow with a page fragment (View1.jsff) and another view which is the TaskFlow ExceptionHandler (error.jsff).
The view1.jsff has a button whose action is bound to the backing bean. In the backingBean method I deliberately do division by 0.
Since this is an unHandled exception, I would have expected the control to come to error.jsff. But, instead I am shown a pop up box with the error message.
Why is the control not getting redirected to error.jsff ?
Thanks.
S.Srivatsa Sivan

Hi Frank , im having the same problem.
I want to handle exceptions that occur while navigating task flows (example: A user navigates to a task flow that he/she does not have view permission)
I tried using a view activity and method activity as the exception handler but none of them works, the exception is still not handles. It does not even navigate to the exception handler on the task flow.
on the view page i have:
<af:panelStretchLayout topHeight="50px" id="psl1">
<f:facet name="top">
<af:panelGroupLayout layout="scroll"
xmlns:af="http://xmlns.oracle.com/adf/faces/rich"
id="pgl1">
Error message:
<af:outputText value="#{controllerContext.currentRootViewPort.exceptionData.message}" id="ot2"/>
</af:panelGroupLayout>
</f:facet>
<f:facet name="center">
<af:outputText value="#{my_exception_Handler.stackTrace}" id="ot1"/>

</f:facet>
</af:panelStretchLayout>
I tried getting the error message and stacktrace from the controllerContext via EL like this "#{controllerContext.currentRootViewPort.exceptionData.message}"
and from the controllerContext class in functions that i have declared in my_exception_Handler class like this
" ControllerContext ctx = ControllerContext.getInstance();
ViewPortContext vCtx = ctx.getCurrentViewPort();
if(vCtx.getExceptionData() != null){
StringWriter stringWriter = new StringWriter();
PrintWriter printWriter = new PrintWriter(stringWriter);
vCtx.getExceptionData().printStackTrace(printWriter);
return stringWriter.toString();"
But all this dont even matter because when the exception occurs on the task flow it does not navigate to the default exception handler.
thanks for your interest and help in advance.
Cyborg_0912

Issue with exception Handling in GG

Hi,
I have bi-directional DML replication setup. I have written a code in replication parameter for handling the exception , Exception handling is working fine my replicate process is not getting ABENDED but Issue is I am not geeting any rows in EXCEPTION table.I had gone through replicat report, there I had seen GG is trying to inser duplicate records in EXCEPTION TABLE and it is failing because of that .
**Command for create Exception Table is-**
create table ggs_admin.exceptions (
rep_name      varchar2(8) ,
table_name      varchar2(61) ,
errno      number ,
dberrmsg      varchar2(4000) ,
optype               varchar2(20) ,
errtype           varchar2(20) ,
logrba               number ,
logposition          number ,
committimestamp      timestamp,
CONSTRAINT pk_exceptions PRIMARY KEY (logrba, logposition, committimestamp)
USING INDEX
TABLESPACE INDX1
TABLESPACE dbdat1
My replication parameter is-
GGSCI (db) 1> view params rep2
-- Replicator parameter file to apply changes
REPLICAT rep2
ASSUMETARGETDEFS
USERID ggs_admin, PASSWORD ggs_admin
DISCARDFILE /u01/app/oracle/product/gg/dirdat/rep2_discard.dsc, PURGE
-- Start of the macro
MACRO #exception_handler
BEGIN
, TARGET ggs_admin.exceptions
, COLMAP ( rep_name = "REP2"
, table_name = @GETENV ("GGHEADER", "TABLENAME")
, errno = @GETENV ("LASTERR", "DBERRNUM")
, dberrmsg = @GETENV ("LASTERR", "DBERRMSG")
, optype = @GETENV ("LASTERR", "OPTYPE")
, errtype = @GETENV ("LASTERR", "ERRTYPE")
, logrba = @GETENV ("GGHEADER", "LOGRBA")
, logposition = @GETENV ("GGHEADER", "LOGPOSITION")
, committimestamp = @GETENV ("GGHEADER", "COMMITTIMESTAMP"))
, INSERTALLRECORDS
, EXCEPTIONSONLY;
END;
-- End of the macro
REPERROR (DEFAULT, EXCEPTION)
--REPERROR (-1, EXCEPTION)
--REPERROR (-1403, EXCEPTION)
MAP scr.order_items, TARGET scr.order_items;
MAP scr.order_items #exception_handler();
GGSCI (db) 2>view params rep2
MAP resolved (entry scr.order_items):
MAP "scr"."order_items" TARGET ggs_admin.exceptions , COLMAP ( rep_name = "REP2" , table_name = @GETENV ("GGHEADER", "TABLENAME") , errno = @GETENV ("LASTERR", "DB
ERRNUM") , dberrmsg = @GETENV ("LASTERR", "DBERRMSG") , optype = @GETENV ("LASTERR", "OPTYPE") , errtype = @GETENV ("LASTERR", "ERRTYPE") , logrba = @GETENV ("GGHEADER"
, "LOGRBA") , logposition = @GETENV ("GGHEADER", "LOGPOSITION") , committimestamp = @GETENV ("GGHEADER", "COMMITTIMESTAMP")) , INSERTALLRECORDS , EXCEPTIONSONLY;;
Using the following key columns for target table GGS_ADMIN.EXCEPTIONS: LOGRBA, LOGPOSITION, COMMITTIMESTAMP.
2012-08-30 09:09:00 WARNING OGG-01154 SQL error 1403 mapping scr.order_items to scr.order_items OCI Error ORA-01403: no data found, SQL <DELETE FROM "scr"."order_items" WHERE "SUBSCRIBER_ID" = :b0>.
2012-08-30 09:09:00 WARNING OGG-00869 OCI Error ORA-00001: unique constraint (GGS_ADMIN.PK_EXCEPTIONS) violated (status = 1). INSERT INTO "GGS_ADMIN"."EXCEPTIONS" ("R
EP_NAME","TABLE_NAME","ERRNO","DBERRMSG","OPTYPE","ERRTYPE","LOGRBA","LOGPOSITION","COMMITTIMESTAMP") VALUES (:a0,:a1,:a2,:a3,:a4,:a5,:a6,:a7,:a8).
2012-08-30 09:09:00 WARNING OGG-01004 Aborted grouped transaction on 'GGS_ADMIN.EXCEPTIONS', Database error 1 (OCI Error ORA-00001: unique constraint (GGS_ADMIN.PK_EX
CEPTIONS) violated (status = 1). INSERT INTO "GGS_ADMIN"."EXCEPTIONS" ("REP_NAME","TABLE_NAME","ERRNO","DBERRMSG","OPTYPE","ERRTYPE","LOGRBA","LOGPOSITION","COMMITTIMES
TAMP") VALUES (:a0,:a1,:a2,:a3,:a4,:a5,:a6,:a7,:a8)).
2012-08-30 09:09:00 WARNING OGG-01003 Repositioning to rba 92383 in seqno 8.
2012-08-30 09:09:00 WARNING OGG-01154 SQL error 1403 mapping scr.order_items to scr.order_items OCI Error ORA-01403: no data found, SQL <DELETE FROM "scr"."order_items" WHERE "SUBSCRIBER_ID" = :b0>.
2012-08-30 09:09:00 WARNING OGG-01154 SQL error 1 mapping scr.order_items to GGS_ADMIN.EXCEPTIONS OCI Error ORA-00001: unique constraint (GGS_ADMIN.PK_EXCEPTIONS)
violated (status = 1). INSERT INTO "GGS_ADMIN"."EXCEPTIONS" ("REP_NAME","TABLE_NAME","ERRNO","DBERRMSG","OPTYPE","ERRTYPE","LOGRBA","LOGPOSITION","COMMITTIMESTAMP") VAL
UES (:a0,:a1,:a2,:a3,:a4,:a5,:a6,:a7,:a8).
2012-08-30 09:09:00 WARNING OGG-01003 Repositioning to rba 92383 in seqno 8.
When I am running command
select * from exceptions;
no row selected.
Please help. Why duplicat rows trying to insert in Exception table.

Remove (disable) the constraint on the exceptions table and see if inserts will take place. Do you really need that primary key?

BPM Process - Exception handling or timeout issues?

Hi Guys,
I have a BPM process as below.
1. Receive step: Receive the file with multiple transactions.
2. Transformation step: Split the file into individual transactions
3 Block step which includes -- par for each mode
1. Send Step (Synchronus): Each individual transaction needs to contact the 3rd party system and get the response. -- Do i need to handle any exceptions here ?
2. Container : Collect all the responses
Block ends
4. Transformation: combine all the responses in to a single file
5. Send Step: synchronus -- send the above single file and get the response back
6. Transformation : Transform the above response into the target structure.
7. Send: send the message asynchronusly to the target system
I need suggestion regarding the exceptional handling or any time out issues, i need to take care of.
any suggestions would be really appreciated
Thanks,
Raj
Edited by: raj reddy on Feb 12, 2009 10:12 PM

Hi,
I) For the Block holding the Sync Send, create an Exception Block. (right click on Sync Send -> Insert -> Exception Branch)
II) Name the Exception block (ex: exceptionHandler).
III) in the Sync Send step ->Properties -> Exceptions -> in System Error - add exceptionHandler.
IV) Now within the Exception handler block you can create containers to hold values from payload, throw exception as email etc).
This will cover your sync send step incase there is an error while sending the request of a timeout during receiving the response.
You can also do the same for the Step 7) Asycn send - if required.
Another suggestion in your question Step 6) can be done outside the bpm, when you do the interface determination for that Asycn Send you can add the Interface mapping that will map the responses to the target structure.
Doing this will reduce one step in your BPM. For further information in how more you can fine tune your bpm, read this blog - https://www.sdn.sap.com/irj/scn/weblogs?blog=/pub/wlg/5113. [original link is broken] [original link is broken] [original link is broken]
All the best.
Regards,
Balaji.M

Exception Handling in Object Oriented Design

I am developing a huge web based project using Object Oriented design and java,srvlets ,jsp etc ,I am using 3-tier archtecture.I dont understand,how i should handle exceptions in my project.ie.If there is some exception in the base modules how should it be handled.What kind of excpetion Structure should i use,How many exception classes should be made etc,
Can someone help me in this regard

A couple things I have found to be good practices for exception handling in an n-tier architecture:
1. Don't expose all the internal exceptions of a tier to the client of the tier. Create a more useful, descriptive set of exceptions (or use the appropriate predefined exceptions) to throw up to the client.
For example, on one project, we are doing database access among other things in the "service" tier, which is accessed by the web tier. We catch the SQLExceptions, PersistenceExceptions (a custom exception), and others, and throw a more useful exception that the client will know how to handle such as a NoMeasurementResultsException if the client asks for measurement results when we have none.
2. Chain your exceptions and/or log the root cause in the tier that re-throws a different exception. There is nothing more aggravating than not knowing why, when you are debugging a problem, you are getting a NoMeasurementResultsException when you know that there ARE results in the database.
Hope these ideas help in your design.
Cheers,
Colin

I am just starting out in graphic design and I wanted to know how to get more involved with either adobe and or graphic design? I am really very interested in working with adobe and graphic design more and becoming more involved with both!!

I am just starting out in graphic design and I wanted to know how to get more involved with either adobe and or graphic design? I am really very interested in working with adobe and graphic design more and becoming more involved with both!!

I have now recently downloaded 10.0.2 which is confusing in itself, as, as far as I can ascertain that is actually version 11, but I'm not even sure about that.
Version 10.0.2 is the newest version and the successor to GarageBand '11 (version 6.0.5).
The '11 is referring to the iLife '11 suit of multimedia application - the older GarageBand was a part of this bundle.
Have a look at Edgar's graphical enhanced manuals, the explain very detailed how things work and why. You can buy them as iBooks from the iBook store or directly from the page:
http://DingDingMusic.com/Manuals/

I bought and legally own PS CS3. Installed on a desktop and the machine died completely. Downloaded a trial of CS3 from Adobe site. Went to activate and said too many activations. Activate over the phone. EXCEPT Adobe does not handle activation issues ove

I bought and legally own PS CS3. Installed on a desktop and the machine died completely. Downloaded a trial of CS3 from Adobe site. Went to activate and said too many activations. Activate over the phone. EXCEPT Adobe does not handle activation issues over the phone. Adobe doesn't care about their older products - they don't care that I spent hundreds of dollars for CS3. This is truly disgusting corporate behavior. Is there anything I can do? We aren't all rich photographers. I paid a great deal of money for this product. Is it now useless?Thank you,
James Scott

HI James please contact the Adobe Chat Team for activation issue
kindly do the mentioned steps as follow in order to get hold of chat rep of adobe
Go to www.adobe.com/getsupport
select the product as adobe creative suite - then select the issue as adobe id and sign in - and then click on still need help contact us then you will be able to find chat option and they will help you with the chat issue

Exception handling issue

I have a perplexing question.... I am in the midst of developing an APEX 4.0 application. Customer will NOT be going to4.1 for a while....I wish to have exception handling that will handle both APEX based interactions and some back-end Sql Loader activity.
I have built an Exception handler that has a supporting APEX page to display a more human compatible error page, but am trying to make the exception handler NOT try and call up a page and such if the exception it encounters is a trigger being fired when a # of rows are being bulked loaded..
Simply put.. In the exception handler, how can I have code branch around the fact I might NOT have an APEX application for it to display the error ...
What I'd love to find is an object or variable that tells me what I am running the PL/SQL under..
Thank you,
Tony Miller
Dallas, Tx

Jari,
If I try running this from SQL Plus, I would assume it would crash due to fact I am NOT running under APEX and can NOT see the Application object that this function is based upon:
IS_SESSION_VALID Function
This function is a Boolean result obtained from executing the current application's authentication scheme to determine if a valid session exists. This function returns the Boolean result of the authentication scheme's page sentry.
Its like trying to figure out which came 1st, the chicken or the egg...
Thank you,
Tony Miller
Dallas, TX

Very simple exception handling

I know next to nothing about exceptions, I am still only in 3rd week of class, but I already ran into one.
I was using the Scanner Class, and the nextInt() function (method ?) to get some numbers to do simple math on. Program worked fine. But if I put a letter in when it asks for a number, it crashs to commandline with exception error. I just added text that told the user only to put in the right var type. Integers in this case. How would I make an exception handler ? is that right, exception handler ? that would simply say "wrong data type, please reenter", then ask again ? or something ?
Getting used to the forum here, bit different than I'm used to. Hope my question was clear.

ok, I scanned through all and read thoroughly some of that. I have been working my way through the series as I can. we will be covering this in some detail later in the semester. That article (chapter?) is great, but it is too broad for me right now, I will post some code, and add some comments that try to do some of what I got from that article.
This is a stupid hello world type thing idid, we had worked with Scanner nextInt(), but not Scanner next, so I looked up how to get strings on my own... first week first prog i did anything on besides follow along :)
// Java Document
import java.util.Scanner; // uses Scanner Class
public class sparkle     //main method
     public static void main( String args[] )
          Scanner input = new Scanner( System.in );
          String name;
//so here I would add a try statement ?
          System.out.print( "Enter Your Name:" );
          name = input.next();
          // and end it here ?
          System.out.printf( "%s\t%s\t%s\n\t\t%s",
          "***", "Java Programming!", "***", name);
// then I would put a catch here ? that tested to see if it was a string ?
//and if not then what ?
}maybe that is a bad example... I get that you have to wrap a block of code in a try statement, then you put catch statements, that see if the can do something about watever exception it is, but what do they do, the examples in that article use stuff way past where I am now... libraries I'm not familiar with to know what is happening. What does finally do ? what should happen instead, or what should happen either way ? I will go over more of that article, but most of it is meant to be read after I am further along... I think I am getting the basics though. Do I seem to be on the right track..?
I will post some more code about this later, I really don't expect to solve this overnight, but i know good exception handling hardens a program to faults, and provides stability. So I want to get a grasp of what to expect now. really, we wont be covering this in class for another month or two... but I want to prepare now, so I will be programming well by then.
Edited by: lord_midnight on Feb 15, 2008 4:02 PM

EJB Exception Layer Design Feedback

I am in the process of creating a EJB layer talking to EIS Tier via JCA adapter. The EJBs are all stateless. The EJBs would be used by servlets, ejbs, or jsps. The EJBs are stateless in nature. I would like to make sure the exception hierarchy I have is considered good design practice and if there are suggestions on how I may improve it. I decided to go for unchecked exception all through my design (this I don't want to change -- pretty sure about this).
So, here is how I designed my exception class. One of my goals was to keep the exception handling very simple at the client-side and not inundate customers with too many types of exceptions. I decided to go for a has-A type relationship to model much of the exceptions because I couldnt really classify some of them to be a is-A. All exceptions thrown by my EJB layer would be contained within MyApplicationException. A getCause() will give insight into the cause at a very fine level. A getMessage() would suffice for most situations. Whereever exceptions are being thrown, the cause is being stored.
java.lang.Exception
--java.lang.RuntimeException
___ --MyBaseException
_______+----MyApplicationException (this is the container for all my exceptions)
_______+----MyConfigException
I created a exceptionhelper class that handles most of the exceptions and throws the right exception depending on the cause. For brevity sake, I am not including all code details in the sample below.
At the EIS Tier level, we have AutomationExceptions or Windows exception being thrown. These exceptions get thrown by the Windows code that is running in the EIS Tier (server). These exceptions are caught by the EJB code, then we do some processing like looking up the windows error code and producing the right message. The exception is then thrown back to the client with more information (MyApplicationException->getCause() would return AutomationException)
In the EJB code I have something like this.
try {
serverConn.connectToEISTier()
} catch (AutomatedException e) {
throw new MyApplicationException(Custom Message., ExceptionHelper.handleAutomatedException(e)); }
At the EJB level
we have create, and naming exceptions thrown either on failed lookup or something failing when creating the ejbs or there might be programming errors or there might be missing resources when EJB is trying to connect and possibly encounters data retrieval failures or Some sort of configuration error might be there in the deployment descriptor (user did soemthing wrong - wrong value for environment entry). All these are caught, and converted into runtime exception namely MyApplicationException. Where classification is deemed necessary we for e.g convert then contained exception to say configexception.
try {
lookup the context()
} catch(NamingException ex){
Cause = new myConfigException(lookup failed because .);
Throw new MyApplicationException(cause);
At the transport level: some communication exception happened.
At the client level:
Client might be calling the apis wrongly and breaching the contract, or possibly supplied wrong credentials.
Please share feedback / thoughts.

There is an interesting article that discusses EJB Exception Layering:
http://www-128.ibm.com/developerworks/java/library/j-ejbexcept.html
As a rule of thumb: in every layer, create two types of exceptions that extend from the appropriate class (application exceptions and system exceptions). The next layer catches these and handles them appropriately. This way, you hide the implementation of the layers. An example where this is implemented is Spring.
To summarize, I like your idea, but I define exceptions for every layer and not put them in one hiearchy.
Regards,
Lonneke

Defensive programming vs exception handling

Hi
im new to java programming and having problems getting my head around defensive programming vs exception handling.
i've read in my uni books about design by contract and the idea of defensive programming but im having problems with it.
so say i write the code.
String container = //some value
if (container.equals.("")) // so if i am looking for a value and find a empty String
   throw new // a custom exception i have made for this error.
else
   //do whatever i had planned with a non-empty String
}is this Defensive programming or exception handling. Or am i complete of base.
thanks

jverd wrote:
JustSomeGuy wrote:
Don't fall into the trap of saying "Meh, the exception will handle it". If you can forsee something easily being a problem, and it can be controlled, then control it. Save the exception handling for those things you don't forsee and those you can't control. I disagree. Or at least, I disagree with what I think you're saying.
For instance, if null is not a valid argument, then document it, and don't waste code defending against it. Either throw an explicit IllegalArgumentException, or let the NPE be thrown.
And absolutely under no circumstances should you ever write code that will deliberately lead to an exception, Eh? If an exceptional condition occurs, you should delibrately throw an exception. Consider if you will the following code snippet
import java.io.*;
class ExceptionExample {
    public static void main(String[] args)
        throws IOException {
        if (args.length == 0) {
            System.out.println("Must give filename as first arg.");
            return;
        FileInputStream in;
        try {
            in = new FileInputStream(args[0]);
        catch (FileNotFoundException e) {
            System.out.println("Can't find file: " + args[0]);
            return;
        int ch;
        while ((ch = in.read()) != -1) {
            System.out.print((char) ch);
        System.out.println();
        in.close();
} What I was saying in the first part is shown with the following part of the above code
if (args.length == 0) {
   System.out.println("Must give filename as first arg.");
   return;
} Would the exception handler that follows this peice of code have taken care of that? Sure! Would it be the best choice to just let the exception handler do it? No way no how!
It is easy to forsee someone forgetting or not realizing they need to add the filename as an arg and it can be controlled, so in this and most cases just like it the best choice is to either inform the user with a more specific statement than could be used in the exceptionhandler and do nothing or fix it yourself like for instance by using a default filename.
What I meant by deliberately throwing an exception can be illustrated with this small portion of my code above
int ch;
while ((ch = in.read()) != -1) {
    System.out.print((char) ch);
} A -1 to mark the EOF is expected and reaching the EOF is expected. There is absolutely nothing abnormal about this, so it should not be handled by an exception. But far to often I have seen novice and especially "think they know it all novices" use an exception in place of exactly this. They know the file will end, they know they must do something about that, but instead of doing it right they just set it up so an exception will be thrown and they can just handle it in the exceptionhandler. This is what I meant by deliberately throwing exceptions, in that an exception must be thrown in order for their program to work as intended. Bad, very bad.
Now that I have provided an example and further clarified my position do you still disagree? I can't imagine you would, so if you do I would be very interested in getting some further insight into your reasoning.
JSG

PL/SQL 101 : Exception Handling

Frequently I see questions and issues around the use of Exception/Error Handling in PL/SQL. More often than not the issue comes from the questioners misunderstanding about how PL/SQL is constructed and executed, so I thought I'd write a small article covering the key concepts to give a clear picture of how it all hangs together. (Note: the examples are just showing examples of the exception handling structure, and should not be taken as truly valid code for ways of handling things)
Exception Handling
Contents
1. Understanding Execution Blocks (part 1)
2. Execution of the Execution Block
3. Exceptions
4. Understanding Execution Blocks (part 2)
5. How to continue exection of statements after an exception
6. User defined exceptions
7. Line number of exception
8. Exceptions within code within the exception block
1. Understanding Execution Blocks (part 1)
The first thing that one needs to understand is almost taking us back to the basics of PL/SQL... how a PL/SQL execution block is constructed.
Essentially an execution block is made of 3 sections...
+---------------------------+
|    Declaration Section    |
+---------------------------+
|    Statements Section    |
+---------------------------+
|     Exception Section     |
+---------------------------+
The Declaration section is the part defined between the PROCEDURE/FUNCTION header or the DECLARE keyword (for anonymous blocks) and the BEGIN keyword. (Optional section)
The Statements section is where your code goes and lies between the BEGIN keyword and the EXCEPTION keyword (or END keyword if there is no EXCEPTION section). (Mandatory section)
The Exception section is where any exception handling goes and lies between the EXCEPTION keyword at the END keyword. (Optional section)
Example of an anonymous block...
DECLARE
.. declarative statements go here ..
BEGIN
.. code statements go here ..
EXCEPTION
.. exception handlers go here ..
END;
Example of a procedure/function block...
[CREATE OR REPLACE] (PROCEDURE|FUNCTION) <proc or fn name> [(<parameters>)] [RETURN <datatype>] (IS|AS)
.. declarative statements go here ..
BEGIN
.. code statements go here ..
EXCEPTION
.. exception handlers go here ..
END;
(Note: The same can also be done for packages, but let's keep it simple)
2. Execution of the Execution Block
This may seem a simple concept, but it's surprising how many people have issues showing they haven't grasped it. When an Execution block is entered, the declaration section is processed, creating a scope of variables, types , cursors, etc. to be visible to the execution block and then execution enters into the Statements section. Each statment in the statements section is executed in turn and when the execution completes the last statment the execution block is exited back to whatever called it.
3. Exceptions
Exceptions generally happen during the execution of statements in the Statements section. When an exception happens the execution of statements jumps immediately into the exception section. In this section we can specify what exceptions we wish to 'capture' or 'trap' and do one of the two following things...
(Note: The exception section still has access to all the declared items in the declaration section)
3.i) Handle the exception
We do this when we recognise what the exception is (most likely it's something we expect to happen) and we have a means of dealing with it so that our application can continue on.
Example...
(without the exception handler the exception is passed back to the calling code, in this case SQL*Plus)
SQL> ed
Wrote file afiedt.buf
1 declare
2    v_name VARCHAR2(20);
3 begin
4    select ename
5    into   v_name
6    from   emp
7    where empno = &empno;
8    dbms_output.put_line(v_name);
9* end;
SQL> /
Enter value for empno: 123
old   7:   where empno = &empno;
new   7:   where empno = 123;
declare
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at line 4
(with an exception handler, we capture the exception, handle it how we want to, and the calling code is happy that there is no error for it to report)
SQL> ed
Wrote file afiedt.buf
1 declare
2    v_name VARCHAR2(20);
3 begin
4    select ename
5    into   v_name
6    from   emp
7    where empno = &empno;
8    dbms_output.put_line(v_name);
9 exception
10    when no_data_found then
11      dbms_output.put_line('There is no employee with this employee number.');
12* end;
SQL> /
Enter value for empno: 123
old   7:   where empno = &empno;
new   7:   where empno = 123;
There is no employee with this employee number.
PL/SQL procedure successfully completed.
3.ii) Raise the exception
We do this when:-
a) we recognise the exception, handle it but still want to let the calling code know that it happened
b) we recognise the exception, wish to log it happened and then let the calling code deal with it
c) we don't recognise the exception and we want the calling code to deal with it
Example of b)
SQL> ed
Wrote file afiedt.buf
1 declare
2    v_name VARCHAR2(20);
3    v_empno NUMBER := &empno;
4 begin
5    select ename
6    into   v_name
7    from   emp
8    where empno = v_empno;
9    dbms_output.put_line(v_name);
10 EXCEPTION
11    WHEN no_data_found THEN
12      INSERT INTO sql_errors (txt)
13      VALUES ('Search for '||v_empno||' failed.');
14      COMMIT;
15      RAISE;
16* end;
SQL> /
Enter value for empno: 123
old   3:   v_empno NUMBER := &empno;
new   3:   v_empno NUMBER := 123;
declare
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at line 15
SQL> select * from sql_errors;
TXT
Search for 123 failed.
SQL>
Example of c)
SQL> ed
Wrote file afiedt.buf
1 declare
2    v_name VARCHAR2(20);
3    v_empno NUMBER := &empno;
4 begin
5    select ename
6    into   v_name
7    from   emp
8    where empno = v_empno;
9    dbms_output.put_line(v_name);
10 EXCEPTION
11    WHEN no_data_found THEN
12      INSERT INTO sql_errors (txt)
13      VALUES ('Search for '||v_empno||' failed.');
14      COMMIT;
15      RAISE;
16    WHEN others THEN
17      RAISE;
18* end;
SQL> /
Enter value for empno: 'ABC'
old   3:   v_empno NUMBER := &empno;
new   3:   v_empno NUMBER := 'ABC';
declare
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character to number conversion error
ORA-06512: at line 3
SQL> select * from sql_errors;
TXT
Search for 123 failed.
SQL>
As you can see from the sql_errors log table, no log was written so the WHEN others exception was the exception that raised the error to the calling code (SQL*Plus)
4. Understanding Execution Blocks (part 2)
Ok, so now we understand the very basics of an execution block and what happens when an exception happens. Let's take it a step further...
Execution blocks are not just a single simple block in most cases. Often, during our statements section we have a need to call some reusable code and we do that by calling a procedure or function. Effectively this nests the procedure or function's code as another execution block within the current statement section so, in terms of execution, we end up with something like...
+---------------------------------+
|    Declaration Section          |
+---------------------------------+
|    Statements Section          |
|            .                    |
| +---------------------------+ |
| |    Declaration Section    | |
| +---------------------------+ |
| |    Statements Section    | |
| +---------------------------+ |
| |     Exception Section     | |
| +---------------------------+ |
|            .                    |
+---------------------------------+
|     Exception Section           |
+---------------------------------+
Example... (Note: log_trace just writes some text to a table for tracing)
SQL> create or replace procedure a as
2    v_dummy NUMBER := log_trace('Procedure A''s Declaration Section');
3 begin
4    v_dummy := log_trace('Procedure A''s Statement Section');
5    v_dummy := 1/0; -- cause an exception
6 exception
7    when others then
8      v_dummy := log_trace('Procedure A''s Exception Section');
9      raise;
10 end;
11 /
Procedure created.
SQL> create or replace procedure b as
2    v_dummy NUMBER := log_trace('Procedure B''s Declaration Section');
3 begin
4    v_dummy := log_trace('Procedure B''s Statement Section');
5    a; -- HERE the execution passes to the declare/statement/exception sections of A
6 exception
7    when others then
8      v_dummy := log_trace('Procedure B''s Exception Section');
9      raise;
10 end;
11 /
Procedure created.
SQL> exec b;
BEGIN b; END;
ERROR at line 1:
ORA-01476: divisor is equal to zero
ORA-06512: at "SCOTT.B", line 9
ORA-06512: at line 1
SQL> select * from code_trace;
TXT
Procedure B's Declaration Section
Procedure B's Statement Section
Procedure A's Declaration Section
Procedure A's Statement Section
Procedure A's Exception Section
Procedure B's Exception Section
6 rows selected.
SQL>
Likewise, execution blocks can be nested deeper and deeper.
5. How to continue exection of statements after an exception
One of the common questions asked is how to return execution to the statement after the one that created the exception and continue on.
Well, firstly, you can only do this for statements you expect to raise an exception, such as when you want to check if there is no data found in a query.
If you consider what's been shown above you could put any statement you expect to cause an exception inside it's own procedure or function with it's own exception section to handle the exception without raising it back to the calling code. However, the nature of procedures and functions is really to provide a means of re-using code, so if it's a statement you only use once it seems a little silly to go creating individual procedures for these.
Instead, you nest execution blocks directly, to give the same result as shown in the diagram at the start of part 4 of this article.
SQL> ed
Wrote file afiedt.buf
1 create or replace procedure b (p_empno IN VARCHAR2) as
2    v_dummy NUMBER := log_trace('Procedure B''s Declaration Section');
3 begin
4    v_dummy := log_trace('Procedure B''s Statement Section');
5    -- Here we start another execution block nested in the first one...
6    declare
7      v_dummy NUMBER := log_trace('Nested Block Declaration Section');
8    begin
9      v_dummy := log_trace('Nested Block Statement Section');
10      select empno
11        into   v_dummy
12        from   emp
13       where empno = p_empno; -- Note: the parameters and variables from
                                     parent execution block are available to use!
14    exception
15      when no_data_found then
16        -- This is an exception we can handle so we don't raise it
17        v_dummy := log_trace('No employee was found');
18        v_dummy := log_trace('Nested Block Exception Section - Exception Handled');
19      when others then
20        -- Other exceptions we can't handle so we raise them
21        v_dummy := log_trace('Nested Block Exception Section - Exception Raised');
22        raise;
23    end;
24    -- ...Here endeth the nested execution block
25    -- As the nested block handled it's exception we come back to here...
26    v_dummy := log_trace('Procedure B''s Statement Section Continued');
27 exception
28    when others then
29      -- We'll only get to here if an unhandled exception was raised
30      -- either in the nested block or in procedure b's statement section
31      v_dummy := log_trace('Procedure B''s Exception Section');
32      raise;
33* end;
SQL> /
Procedure created.
SQL> exec b(123);
PL/SQL procedure successfully completed.
SQL> select * from code_trace;
TXT
Procedure B's Declaration Section
Procedure B's Statement Section
Nested Block Declaration Section
Nested Block Statement Section
No employee was found
Nested Block Exception Section - Exception Handled
Procedure B's Statement Section Continued
7 rows selected.
SQL> truncate table code_trace;
Table truncated.
SQL> exec b('ABC');
BEGIN b('ABC'); END;
ERROR at line 1:
ORA-01722: invalid number
ORA-06512: at "SCOTT.B", line 32
ORA-06512: at line 1
SQL> select * from code_trace;
TXT
Procedure B's Declaration Section
Procedure B's Statement Section
Nested Block Declaration Section
Nested Block Statement Section
Nested Block Exception Section - Exception Raised
Procedure B's Exception Section
6 rows selected.
SQL>
You can see from this that, very simply, the code that we expected may have an exception was able to either handle the exception and return to the outer execution block to continue execution, or if an unexpected exception occurred then it was able to be raised up to the outer exception section.
6. User defined exceptions
There are three sorts of 'User Defined' exceptions. There are logical situations (e.g. business logic) where, for example, certain criteria are not met to complete a task, and there are existing Oracle errors that you wish to give a name to in order to capture them in the exception section. The third is raising your own exception messages with our own exception numbers. Let's look at the first one...
Let's say I have tables which detail stock availablility and reorder levels...
SQL> select * from reorder_level;
   ITEM_ID STOCK_LEVEL
         1          20
         2          20
         3          10
         4           2
         5           2
SQL> select * from stock;
   ITEM_ID ITEM_DESC STOCK_LEVEL
         1 Pencils             10
         2 Pens                 2
         3 Notepads            25
         4 Stapler              5
         5 Hole Punch           3
SQL>
Now, our Business has told the administrative clerk to check stock levels and re-order anything that is below the re-order level, but not to hold stock of more than 4 times the re-order level for any particular item. As an IT department we've been asked to put together an application that will automatically produce the re-order documents upon the clerks request and, because our company is so tight-ar*ed about money, they don't want to waste any paper with incorrect printouts so we have to ensure the clerk can't order things they shouldn't.
SQL> ed
Wrote file afiedt.buf
1 create or replace procedure re_order(p_item_id NUMBER, p_quantity NUMBER) is
2    cursor cur_stock_reorder is
3      select s.stock_level
4            ,r.stock_level as reorder_level
5            ,(r.stock_level*4) as reorder_limit
6      from stock s join reorder_level r on (s.item_id = r.item_id)
7      where s.item_id = p_item_id;
8    --
9    v_stock cur_stock_reorder%ROWTYPE;
10 begin
11    OPEN cur_stock_reorder;
12    FETCH cur_stock_reorder INTO v_stock;
13    IF cur_stock_reorder%NOTFOUND THEN
14      RAISE no_data_found;
15    END IF;
16    CLOSE cur_stock_reorder;
17    --
18    IF v_stock.stock_level >= v_stock.reorder_level THEN
19      -- Stock is not low enough to warrant an order
20      DBMS_OUTPUT.PUT_LINE('Stock has not reached re-order level yet!');
21    ELSE
22      IF v_stock.stock_level + p_quantity > v_stock.reorder_limit THEN
23        -- Required amount is over-ordering
24        DBMS_OUTPUT.PUT_LINE('Quantity specified is too much. Max for this item: '
                                 ||to_char(v_stock.reorder_limit-v_stock.stock_level));
25      ELSE
26        DBMS_OUTPUT.PUT_LINE('Order OK. Printing Order...');
27        -- Here goes our code to print the order
28      END IF;
29    END IF;
30    --
31 exception
32    WHEN no_data_found THEN
33      CLOSE cur_stock_reorder;
34      DBMS_OUTPUT.PUT_LINE('Invalid Item ID.');
35* end;
SQL> /
Procedure created.
SQL> exec re_order(10,100);
Invalid Item ID.
PL/SQL procedure successfully completed.
SQL> exec re_order(3,40);
Stock has not reached re-order level yet!
PL/SQL procedure successfully completed.
SQL> exec re_order(1,100);
Quantity specified is too much. Max for this item: 70
PL/SQL procedure successfully completed.
SQL> exec re_order(2,50);
Order OK. Printing Order...
PL/SQL procedure successfully completed.
SQL>
Ok, so that code works, but it's a bit messy with all those nested IF statements. Is there a cleaner way perhaps? Wouldn't it be nice if we could set up our own exceptions...
SQL> ed
Wrote file afiedt.buf
1 create or replace procedure re_order(p_item_id NUMBER, p_quantity NUMBER) is
2    cursor cur_stock_reorder is
3      select s.stock_level
4            ,r.stock_level as reorder_level
5            ,(r.stock_level*4) as reorder_limit
6      from stock s join reorder_level r on (s.item_id = r.item_id)
7      where s.item_id = p_item_id;
8    --
9    v_stock cur_stock_reorder%ROWTYPE;
10    --
11    -- Let's declare our own exceptions for business logic...
12    exc_not_warranted EXCEPTION;
13    exc_too_much      EXCEPTION;
14 begin
15    OPEN cur_stock_reorder;
16    FETCH cur_stock_reorder INTO v_stock;
17    IF cur_stock_reorder%NOTFOUND THEN
18      RAISE no_data_found;
19    END IF;
20    CLOSE cur_stock_reorder;
21    --
22    IF v_stock.stock_level >= v_stock.reorder_level THEN
23      -- Stock is not low enough to warrant an order
24      RAISE exc_not_warranted;
25    END IF;
26    --
27    IF v_stock.stock_level + p_quantity > v_stock.reorder_limit THEN
28      -- Required amount is over-ordering
29      RAISE exc_too_much;
30    END IF;
31    --
32    DBMS_OUTPUT.PUT_LINE('Order OK. Printing Order...');
33    -- Here goes our code to print the order
34    --
35 exception
36    WHEN no_data_found THEN
37      CLOSE cur_stock_reorder;
38      DBMS_OUTPUT.PUT_LINE('Invalid Item ID.');
39    WHEN exc_not_warranted THEN
40      DBMS_OUTPUT.PUT_LINE('Stock has not reached re-order level yet!');
41    WHEN exc_too_much THEN
42      DBMS_OUTPUT.PUT_LINE('Quantity specified is too much. Max for this item: '
                              ||to_char(v_stock.reorder_limit-v_stock.stock_level));
43* end;
SQL> /
Procedure created.
SQL> exec re_order(10,100);
Invalid Item ID.
PL/SQL procedure successfully completed.
SQL> exec re_order(3,40);
Stock has not reached re-order level yet!
PL/SQL procedure successfully completed.
SQL> exec re_order(1,100);
Quantity specified is too much. Max for this item: 70
PL/SQL procedure successfully completed.
SQL> exec re_order(2,50);
Order OK. Printing Order...
PL/SQL procedure successfully completed.
SQL>
That's better. And now we don't have to use all those nested IF statements and worry about it accidently getting to code that will print the order out as, once one of our user defined exceptions is raised, execution goes from the Statements section into the Exception section and all handling of errors is done in one place.
Now for the second sort of user defined exception...
A new requirement has come in from the Finance department who want to have details shown on the order that show a re-order 'indicator' based on the formula ((maximum allowed stock - current stock)/re-order quantity), so this needs calculating and passing to the report...
SQL> ed
Wrote file afiedt.buf
1 create or replace procedure re_order(p_item_id NUMBER, p_quantity NUMBER) is
2    cursor cur_stock_reorder is
3      select s.stock_level
4            ,r.stock_level as reorder_level
5            ,(r.stock_level*4) as reorder_limit
6            ,(((r.stock_level*4)-s.stock_level)/p_quantity) as finance_factor
7      from stock s join reorder_level r on (s.item_id = r.item_id)
8      where s.item_id = p_item_id;
9    --
10    v_stock cur_stock_reorder%ROWTYPE;
11    --
12    -- Let's declare our own exceptions for business logic...
13    exc_not_warranted EXCEPTION;
14    exc_too_much      EXCEPTION;
15 begin
16    OPEN cur_stock_reorder;
17    FETCH cur_stock_reorder INTO v_stock;
18    IF cur_stock_reorder%NOTFOUND THEN
19      RAISE no_data_found;
20    END IF;
21    CLOSE cur_stock_reorder;
22    --
23    IF v_stock.stock_level >= v_stock.reorder_level THEN
24      -- Stock is not low enough to warrant an order
25      RAISE exc_not_warranted;
26    END IF;
27    --
28    IF v_stock.stock_level + p_quantity > v_stock.reorder_limit THEN
29      -- Required amount is over-ordering
30      RAISE exc_too_much;
31    END IF;
32    --
33    DBMS_OUTPUT.PUT_LINE('Order OK. Printing Order...');
34    -- Here goes our code to print the order, passing the finance_factor
35    --
36 exception
37    WHEN no_data_found THEN
38      CLOSE cur_stock_reorder;
39      DBMS_OUTPUT.PUT_LINE('Invalid Item ID.');
40    WHEN exc_not_warranted THEN
41      DBMS_OUTPUT.PUT_LINE('Stock has not reached re-order level yet!');
42    WHEN exc_too_much THEN
43      DBMS_OUTPUT.PUT_LINE('Quantity specified is too much. Max for this item: '
                              ||to_char(v_stock.reorder_limit-v_stock.stock_level));
44* end;
SQL> /
Procedure created.
SQL> exec re_order(2,40);
Order OK. Printing Order...
PL/SQL procedure successfully completed.
SQL> exec re_order(2,0);
BEGIN re_order(2,0); END;
ERROR at line 1:
ORA-01476: divisor is equal to zero
ORA-06512: at "SCOTT.RE_ORDER", line 17
ORA-06512: at line 1
SQL>
Hmm, there's a problem if the person specifies a re-order quantity of zero. It raises an unhandled exception.
Well, we could put a condition/check into our code to make sure the parameter is not zero, but again we would be wrapping our code in an IF statement and not dealing with the exception in the exception handler.
We could do as we did before and just include a simple IF statement to check the value and raise our own user defined exception but, in this instance the error is standard Oracle error (ORA-01476) so we should be able to capture it inside the exception handler anyway... however...
EXCEPTION
WHEN ORA-01476 THEN
... is not valid. What we need is to give this Oracle error a name.
This is done by declaring a user defined exception as we did before and then associating that name with the error number using the PRAGMA EXCEPTION_INIT statement in the declaration section.
SQL> ed
Wrote file afiedt.buf
1 create or replace procedure re_order(p_item_id NUMBER, p_quantity NUMBER) is
2    cursor cur_stock_reorder is
3      select s.stock_level
4            ,r.stock_level as reorder_level
5            ,(r.stock_level*4) as reorder_limit
6            ,(((r.stock_level*4)-s.stock_level)/p_quantity) as finance_factor
7      from stock s join reorder_level r on (s.item_id = r.item_id)
8      where s.item_id = p_item_id;
9    --
10    v_stock cur_stock_reorder%ROWTYPE;
11    --
12    -- Let's declare our own exceptions for business logic...
13    exc_not_warranted EXCEPTION;
14    exc_too_much      EXCEPTION;
15    --
16    exc_zero_quantity EXCEPTION;
17    PRAGMA EXCEPTION_INIT(exc_zero_quantity, -1476);
18 begin
19    OPEN cur_stock_reorder;
20    FETCH cur_stock_reorder INTO v_stock;
21    IF cur_stock_reorder%NOTFOUND THEN
22      RAISE no_data_found;
23    END IF;
24    CLOSE cur_stock_reorder;
25    --
26    IF v_stock.stock_level >= v_stock.reorder_level THEN
27      -- Stock is not low enough to warrant an order
28      RAISE exc_not_warranted;
29    END IF;
30    --
31    IF v_stock.stock_level + p_quantity > v_stock.reorder_limit THEN
32      -- Required amount is over-ordering
33      RAISE exc_too_much;
34    END IF;
35    --
36    DBMS_OUTPUT.PUT_LINE('Order OK. Printing Order...');
37    -- Here goes our code to print the order, passing the finance_factor
38    --
39 exception
40    WHEN exc_zero_quantity THEN
41      DBMS_OUTPUT.PUT_LINE('Quantity of 0 (zero) is invalid.');
42    WHEN no_data_found THEN
43      CLOSE cur_stock_reorder;
44      DBMS_OUTPUT.PUT_LINE('Invalid Item ID.');
45    WHEN exc_not_warranted THEN
46      DBMS_OUTPUT.PUT_LINE('Stock has not reached re-order level yet!');
47    WHEN exc_too_much THEN
48      DBMS_OUTPUT.PUT_LINE('Quantity specified is too much. Max for this item: '
                              ||to_char(v_stock.reorder_limit-v_stock.stock_level));
49* end;
SQL> /
Procedure created.
SQL> exec re_order(2,0);
Quantity of 0 (zero) is invalid.
PL/SQL procedure successfully completed.
SQL>
Lastly, let's look at raising our own exceptions with our own exception numbers...
SQL> ed
Wrote file afiedt.buf
1 create or replace procedure re_order(p_item_id NUMBER, p_quantity NUMBER) is
2    cursor cur_stock_reorder is
3      select s.stock_level
4            ,r.stock_level as reorder_level
5            ,(r.stock_level*4) as reorder_limit
6            ,(((r.stock_level*4)-s.stock_level)/p_quantity) as finance_factor
7      from stock s join reorder_level r on (s.item_id = r.item_id)
8      where s.item_id = p_item_id;
9    --
10    v_stock cur_stock_reorder%ROWTYPE;
11    --
12    exc_zero_quantity EXCEPTION;
13    PRAGMA EXCEPTION_INIT(exc_zero_quantity, -1476);
14 begin
15    OPEN cur_stock_reorder;
16    FETCH cur_stock_reorder INTO v_stock;
17    IF cur_stock_reorder%NOTFOUND THEN
18      RAISE no_data_found;
19    END IF;
20    CLOSE cur_stock_reorder;
21    --
22    IF v_stock.stock_level >= v_stock.reorder_level THEN
23      -- Stock is not low enough to warrant an order
24      [b]RAISE_APPLICATION_ERROR(-20000, 'Stock has not reached re-order level yet!');[/b]
25    END IF;
26    --
27    IF v_stock.stock_level + p_quantity > v_stock.reorder_limit THEN
28      -- Required amount is over-ordering
29

its nice article, have put up this one the blog
site,Nah, I don't have time to blog, but if one of the other Ace's/Experts wants to copy it to a blog with reference back to here (and all due credit given ;)) then that's fine by me.
I'd go for a book like "Selected articles by OTN members" or something. Does anybody have a list of links of all those mentioned articles?Just these ones I've bookmarked...
Introduction to regular expressions ... by CD
When your query takes too long ... by Rob van Wijk
How to pipeline a function with a dynamic number of columns? by ascheffer
PL/SQL 101 : Exception Handling by BluShadow

Exception handling is not working in GCC compile shared object

Hello,
I am facing very strange issue on Solaris x86_64 platform with C++ code compiled usging gcc.3.4.3.
I have compiled shared object that load into web server process space while initialization. Whenever any exception generate in code base, it is not being caught by exception handler. Even though exception handlers are there. Same code is working fine since long time but on Solaris x86, Sparc arch, Linux platform
With Dbx, I am getting following stack trace.
Stack trace is
dbx: internal error: reference through NULL pointer at line 973 in file symbol.cc
[1] 0x11335(0x1, 0x1, 0x474e5543432b2b00, 0x59cb60, 0xfffffd7fffdff2b0, 0x11335), at 0x11335
---- hidden frames, use 'where -h' to see them all ----
=>[4] __cxa_throw(obj = (nil), tinfo = (nil), dest = (nil), , line 75 in "eh_throw.cc"
[5] OBWebGate_Authent(r = 0xfffffd7fff3fb300), line 86 in "apache.cpp"
[6] ap_run_post_config(0x0, 0x0, 0x0, 0x0, 0x0, 0x0), at 0x444624
[7] main(0x0, 0x0, 0x0, 0x0, 0x0, 0x0), at 0x42c39a
I am using following link options.
Compile option is
/usr/sfw/bin/g++ -c -I/scratch/ashishas/view_storage/build/coreid1014/palantir/apache22/solaris-x86_64/include -m64 -fPIC -D_REENTRANT -Wall -g -o apache.o apache.cpp
Link option is
/usr/sfw/bin/g++ -shared -m64 -o apache.so apache.o -lsocket -lnsl -ldl -lpthread -lthread
At line 86, we are just throwing simple exception which have catch handlers in place. Also we do have catch(...) handler as well.
Surpursing things are..same issue didn't observe if we make it as executable.
Issue only comes if this is shared object loaded on webserver. If this is plain shared object, opened by anyother exe, it works fine.
Can someone help me out. This is completly blocking issue for us. Using Solaris Sun Studio compiler is no option as of now.

shared object that load into web server process space
... same issue didn't observe if we make it as executable.When you "inject" your shared object into some other process a well-being of your exception handling depends on that other process.
Mechanics of x64 stack traversing (unwind) performed when you throw the exception is quite complicated,
particularly involving a "nearly-standartized" Unwind interface (say, Unwind_RaiseException).
When we are talking about g++ on Solaris there are two implementations of unwind interface, one in libc and one in libgcc_s.so.
When you g++-compile the executable you get it directly linked with libgcc_s.so and Unwind stuff resolves into libgccs.
When g++-compiled shared object is loaded into non-g++-compiled executable's process _Unwind calls are most likely already resolved into Solaris libc.
Thats why you might see the difference.
Now, what exactly causes this difference can vary, I can only speculate.
All that would not be a problem if _Unwind interface was completely standartized and properly implemented.
However there are two issues currently:
* gcc (libstdc++ in particular) happens to use additional non-standard _Unwind calls which are not present in Solaris libc
naturally, implementation details of Unwind implementation in libc differs to that of libgccs, so when all the standard _Unwind
routines are resolved into Solaris version and one non-standard _Unwind routine is resolved into gcc version you get a problem
(most likely that is what happens with you)
* libc Unwind sometimes is unable to decipher the code generated by gcc.
However that is likely to happen with modern gcc (say, 4.4+) and not that likely with 3.4.3
Btw, you can check your call frame to see where _Unwind calls come from:
where -h -lIf you indeed stomped on "mixed _Unwind" problem then the only chance for you is to play with linker
so it binds Unwind stuff from your library directly into libgccs.
Not tried it myself though.
regards,
__Fedor.

Exception Handling in bounded taskflows - expected behaviour

Hi,
I'm currently reviewing exception handling in bounded task flows and some things does not seems to be very clear for me.
(q1) Does it make sense that a bounded task flow calls a method (via a method activity) defined on the page definition of another page (outside of the BTF) by using a #{data.xxxmyPageDef.myMethodName.execute} EL expression?
(q2) Is is correct to expect the application to execute the method marked as ExceptionHandler in the taskflow, whenever an exception occurs?
(q3) I created 5 different scenarios where I call a service method which throws an exception, from within a page fragment of the BTF.
(q3 – sc1) Call a service method through the binding layer of the current page (by using #{bindings.xxx.execute})
Result: A dialog containing the exception message appears.
This is what I expected. Althought, the exception handler method does not seems to be invoked.(q3 – sc2) Call a service method through a task flow method activity using #{bindings.xxx.execute}
Result: A dialog containing the exception message appears.
This is what I expected. Althought, the exception handler method does not seems to be invoked.(q3 – sc3) Call a service method through a task flow method activity using #{data.myPageFragementPagedef.xxx.execute} (accessing the pageDef of the page fragment)
Result: Nothing happens.
This is not what I expected. Although, the exception handler method does nog seems to be invoked, I expect the ADF Error Handler to create a FacesMessage.(q3 – sc4) Call a service method through a task flow method activity using #{data.myPageContainingThePageFragmentPageDef.xxx.execute} (accessing the page containing the BTF region)
Result: Nothing happens.
This is not what I expected. Although, the exception handler method does nog seems to be invoked, I expect the ADF Error Handler to create a FacesMessage. (q3 – sc5) Call a service method through a task flow method activity using #{data.aPageOutsideTheBTFPageDef.xxx.execute} (accessing a page outside the BTW)
Result: Nothing happens.
This is not what I expected. Although, the exception handler method does nog seems to be invoked, I expect the ADF Error Handler to create a FacesMessage. (q4) How can it be possible that – without an exception handler – exceptions occur when calling method activities, without the exceptions being translated to FacesMessages?
Thanks in advance,
Koen Verhulst
JDeveloper 11.1.1.4

Koen,
+(q1) Does it make sense that a bounded task flow calls a method (via a method activity) defined on the page definition of another page (outside of the BTF) by using a #{data.xxxmyPageDef.myMethodName.execute} EL expression?+
No. Exceptions should be handled locally.
+(q2) Is is correct to expect the application to execute the method marked as ExceptionHandler in the taskflow, whenever an exception occurs?+
Only for exceptions that are before Render Response. The Render Response Phase is not handled in ADFc. So exceptions that occur in managed beans may fall through
+(q3) I created 5 different scenarios where I call a service method which throws an exception, from within a page fragment of the BTF.+
+(q3 – sc1) Call a service method through the binding layer of the current page (by using #{bindings.xxx.execute}) Result: A dialog containing the exception message appears.+
This is what I expected. Althought, the exception handler method does not seems to be invoked.
The binding layer has an error handler you can override in the DataBinings.cpx file
+(q3 – sc2) Call a service method through a task flow method activity using #{bindings.xxx.execute}+
Result: A dialog containing the exception message appears.
This is what I expected. Althought, the exception handler method does not seems to be invoked.
Again, you use the binding layer to invoke the service
+(q3 – sc3) Call a service method through a task flow method activity using #{data.myPageFragementPagedef.xxx.execute} (accessing the pageDef of the page fragment)+
Result: Nothing happens.
This is not what I expected. Although, the exception handler method does nog seems to be invoked, I expect the ADF Error Handler to create a FacesMessage.
Never use such a call. Its bad practice as there is no guarantee the container you reference is active. Always have the method call activity have its own binding defined when accessing a method call activity. I know there are lots of example floating aroundthat you #{data ...} and many are from 10.1.3. This should be avoided alltogether though
+(q3 – sc4) Call a service method through a task flow method activity using #{data.myPageContainingThePageFragmentPageDef.xxx.execute} (accessing the page containing the BTF region)+
Result: Nothing happens.
This is not what I expected. Although, the exception handler method does not seems to be invoked, I expect the ADF Error Handler to create a FacesMessage.
Again, this is not a proper use of the ADF framework.
+(q3 – sc5) Call a service method through a task flow method activity using #{data.aPageOutsideTheBTFPageDef.xxx.execute} (accessing a page outside the BTW)+
Result: Nothing happens. This is not what I expected. Although, the exception handler method does nog seems to be invoked, I expect the ADF Error Handler to create a FacesMessage.
accessing a page outside the BTW (!!!) This should ring a worst practices alarm on your laptop (obviously doesn't do it either)
+(q4) How can it be possible that – without an exception handler – exceptions occur when calling method activities, without the exceptions being translated to FacesMessages?+
Exceptions are not handled in a single place but stacked. The business service raises an exception and passes it to the binding layer if not handled. The binding layer handles the exception and if it can't passes it to ADFc. ADFc can handle this exception if it is not during Render Response.
Bottom line: There is no single point of exception handling. So as a recommendation for best practices
- Catch and handle exceptions as close as possible to their origins
- If things can go wrong, thy will - use try/catch blocks in managed beans
- Use an exception handling activity in all bounded task flows. In the case of task flow call activities being used exceptions can bubble up to the caller. However, this would take users out of their current application context
- Exceptions not handled in ADFc can be intercepted by overriding the application task flow exception handler (used by the exception handler activities). This would give you a chance e.g. to handle issues during Render Response
- Never fight the framework, never bend the framework: Don't use out of scope access to page definitions and resources. Exception handling is not a replacement for bad code practices (sorry for saying this, its not meant to be rude) :-)
Though I don't have a qualified numbers of bugs open for exception handling in ADF between 11.1.1.4 and now (and some that are open), but there are issues reported in this area. If there is something that really feels wrong, please go ahead and file a bug and provide a test case for development to have a look. The Render Response issue, for example is something we are aware of and that is in discussion (afaik knows, there is a change in exception handling in JSF 2 that may have an impact to what we can do in ADFc).
thanks
Frank

Exception handling-Design issue -Very interesting

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