Exceptions in a loop

Question

I have a quartz job which calls my status service to update the status multiple items in a loop.
Like I have 5 items whose status I want to update with the job.
the job iterates collection of items and calls update item , now for some reason a item update fails capture the exception caused by update failure and continue with next item and and finally throw all the exceptions related in update failure ,all the way it is how to handle exceptions ina loop ?

Answer 1

Hi Miro,
You can only throw one exception, and the caller should know what kind of exception to expect.
You could create your own exception class, perhaps something like this:
public class PsuedoDemandException extends Exception{
  public PseudoDemandException(String message, Exception cause){
    super(message, cause);
    causes.add(cause);
  public void addCause(Exception cause){
    causes.add(cause);
  public ArrayList<Exception> getCauses(){
    return causes;
  private ArrayList<Exception> causes = new ArrayList<Exception>();
}Now, put a try... catch in each iteration of your loop. If and when the first exception is thrown, you will instantiate your PseudoDemandException with a message and that exception; if further exceptions are thrown, you will add them to your PseudoDemandException.
Once you have finished with the loop, check to see if your PseudoDemandException is null and, if not, then throw it. The caller only has to look out for one kind of exception, which will contain details of any exceptions thrown during processing:
public void updatePseudoDemandStatus() throws PseudoDemandException{
  List storageRequests=getStorageRequestService().findOPPseDmReq();
  //Set your exception to null to begin with...
  PseudoDemandException demandException = null;
  for(Iterator i=storageRequests.iterator();i.hasNext();){
    StorageRequest storageRequest=(StorageRequest)i.next();
    //For each iteration, try the updatePseudoDemandStatus(storageRequest)...
    try{
      updatePseudoDemandStatus(storageRequest);
    //... and, if an exception is thrown...
    catch(Exception e){
      //... then either create a PseudoDemandException (if it is null)...
      if(demandException == null)
        demandException = new PseudoDemandException("Oops, didn't work!", e);
      //...or add this exception to it (if it isn't null, which infers that this is not the first exception to be thrown)
      else
        demandException .addCause(e);
  if(demandException != null)
    throw demandException;  // No need to thrown a new exception; you already have one to throw!
}The caller can then call the method and check for the PseudoDemandException:
try{
  updatePseudoDemandStatus();
catch(PseudoDemandException pde){
  for(Exception cause : pde.getCauses())
    System.out.println(cause);
}This will achieve what you want, but check that you really do need such a high level of information before you go ahead and use it -- if there's a SQLException, for example, does it not perhaps indicate a problem that could render the whole method's operation invalid? If so, then perhaps the exception should be thrown there and then and the rest of the loop foregone. I'm not saying this is what you should do, just suggesting that you double-check what you need to achieve.
All the best,
Chris.