Proper way to handle Runtime Exceptions in Java

Question

I'm completely new to this code and begun to questions the design choices of the original developers.

I have a multi-threaded Java application that processes a number of tasks. My job is to fix the exception handling in the code so that when a RuntimeException occurs (iBatis and/or NullPointerException) the rest of the tasks are executed instead of the thread terminating. I want to know what is the best way to deal with the exception handling below:

public  List<WorkUnit> performModule(List<WorkUnit> listOfInputs)
            throws ModuleException {

        List<WorkUnit> listOfOutputs = new ArrayList<WorkUnit>();
        for (WorkUnit mi : listOfInputs) {
            WorkUnit mo=null;
            try {
                if (mi instanceof BulkOrder) {
                    mo = performModuleOperation(...);
                } else if (mi instanceof Order) {
                    mo = performModuleOperation(...);
                } else if (mi instanceof PreReleaseLoad) { 
                    mo = performModuleOperation(...);
                } else if (mi instanceof Load) {
                    mo = performModuleOperation(...);
                }
                listOfOutputs.add(mo);
            } catch (OMSException e) {
                  if (e.shouldProcessFurther()) {
                      listOfOutputs.add((mo!=null) ? mo : mi);
                  } 
                 //save error to database - code was removed
                  if ( e.getExceptionType().equals(ExceptionType.TECHNICAL)) {
                        if ( e instanceof ModuleException ) {
                            throw (ModuleException) e;
                        } else {
                        throw new ModuleException(e);   
                        }
                  } 
            } catch (Throwable th) {
                ModuleException me = new ModuleException(th);
                ExceptionHandler.logException(me, (WorkUnit)mi,orderDelegate);
                throw me;
            }

        }
        return listOfOutputs ;
    }

I have two major problems. 1) The catch for the Throwable object. I understand that they want to capture checked exceptions and unchecked exceptions. I guess that they want to check for Errors as well but the Sun documentation for exception handling specifically states that this is highly advised against. In the event you get a really serious error like the JVM running out of memory you may not be able to recover. This could be caught in a log file and I don't agree with it needing to be dealt with. Personally if you are tracking technical and applications exceptions errors doesn't seem like something that you would monitoring like any other exception. I could be wrong...

2) It isn't clear how the exceptions are being handled. In the code below the, which the exception throws to the code above it wraps a regular exception be it checked or unchecked into a custom exception and throws that. The code above looks for an OMSException which is the parent of every custom exception in the entire application. Is this a good design? You can see where they include a ExceptionType to the custom exception object. There already seems to be an functionality built into the existing exception handling of Java. If it is an application exception then throw a custom exception. If it is a technical exception, something is null when it isn't suppose to be or a database connection problem, then catch a unchecked exception from Java and react accordingly. This whole thing seems confusing. I just want to know what thoughts other have on the whole thing.

public Order performModuleOperation(Order order)
            throws ModuleException {                                

        try {   
            Map<String, Rule> rules = ...                       

         }      
        catch (InductException ie) {
            throw ie;
        }
        catch (Exception e) {       
            e.printStackTrace();
            throw new InductException(e.toString(),e);
        }
        return order;
    }

Answer 1

There are two ways to deal with a thread that exits with an unchecked exception. The first option is to run the thread from with in a try-catch block that catches all errors and exceptions:

Thread t = new MyThread();
try {
  lauchThreadHere(t);
} catch (Throwable e) {
  // log `e` or re-launch thread `t` or do something else.
}

Another way is to implement Thread.UncaughtExceptionHandler:

public class MyUeh implements Thread.UncaughtExceptionHandler {
    public void uncaughtException(Thread t, Throwable e) {
         // log `e` or re-launch thread `t` or do something else.
    }
}

Thread t = new MyThread();
t.setUncaughtExceptionHandler(new MyUeh());
lauchThreadHere(t);