IBM BPM, V8.0.1, All platforms > Programming IBM BPM > Service Component Architecture programming > SCA programming model fundamentals > Invocation styles

Exception handling for asynchronous invocation

When a service component is invoked asynchronously, the client and service provider are run in different threads, and error conditions can occur in either thread. The client may experience a system exception during the invocation, or the service provider may experience a business or system exception while servicing the request.

In IBM BPM, there is always an asynchronous counterpart of the synchronous interface.

Here is an example of an asynchronous interface:

public interface StockQuoteAsync {
public Ticket getQuoteAsync(String arg0);
public Ticket getQuoteAsyncWithCallback(String arg0);
public float getQuoteResponse(Ticket ticket, long timeout) throws InvalidSymbolException;}

Here is the client code for a call using the invocation pattern for deferred response:

Ticket ticket = stockQuote.getQuoteAsync(symbol);
try {
	quote = stockQuote.getQuoteResponse(ticket, Service.WAIT);
	} catch (InvalidSymbolException s) {
	System.out.println(This is business exception declared in the interface.);
	} catch (ServiceRuntimeException e) {
	System.out.println("Unchecked system exception detected");}

Like a synchronous invocation, InvalidSymbolException indicates that the request has reached the service provider, which has thrown a business exception stating that the symbol is invalid. This business exception is the only one declared by the interface. exceptions like InvalidSymbolException are caught only with clients using a reference.

In addition to the business exception declared, the client can receive system exceptions such as connection error that happens while sending the message. The client cannot receive system exceptions that happen in the service thread (the thread on the service side of the asynchronous invocation). According to the SCA asynchronous programming model, runtime exceptions that occur at the target component are not returned to the source component.

Exception case on asynchronous exception handling

There is one exception to the SCA asynchronous programming model rule that runtime exceptions that occur at the target component are not returned to the source component. If the source component is a Business Process component or Staff Process, system exceptions that occur in the target service component are returned to the caller. This capability lets business process designers model and catch system exceptions, and run error logic if a BPEL client returns a system exception.

Invocation styles