JavaCompute node exception handling

Exceptions can occur during message flow processing (during the evaluate() method) and during the onInitialize() method. If you implemented the onInitialize() method, and you detect an unrecoverable error in the node configuration, an exception of class MbException is issued and the flow fails to initialize. Either your flow fails to deploy, and error message BIP4157 is issued, or the flow does not start and does not appear in the list of running flows.

Do not run code in an onInitialize() method that depends on another external resource that might not be there because the broker will not retry calls to that method. If you need to initialize an external connection, for example, initialize it during the first call to the evaluate() method. If the initialization does not work, you can throw an exception that will be handled like any other flow exception.

The following example code shows a simple implementation of a JavaCompute node that routes a CSV message to the out or alt terminals, based on a header field that contains a positive or negative number. If the text in the field is not numeric, a NumberFormatException is thrown. The example code shows how this exception can be caught and thrown as a MbUserException so that the handling of MbException built into IBM Integration Bus from JavaCompute nodes can be used.

public void evaluate(MbMessageAssembly assembly) throws MbException {
  MbOutputTerminal out = getOutputTerminal("out");
  MbOutputTerminal alt = getOutputTerminal("alternate");
  
  MbMessage message = assembly.getMessage();
  int routeTo = 0;
  try {
    // ----------------------------------------------------------
    // Add user code below
    String routingValue = (String)message.evaluateXPath("string(/csv/header/route_to)");
    routeTo = Integer.parseInt(routingValue);
    
    
    // End of user code
    // ----------------------------------------------------------
  } catch (java.lang.NumberFormatException e ) {
    // Example Exception handling
    MbUserException mbue = new MbUserException(this, "evaluate()", "","", e.toString(), null);
    throw mbue;
  }
  
  // The following should only be changed
  // if not propagating message to the 'out' terminal
  if ( routeTo > 0 )
    out.propagate(assembly);
  else
    alt.propagate(assembly);
}