We have created a custom exception at the ADF-BC level by overriding the JboException class. In order to use application-specific error codes, we have introduced two new constructors. Both of them accept the error code as a parameter. One of them also accepts the message error parameters.

public ExtJboException(final String errorCode, final Object[] errorParameters) {
super(ResourceBundle.class, errorCode, errorParameters);
}

In our constructor, we call the base class' constructor and pass the message error code and parameters to it.

Then we override the getMessage() method in order to construct the exception message. In getMessage(), we first get access to the error messages resource bundle by calling ResourceBundle.getBundle() as shown in the following code snippet:

final ResourceBundle messagesBundle = ResourceBundle.getBundle(ERRORS_BUNDLE, Locale.getDefault());

This method accepts the name of the resource bundle and the locale. For the name of the resource bundle, we pass the constant ERRORS_BUNDLE, which we define as com.packt.jdeveloper.cookbook.shared.bc.exceptions.messages.ErrorMessages. This is the ErrorMessages.properties file in the com/packt/jdeveloper/cookbook/shared/bc/exceptions/messages directory where we have added all of our messages. For the locale, we use the default locale by calling Locale.getDefault().

Then we proceed by loading the error message from the bundle:

errorMessage = this.getErrorCode() + " - " + messagesBundle.getString(MESSAGE_PREFIX + this.getErrorCode());

An error message definition in the messages resource bundle looks similar to the following:

message.00001=This is an error message that accepts two parameters. The first parameter is '{1}'. The second parameter is '{2}'.

As you can see, we have added the string prefix message. to the actual error message code. How you form the error message identifiers in the resource bundle is up to you. You could, for example, use a module identifier for each message and change the code in getMessage() appropriately. Also, we have used braces, that is, {1}, {2} as placeholders for the actual message parameter values. Based on all these, we constructed the message identifier by adding the message prefix to the message error code as: MESSAGE_PREFIX + this.getErrorCode() and called getString() on the messagesBundle to load it.

Then we proceed with iterating the message parameters. In a similar fashion, we call getString() on the parameters bundle to load the parameter values.

The parameter definitions in the parameters resource bundle look similar to the following:

parameter.FirstParameter=Hello
parameter.SecondParameter=World

So we add the prefix parameter to the actual parameter identifier before loading it from the bundle.

The last step is to replace the parameter placeholders in the error message with the actual parameter values. We do this by calling replaceAll() on the raw error message, as shown in the following code snippet:

errorMessage = errorMessage.replaceAll("\\{" + (i + 1) + "}", parameterValue);

For testing purposes, we have added a main() method to test our custom exception. You will similarly throw the exception in your business components code, as follows:

throw new ExtJboException("00001", // message code new String[] { "FirstParameter", "SecondParameter" } // message parameters);

You can combine the error message and the error message parameters bundles into a single resource bundle, if you want, and change the getMessage() method as needed to load both from the same resource bundle.

public String getMessage() {
return BundleUtils.loadMessage(this.getErrorCode(), this.getErrorParameters());
}