mule

The Message class is a wrapper for an error message, its error code and other information. The messages are read from ResourceBundles usually from classpath.

The class MessageFactory encapsulates the lookup of ResourceBundles and creation of messages. Since each mule module should provide its own messages, subclasses of MessageFactory should be created. It is convention to put the module specific class in a subpackage called i18n.

Subclassing MessageFactory

package org.mule.module.foo.i18n;

public class FooMessages extends MessageFactory
{
    private static final String BUNDLE_PATH = getBundlePath("foo");
    
    public static final Message foo()
    {
        return createMessage(BUNDLE_PATH, 1);
    }
    
    public static final Message bar(String arg)
    {
        return createMessage(BUNDLE_PATH, 2, arg);
    }
    
    .
    .
    .
}

• Message instances are created using meaningful java methods, i.e. client code is less cluttered with message cration details.
• The method signature ensures that the right number of arguments is passed in to format the message.
• No more constants for message codes needed as there is exactly one occurrence of the constant in the code.
• By using the right MessageFactory subclass it is ensured that the correct ResourceBundle will be chosen for lookup.
• Formatting the input to messages can be taken out of the client code by putting it in this class