Tutorials : Handling Messages, Errors and Exceptions in Struts 1.1 :

Using ActionMessages

The ActionMessages class resembles the List class we used above in that it is a container for the messages. The messages themselves are held in instances of the ActionMessage class:

Here's a piece of code from an Action class that uses these classes:

Listing 3: Using ActionMessages

ActionMessages messages = new ActionMessages();
ActionMessage msg = new ActionMessage("data.ok");
messages.add("message1", msg);

msg = new ActionMessage("data.continue");
messages.add("message2", msg);

saveMessages(request, messages);

As you can see there are some differences when you compare this to Listing 1:

1. You don't give the message text directly to ActionMessage. Instead you give a key to the Struts message resource file (also called "the application property file"). I've specified these two lines in this file:

       data.ok=Data saved successfully data.continue=Please
       continue
       

   It's considered good practice to keep your fixed texts in the message resource file, and it also gives you the possibility to support several languages in your application. 
2. You give a "label" when you add an ActionMessage. This makes it possible to look up the message and stick it in your HTML wherever you like it. We'll see below how to do this.
   It's possible to have more than one message with a given label.
   If the message is not related to anything special you use the label ActionErrors.GLOBAL_ERROR.

To show all the messages in the browser you add these lines to your jsp-page (note the resemblance with the code from listing 2):

Listing 4: The messages tag in use

<html:messages id="msg" message="true">
<bean:write name="msg"/><br>
</html:messages>

This will give you exactly the same output as above:

As you can see the <html:messages> tag loops over all the messages in the ActionMessages class. If you want to pick a single message from the class you specify its label as the property:

<html:messages id="msg2" message="true" property="message1">
<bean:write name="msg2"/><br>
</html:messages>

This makes it possible to place messages, for example, next to input fields in a form.

One more thing about the ActionMessage class: you may specify parameters to the message taken from the message resource file:

msg = new ActionMessage("data.do", "stop");
messages.add("message2", msg);

With "data.do=Please {0}" this will display as "Please stop".

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