3. Building View Components
3.1 Overview
This chapter focuses on the task of building the View components for use with the Struts framework. Many applications rely on JavaServer Pages (jsp) technology to create the presentation layer. The Struts distribution includes a comprehensive JSP tag library that provides support for building internationalized applications, as well as for interacting with input forms. Several other topics related to the View components are briefly discussed.
3.2 Internationalized Messages
A few years ago, application developers could count on having to support only residents of their own country, who are used to only one (or sometimes two) languages, and one way to represent numeric quantities like dates, numbers, and monetary values. However, the eXPlosion of application development based on web technologies, as well as the deployment of sUCh applications on the Internet and other broadly Accessible networks, have rendered national boundaries invisible in many cases. This has translated (if you will pardon the pun) into a need for applications to support internationalization (often called "i18n" because 18 is the number of letters in between the "i" and the "n") and localization.
Struts builds upon the standard classes available on the Java platform to build internationalized and localized applications. The key concepts to become familiar with are:
Locale - The fundamental Java class that supports internationalization is Locale. Each Locale represents a particular choice of country and language (plus an optional language variant), and also a set of formatting assumptions for things like numbers and dates.
ResourceBundle - The java.util.ResourceBundle class provides the fundamental tools for supporting messages in multiple languages. See the Javadocs for the ResourceBundle class, and the information on Internationalization in the documentation bundle for your JDK release, for more information.
PropertyResourceBundle - One of the standard implementations of ResourceBundle allows you to define resources using the same "name=value" syntax used to initialize properties files. This is very convenient for preparing resource bundles with messages that are used in a web application, because these messages are generally text oriented.
MessageFormat - The java.text.MessageFormat class allows you to replace portions of a message string (in this case, one retrieved from a resource bundle) with arguments specified at run time. This is useful in cases where you are creating a sentence, but the Words would appear in a different order in different languages. The placeholder string {0} in the message is replaced by the first runtime argument, {1} is replaced by the second argument, and so on.
MessageResources - The Struts class org.apache.struts.util.MessageResources lets you treat a set of resource bundles like a database, and allows you to request a particular message string for a particular Locale (normally one associated with the current user) instead of for the default Locale the server itself is running in.
