Các thư viện mẫu tạo điều kiện cho sự phát triển của các ứng dụng Ajax với các lớp học , và , và làm giảm mã JavaScript với các chức năng tiện ích. Trong chương này, chúng tôi đã thêm các chức năng của nguyên mẫu và các lớp học để ứng dụng web Ajax mà chúng tôi phát triển trong các chương trước để giảm bớt các mã JavaScript trong các ứng dụng web. | Updating a DOM Element with 59 Fig. Updating ValidationMessage Div If a Catalog Id field value is specified that is not valid the validationMessage div message gets updated to indicate that the Catalog Id value is not valid as shown in Fig. . Fig. Non Valid Catalog Id 60 3 Less JavaScript with Prototype Summary The prototype library facilitates the development of Ajax applications with and classes and reduces JavaScript code with utility functions. In this chapter we added prototype functions and classes to the Ajax web application that we developed in the previous chapter to reduce the JavaScript code in the web application. 4 Ajax with Java-GWT Introduction Google Web Toolkit GWT is a Java framework for developing Ajax applications. Ajax being a JavaScript based web technique GWT generates the required JavaScript and HTML from the Java classes. GWT provides a library of dynamic reusable user interface UI components for UI applications. Only a front-end Java class is required to be specified to create a GWT application. GWT applications may be run with commonly used browsers such as IE and Netscape and Safari. Installing GWT First we need to download GWT . Extract the zip file to a directory. Install a recent version of JDK if not already installed. We shall be using JDK . GWT does not require any installer application. All the required files are available in the directory in which the zip file is extracted. GWT provides the command-line tool applicationcreator to generate a GWT application. GWT also provides a projectcreator tool to generate an Eclipse project for the GWT application but we shall only discuss the command-line GWT application. A GWT application may be run in two modes hosted mode and web mode. In hosted mode a GWT application is run as Java bytecode in the JVM. In web mode the GWT application is run as JavaScript and HTML created with Java-to-JavaScript
