86 4 Ajax with Java-GWT
Fig. 4.21 Creating a Catalog Entry
If the Catalog ID value for which a new catalog entry is created is
specified in the Catalog ID field again, the validation message indicates
that the Catalog ID is not valid as shown in Fig. 4.22.
Fig. 4.22 A Catalog Id becomes Non Valid after a Catalog Entry is created
4.6 Summary 87
4.6 Summary
The Google Web Toolkit is an Ajax framework for Java and also provides
a set of user interface components (widgets). A JRE emulation library is
also included in GWT. A limitation of GWT is that by default only the
Java classes in the JRE emulation library may be used in a GWT
application. For example, if a JDBC connection with a database is to be
created in a GWT application using the java.sql library, the Java-to-
JavaScript compiler does not compile the Java class and generates an error.
5 Ajax with Java-DWR
5.1 Introduction
Direct Web Remoting (DWR) is a Java open source library for developing
Ajax applications. DWR consists of two components: JavaScript running
in the browser that sends requests and dynamically updates the web page
with the response, and a Servlet running on the server that processes
requests and sends response back to the browser. Remoting in DWR
implies that Java class methods are remoted as JavaScript functions in the
browser. DWR dynamically generates JavaScript corresponding to Java
classes and the JavaScript may be run in the browser just as any other
JavaScript class library.
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