DWR-Direct web remoting
a Java open source library that helps developers write web sites that include Ajax technology. // 用ajax 寫網站
It allows code in a web browser to use Java functions running on a web server as if those functions were within the browser. //用 web server 上 java 的功能
It consists of two main parts:
whereas in reality the Java code runs in the web server and has full access to web server resources.
For security reasons the web developer must configure exactly which Java classes are safe to export (which is often called web.xml or dwr.xml).
DWR does not consider the web browser / web server protocol to be important, and prefers to ensure that the programmer’s interface is natural.
The greatest challenge to this is to marry the asynchronous nature of Ajax with the synchronous nature of normal Java method calls.
In the asynchronous model, result data is only available some time after the initial call is made. DWR solves this problem by allowing the web developer to specify a function to be called when the data is returned using an extra method parameter. This extra method is called CallBack Method. The value returned from the java function will be passed to the callback method.
Dojo tool kit: