Direct Web Remoting, or DWR, is a

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...

library that helps developers write web sites that include

Ajax Ajax may refer to: Greek mythology and tragedy * Ajax the Great, a Greek mythological hero, son of King Telamon and Periboea * Ajax the Lesser, a Greek mythological hero, son of Oileus, the king of Locris * Ajax (play), ''Ajax'' (play), by the an ...

technology. It allows code in a

web browser A web browser, often shortened to browser, is an application for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's scr ...

to use Java functions running on a

web server A web server is computer software and underlying Computer hardware, hardware that accepts requests via Hypertext Transfer Protocol, HTTP (the network protocol created to distribute web content) or its secure variant HTTPS. A user agent, co ...

as if those functions were within the browser. The DWR project was started by Joe Walker in 2004, 1.0 released at August 29, 2005.

Application

*Code to allow

JavaScript JavaScript (), often abbreviated as JS, is a programming language and core technology of the World Wide Web, alongside HTML and CSS. Ninety-nine percent of websites use JavaScript on the client side for webpage behavior. Web browsers have ...

to retrieve data from a

servlet A Jakarta Servlet, formerly Java Servlet is a Java software component that extends the capabilities of a server. Although servlets can respond to many types of requests, they most commonly implement web containers for hosting web applicat ...

-based web server using Ajax principles. *A

JavaScript library A JavaScript library is a library of pre-written JavaScript code that allows for easier development of JavaScript-based applications, especially for AJAX and other web-centric technologies. They can be included in a website by embedding it directl ...

that makes it easier for the website developer to dynamically update the web page with the retrieved data. DWR takes a novel approach to Ajax by dynamically generating JavaScript code based on Java classes. Thus the web developer can use Java code from JavaScript as if it were local to the web browser; 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''). This method of remoting functions from Java to JavaScript gives DWR users a feel much like conventional

RPC RPC may refer to: Science and technology * Rational polynomial coefficient * Reactive Plastic Curtain, a carbon-dioxide-absorbing device used in some rebreather breathing sets * Regional Playback Control, a regional lockout technology for DVDs ...

mechanisms like RMI or

SOAP Soap is a salt (chemistry), salt of a fatty acid (sometimes other carboxylic acids) used for cleaning and lubricating products as well as other applications. In a domestic setting, soaps, specifically "toilet soaps", are surfactants usually u ...

, with the benefit that it runs over the web without requiring web browser plug-ins. 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. Here is a sample Callback: MJavaClassOnJs.getListProducts(selectedCategory, ) The callback is that function inside the

JSON JSON (JavaScript Object Notation, pronounced or ) is an open standard file format and electronic data interchange, data interchange format that uses Human-readable medium and data, human-readable text to store and transmit data objects consi ...

object passed as an additional parameter to the remoted function. With version 2.0, DWR supports Comet (also called "Reverse Ajax) where Java code running on the server can deliberately send dedicated JavaScript to a browser.

References

Bibliography

External links

*{{Official website Ajax (programming) JavaScript XML software Software using the Apache license Web frameworks 2005 software Free software programmed in Java (programming language)