sexta-feira, agosto 10, 2012

DWR: The first project

DWR – Direct Web Remoting


DWR is a framework used to work with Ajax call on Java implementation. An Ajax call is an asynchronous request of the system resource, in other words, while the request is processed, the user can interact with other resource of the system until the response of the first request.


Is part of the Ajax call: HTML, XHTML, CSS, DOM XML, XMLHttpRequest, JavaScript. The great benefit of the Ajax utilization, certainly, is the possibility of providing better interaction of use with the application, build rich applications for web and finally there’s a better response time. 
In order to optimize the development of Java Applications using Ajax, the use of DWR is a good choice, because it is an OpenSource tool, it provides security calls to Java codes by integrable browser with the features of the main frameworks market. It encapsulates details and complexity of the implementation of XMLHttpRequest, and performs Java class conversion for a JavaScript implementation, this way, allowing the use of a browser.

The diagram below shows the DWR use in an Ajax request to Java implementation.
   

 
THE PROJECT

Using the Eclipse IDE, create a new Dynamic Web Project, as shown on the picture below.

 
To obtain the dwr.jar file, do the download that in: http://directwebremoting.org/dwr/downloads/index.html;
The DWR use the artifact commons-logging.jar, so, this file is necessary and can be obtained from: http://commons.apache.org/logging/
Copy the two files into the WEB-INF\lib of your project.
We must set the DWR servlet in our project, open the file web.xml of your project and add:


  DWR Servlet
  dwr-invoker  
  org.directwebremoting.servlet.DwrServlet
  
     debug
true dwr-invoker /dwr/*


It’s also necessary the creation of a file as shown below, this should be included on the WEB-INF directory of your project with the name dwr.xml.

  
    
          
  


After these settings have been done, the DWR should be ready to use. Start your server, in this tutorial was used the Tomcat7, and access your application as the following one:

 

Note that the Project lists the JavaScript to JDate, it contains the java.util.Date class in a JavaScript version, in other words, this class was converted to JavaScript.
This project shows the IMC calculus, in this case, the call for this method and the response presentation will be by Ajax. For this, create a new class as the following picture:
 

We implement the logic as:
package br.com.serjava.dwr;

public class CalculoIMCAjax {

 public String calcularImc(Double peso, Double altura) {

  Double imc = (peso / Math.pow(altura, 2));

  if (imc < 18.5) {
   return "Seu imc é: " + imc + " Abaixo de 18,5 Você está abaixo do peso ideal";
  } else if (imc >= 18.5 && imc < 24.9) {
   return "Seu imc é: " + imc + " Entre 18,5 e 24,9 Parabéns — você está em seu peso normal!";
  } else if (imc >= 24.9 && imc < 29.9) {
   return "Seu imc é: " + imc + " Entre 25,0 e 29,9 Você está acima de seu peso (sobrepeso)";
  } else if (imc >= 29.9 && imc < 34.9) {
   return "Seu imc é: " + imc + " Entre 30,0 e 34,9 Obesidade grau I";
  } else if (imc >= 34.9 && imc <= 39.9) {
   return "Seu imc é: " + imc + " Entre 35,0 e 39,9 Obesidade grau II";
  } else {
   return "40,0 e acima Obesidade grau III";
  }

 }
 
}


The next step will be the mapping of the class above as a DWR object, for this, you must edit the file dwr.xml and insert:

       


The last stage we are going to create the page that will show the content, creat, if it doesn’t exist, the page index.jsp into the WebContent directory, following the implementation below: 
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>




Insert title here
   
     
   
 
 






Altura (m)
Peso (kg)

The expected result will be:

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Um comentário:

  1. very nice post! I could finally understand what Ajax is! :-) Even though I am no longer programming, I really thought your incations very useful! :)

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