Migration from J2EE to .NET

Overview
Hi all, here are some quick tips to get you started, in case you need to migrate a J2EE based application to a .NET based application.

We approach the migration tier wise. Firstly, a technology mapping between both the platforms :--

Service or Feature	.NET	J2EE
GUI	WinForms	SWING & AWT
Web GUI	ASP.NET	JSP
Web Scripting	ISAPI, HttpHandler, HttpModule	Servlet, Filter
Server Side Business Logic Component	Serviced Component (COM+)	EJB Session Beans
Server side Data component	Serviced Component (COM+) with DB Logic	EJB BMP Entity Beans
Server Side Data Component	Object Spaces	EJB CMP Entity Beans
Naming	ADSI	JNDI
Remote Invocation	.NET Remoting	RMI or RMI-IIOP
Data Access	ADO.NET	JDBC
Messaging	MSMQ	JMS
Transactions	COM+ or MTS	JTA

Highlights of the migration strategy

Presentation Tier JSP -> ASP.NET
Business Logic Tier EJB -> COM+ (.NET Enterprise Service)
Data Access Tier JDO/JDBC -> ADO.NET

i. Presentation tier migration

JSP -> ASP .NET (sample code snippets)

JSP scriptlet :--

<!--Scriptlet--> 

<%
	for(int i = 0; i < 3; i++) {
		out.println(i + "<br>"); 
	}
%>

ASP .NET scriptlet :--

<!--Scriptlet-->
<%
	for(int i = 0; i < 3; i++) {
		Response.Write(i + "<br>");
	}
%>

JSP expression :--

<%= new java.math.BigDecimal(10.1).negate() %>

ASP .NET expression :--

<%= System.Decimal.Negate(new System.Decimal(10.1)) %>

JSP declaration :--

<%!
	public String foo() {
		return "foo";
	}
%>

ASP .NET declaration :--

<script runat="server" language="c#">
	public virtual string foo() 
	{
		return "foo";
	} 
</script>

Implicit objects :--

JSP ASP .NET

application Application

session Session

request Request

response Response

out Response.Write

Cookies :--

Creating a cookie and setting its expiry time.

Code in J2EE :--

<%
	Cookie userCookie = new Cookie("user", "uid123");
	userCookie.setMaxAge(60*60*24*365); // 1 year
	response.addCookie(userCookie);
%>

Code in .NET :--

<%
	System.Web.HttpCookie userCookie = 
		new System.Web.HttpCookie("user", "uid123");
	System.DateTime dateTime = System.DateTime.Now;
	System.TimeSpan timeSpan =
		new System.TimeSpan(0, 0, 60*60*24*365); // 1 year
	
	cookie.Expires = dateTime.Add(timeSpan);
	Response.Cookies.Add(userCookie); 
%>

Beans :--

Java code :--

public class Bean1 {

	private String text = "Hello";
	
	public Bean1 () {}
	
	public String getText() {
		return this.text;
	}
	
	public String setText(String text) {
		this.text = text;
	}
}

C# code :--

using System; 

public class Bean1{

	private string text = "Hello";
	
	public Bean1() {} 

	public string Text
	{
		get { return text; }
		set { text = value; }
	}
}

Converting Servlets to ASP .NET code behind :--

Servlet sample code :--

import javax.servlet.*; 
import javax.servlet.http.*;

import java.io.*;

public class SimpleServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, 
			HttpServletResponse response)
			throws ServletException, java.io.IOException {
		
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		
		out.println("<html><body>");
		out.println("Simple Servlet Body");
		out.println("</body></html>");
		
		out.close();
	}
}

ASP .NET code-behind sample :--

using System; 
using System.Web; 
using System.Web.UI; 

public class SimpleServlet : System.Web.UI.Page
{
	private void Page_Load(object sender, EventArgs args)
	{
		Response.ContentType = "text/html";
		
		Response.Write("<html><body>");
		Response.Write("Simple Servlet Body");
		Response.Write("</body></html>");
	}
}

Tag Library :--

JSP	ASP .NET
Tag Handler Class JSP Tag Library Descriptor JSP Tag Library Directive	ASP.NET Web User Controls ASP.NET Web Custom Control

JSP tag lib Sample code :--

<!� JSP --> 
<!� the source file is specified in the TLD --> 

<%@ taglib uri="taglib.tld" prefix="tags" %> 

<tags:sample />

ASP .NET tag lib Sample code :--

<!� ASP.NET --> 

<%@ Register TagPrefix="tags" TagName="sample"
	Src="ExampleTag.ascx" %> 

<tags:sample id="mySample" runat="server" />

Converting Java Applets to .NET Winforms control :--

Applet code :--

package helloWorldPackage; 

public class HelloWorld extends Applet {

	public void paint(Graphics g) {
		g.drawString(getParameter("parameter1"), 25, 25);
	}
	
	public void init() {}
	public void start() {}
	public void stop() {}
}

.NET Winforms code :--

namespace HelloWorldPackage
{
	public class HelloWorld : System.Windows.Forms.UserControl
	{
		string parameter1;
		bool isActive;
		
		public HelloWorld()
		{
			init();
		}
		
	protected override void OnPaint(PaintEventArgs e)
	{
		e.Graphics.DrawString(parameter1, Font,
			new SolidBrush(ForeColor), 25, 25);
	}
	
	public void init()
	{
		this.GotFocus +=
			new EventHandler(this.helloWorldControl1_Start);
		this.LostFocus +=
			new EventHandler(this.helloWorldControl1_Stop);
	}
}