As the integration between Windows OS, Servers & Tools is getting better and they are leveraging the powerful .NET platform, the number of projects for Java to .NET migration has increased considerably. The Productivity improvements introduced by MOSS & Composite applications and VSTS for both end users and development teams has triggered the motivation of moving to .NET further.
In this post I will cover two important aspects of Java to .NET migration projects :
- How different Java/J2ee technology stack maps to .NET technology stack ?
- Various migration options and paths available to migrate with least impact on production sites and efforts.
Java/J2SE/J2EE to .NET Technology Stack Mapping
WEB LAYER
| Swing | Windows Forms |
| AWT | Windows Forms |
| JSPs | ASPX pages |
| JSTL | ASP.NET Server controls |
| Http Filters | HttpModule |
| Servlets | HttpHandlers |
| Web Container/Application Server | ASP.NET / IIS |
| Applets | Windows Form User Controls |
APP LAYER
| EJBs | Enterprise Services, Remoting, WCF |
| RMI /IIOP | Enterprise Services, Remoting, WCF |
| EJB Container | Enterprise Services, IIS, WAS |
| Session EJB | Enterprise Services, Remoting, WCF |
| Entity EJB - CMP | No equivalent |
| Entity EJB - BMP | Serviced components with DataSets |
Database / Integration Layer
| JDBC | ADO.NET : Connected : Data readers Disconnected : DataSets |
| JMS | MSMQ, System.Messaging, WCF |
| JCA | Biztalk |
Runtime, Language & Others Components
| jdk | .NET BCL |
| JRE | CLR |
| Packaged as .jar | Assembly( dll,exe, module) |
| JAXB | XML Serialization, XSD Tool |
| JAXP | System.XML |
| Development tools | Visual Studio Team System - complete ALM |
| Documentation | SandCastle |
MIGRATION PATHS
Currently three options are available for migrating java aps to .net :
- Tool : Java Language Conversion Assistant (JLCA) - This tool is from Microsoft and currently is in Version 3.0. It takes java source code files and converts them to CSharp files. It also creates projects and support classes wherever direct mapping between jdk and BCL is not available. While over the period it has improved a lot but still its not 100% and some manual modifications will be required after conversion.
- Visual J#.NET : Its an another managed language from Microsoft which has syntax very similar to Java and provide libraries with functionality similar to jdk 1.1.4. Recommended if you plan to continue using existing java development skills but not recommended for interoperability with other managed applications.
- jbimp : This tool comes with J# installation and can be used to convert byte code in .class files directly to MSIl assemblies. Its a good option for simple class files and uses J# libraries internally.
All the above tools assist in moving java apps to .net but there are limitations with each of them. If you plan to automate this process, you may have to write some custom tools to fill the gaps.
If you plan for a staged migration, java to .net interoperability options can also be used like web services, remoting bridges, etc. so that whole of app need not be converted at one go.
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