The RSS Reader project uses the Visual Studio Web Site format, which was the default project format in Visual Studio 2005 (sans SP1). For Grasshopper to work with the project, first convert the Website into the Web Application project type:

1. In Visual Studio, create a new “RSSReader” project from the Visual C# for Java EE > ASP.NET AJAX-enabled Web application template. Grasshopper adds two new project types to Visual Studio’s New Project dialog: Visual C# for Java EE and Visual Basic for Java EE.
2. Open the RSS Reader Web site in the same solution.
3. Drag-and-drop all project files (except for the references) from the Website to the RSSReader project, overwriting any default items.
4. Right-click the RSSReader project node in the Solution Explorer and select Convert to Web Application.

The RSS Reader uses version 1.0.0.1 of the ASP.NET RSS Toolkit. Since the download package from CodePlex does not include any Visual Studio project file, create a new .NET class library project (“RSSToolkit”) from the source code and add it to the solution. To build RSS Toolkit, you also need to add references to System.Configuration, System.Design, System.Drawing, System.Web and System.Windows.Forms to the class library project. Verify that the build succeeds and then generate a Grasshopper project from RSS Toolkit.

Grasshopper adds a new context menu item to Solution Explorer’s project nodes: Generate Java EE Project. Choosing this option for the RSSToolkit project brings up a wizard that analyzes project dependencies and suggests alternatives for unresolved references. In this case, because the RSS Toolkit doesn’t have any non-framework dependencies, the wizard does not present any options. When finished, a new project is created in your solution: RSSToolkit.JavaEE.

Now, add a reference from RSSReader to the Java-version of RSSToolkit by selecting Add Java Reference... (another new menu item added by Grasshopper, see Figure 1) and select RSSToolkit.JavaEE from the Project tab.

Remove the .NET versions of the Web site and the RSS Toolkit project from the solution because they are no longer required.

Building for Java
If you try to build the newly generated Java projects, you’ll see errors referring to classes and methods that are “not supported.” Due to the fundamental differences between the .NET and Java platforms, there are some limitations in the Java runtime libraries used to implement the .NET Framework. These limitations are responsible for the build errors above, and they are caught when Grasshopper validates the .NET code.

To build the application successfully, modify the source code to use only supported methods and classes. When targeting the Java platform, the full Java Framework is callable from Visual C# or Visual Basic code, so you always have the choice of either using supported .NET classes and methods, or using the Java Framework. If you’re looking to maintain a single source code base for targeting both platforms, use the conditional compilation directives (#if JAVA) to separate sections that are unique to .NET or Java.

In the sample application, the errors you see are due to the usage of BuildProvider, which is unsupported due to its tight coupling to System.CodeDom. Inspect the RSS Toolkit classes that are generating errors and see that they are only needed for generating RSS feeds, and not for consuming them – which is the only requirement in the RSS Reader. The pragmatic solution here is to ignore the three classes that are responsible for generating RSS when building for Java. There are two ways to accomplish this, and the choice between them is more a matter of style than anything else. You can either exclude the files from the RSSToolkit.JavaEE project, or wrap them with a preprocessor directive:

#if !JAVA
// .NET specific code goes here
#endif

You also need to wrap the code accessing these classes with the #if !JAVA directive.

Another issue to keep in mind when moving from the .NET platform to Java is that you need to use the correct case for file names, because .NET and Windows don’t distinguish between lowercase or uppercase, while Java does.

Using ASP.NET AJAX in Grasshopper
The RSS Reader also depends on the AJAX Control Toolkit, a joint project between Microsoft and the developer community. Grasshopper provides full support for the AJAX Control Toolkit (as well as the Anthem.NET AJAX Toolkit), and comes bundled with the ported source code. To reference the AJAX Control Toolkit, open the project (by default available at C:\Program Files\Mainsoft for Java EE\Samples\CS\Tomcat\AjaxControlToolkit\), build it with Grasshopper, and add the output AjaxControlToolkit.jar file to your project’s references with the Add Java Reference... option. Make sure the assembly file (AjaxControlToolkit.dll) resides in the same folder as the .jar file.

The original RSS Reader project used a preview release of ASP.NET AJAX, and as such contains the tagMapping element in Web.config for enabling the AJAX validators. These types were removed from the official release of ASP.NET AJAX. To correct the problem, simply remove the tagMapping element from Web.config.

This time, the build succeeds. Start the Grasshopper bundled Tomcat server from Start > All Programs > Mainsoft for Java EE > Start Tomcat and run the application from Visual Studio with Ctrl-F5. Voilà! Tomcat runs the Java application, which was ported from ASP.NET.

Of course, this conversion is a one-time process. Now, you can continue to develop the source code in Visual C# or Visual Basic inside Visual Studio, as you would any .NET application, taking advantage of Visual Studio’s visual designer, debugger, IntelliSense, and other development features.

Adding new AJAX functionality to the RSS Reader for Java is virtually the same process as adding AJAX controls to an ASP.NET application deployed on Windows. As an example, use the AnimationExtender to blur the feed list when the mouse cursor isn’t hovering over it.

For the AJAX AnimationExtender control to be able to access the feed list, wrap it with an ASP.NET control; <asp:panel> serves this purpose well. Drag-and-drop the AnimationExtender control to the Default.aspx page’s design surface in Visual Studio and set its TargetControlID property to the ID of the <asp:Panel>. Now, define the animations for fading the list in and out on specific events:

<ajaxT:AnimationExtender ID=”AnimationExtender1”
runat=”server” TargetControlID=”FeedList”>
<Animations>
<OnLoad>
<FadeOut MinimumOpacity=”.2” />
</OnLoad>
<OnHoverOver>
<FadeIn MinimumOpacity=”.2” Duration=”.3” />
</OnHoverOver>
<OnHoverOut>
<FadeOut MinimumOpacity=”.2” />
</OnHoverOut>
</Animations>
</ajaxT:AnimationExtender>

While you’re at it, also replace the “(read more)” link to the full article text with an Ajaxy HoverMenu. Drag-and-drop the HoverMenuExtender control, also found in the AJAX Control Toolkit, to the DataList’s Item Template. Then, drop a HyperLink control there and databind the NavigateUrl property to the item’s link value:

<asp:HyperLink ID=”Popup” runat=”server”
BackColor=Beige BorderColor=DarkKhaki
Text=”View Original Item” NavigateUrl=’<%#
Eval(“link”)%>’/>
<ajaxT:HoverMenuExtender TargetControlID=”panelHeader” runat=”server”
PopupControlID=”Popup” PopupPosition=Right OffsetX=15 />

Finally, build and run the application to see that the changes work.

Deploying on Linux
So far, you have deployed the Java build target on the Grasshopper-bundled Tomcat Web application server, running locally on Windows. Now, let’s fulfill our promise to run this Web application on Linux. This is a straightforward process. First, build the Release_Java configuration of RSSReader to create a deployment-friendly WAR file.

The release configuration’s default setting enables Full Deployment Package (WAR) (a Grasshopper-specific project property) and tells the build system to generate a Web Archive (WAR) file, a compressed archive with all needed resources (HTML, JAR, images files, etc.).

Then, upload the WAR file to Tomcat on Linux via Tomcat Manager’s Web administration interface. The WAR file created in the previous step is located inside the local Tomcat’s installation directory, by default at C:\Program Files\Mainsoft for Java EE\jakarta-tomcat\webapps\.

Figure 2 shows the ASP.NET AJAX application hosted on Linux/Apache Tomcat.

Summary
This article shows you how to use ASP.NET AJAX to build applications for Linux, which is a very practical tool for multi-platform deployments. But we’re only scraping the surface of Grasshopper’s full potential to enable.NET–Java interoperability here. Unleash your creativity and use the power of Visual Studio development and the ASP.NET Framework to deploy Web applications to open source Web application servers!