Embedding a Web Application in Eclipse and Tomcat

Christopher L Merrill
Private Message cm68669 on EclipseZone
©2006 Web Performance, Inc
January 30, 2006
v1.0

Introduction

Both Eclipse and it's RCP brethren have a webserver embedded within them: a re-packaged Apache Tomcat server. It is included as a part of the Eclipse help system. Is it possible to deploy a web-application to that embedded server and make it available to the application and/or an external browser?   (hint: yes)

First, you might ask: Why would you want to do this? After all, if I'm building a rich-client application using the Eclipse RCP, then why would I want to deploy a web application and access it through the browser? The point of the building the application as a rich client was to get away from web apps, right? I've heard a number of reasons why one would want to do this. Our motiviation was simple: reporting. Our application performs a number of detailed analyses and generates reports summarizing the results. We could certainly present this information in a rich-client GUI. The problem occurs when the users demand output to pass on to other parts of their business, either electronically or in print. If we implemented the reports with a GUI, we would need to duplicate the effort to get the reports into a paper or electronic format. Instead, we can use a web-based reporting tool and generate the reports in HTML, accessible via an embedded browser within the application. Then the report can be easily output in HTML for sending electronically or exported to PDF or other formats, depending on the choice of reporting tools.

This article assumes that the reader already knows how to write, package and deploy Eclipse plug-ins and JEE web applications.

It should be noted that this example uses internal, undocumented Eclipse 3.1 APIs.  There is no guarantee it will work in future Eclipse releases. Hopefully, the Eclipse team has recognized the value of these APIs to developers and will make them public and supported.

The Goal

1. Deploy a web application in Eclipse's embedded Tomcat server
2. Allow that web application to pull data from an Eclipse plug-in and display it in an embedded browser in an Eclipse view or editor

The Plan

This plug-in works in a somewhat circular fashion: A user action in our plug-in causes an embedded browser to be pushed to a URL that corresponds to a servlet in our embedded web-app. The servlet then queries the plug-in for the data to display and formats it as a web page. The page is then returned back to the embedded browser where it is displayed in our plug-in.

Here is a picture of our working plug-in:



In the plug-in shown above, the view consists of a text field where the user has entered some text. After pushing the browse button, the resulting web page is displayed in the embedded browser.

How To Do It?

1. register our web application
2. start the Tomcat instance
3. find where the Tomcat instance is running to determine what URL will access our Servlet
4. when the browse button in the view is pushed, send the browser to this URL
   
5. access our plug-in from within the servlet to get access to the input entered in the view
   

Register the web application

<web-app>
    <servlet>
        <servlet-name>PluggedIn</servlet-name>
        <servlet-class>example.webapp.PluggedInServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>PluggedIn</servlet-name>
        <url-pattern>/pluggedin/*</url-pattern>
    </servlet-mapping>
</web-app>

The only additional step is to register an extension with an Eclipse extension point in our plug-ins descriptor file (plugin.xml).

<extension
    point="org.eclipse.help.base.webapp">
    <webapp
        default="true">
    </webapp>
</extension>

Start the Tomcat instance

WebappManager.start(context, plugin_id, path);

1. context path for the web application - all paths mapped in your web application will be relative to this
2. ID of the plugin owning the web application - this allows the WebappManager to find the application files
3. path of the web application folder, relative to the plugin folder

public static boolean ensureWebappRunning()
    {
    if (!_started)
        {
        WebappManager.start("example", "example.webapp.plugin", Path.EMPTY);
        _started = true;
        }
    }

Find where the Tomcat instance is running

WebappManager.getPort();

    public String getExampleServletURL(String servlet_path)
        {
        return "http://" + WebappManager.getHost() + ":" + 
            WebappManager.getPort() + "/example/" + servlet_path;
        }

Send the browser to the URL

    public void widgetSelected(SelectionEvent e)
        {
        ExampleWebappPlugin.ensureWebappRunning();
        String url = ExampleWebappPlugin.getInstance().getExampleServletURL(servlet_path);
        _browser.setUrl(url);
        }

Get input from the view into the servlet

out.println("<p>");
out.println("You typed: " + ExampleWebappPlugin.getInstance().getTextEntry());
out.println("</p>");

Downloads & Feedback

If you would like to discuss this report, please post your questions at the EclipseZone page for this article. Or you can send me a private message (username cm68669) at EclipseZone

Version History

v1.0 - 1st public release (30 jan 06)

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