Java servlets and XForms

This example shows one way to obtain and manipulate submitted XForms instance data within a Java Servlet. Our Servlet is called EchoPersonDataServlet, which takes the submitted XML and outputs to the browser in a tabular format the names and values of the XML elements. Any empty elments are ignored. (The full PHP code is available here.)

NOTE: If you wish to compile and use the EchoPerson Servlet with Tomcat you will need to have added the following .jar files to your classpath. %TOMCAT_HOME%\common\lib\servlet-api.jar, %TOMCAT_HOME%\common\endorsed\xercesImpl.jar and %TOMCAT_HOME%\common\endorsed\xmlParserAPIs.jar. You will also have to configure the web.xml file in your web application to reference the Servlet.

In the Servlet, to get hold of the XML instance data, we read in the body of the request to a string:

     ...    
     String xml      = new String("");
     String thisLine = new String("");
     ...
     BufferedReader br = request.getReader();
     while ((thisLine = br.readLine()) != null) {
          xml = xml.concat(thisLine);
     }
     ...              

Now we have the instance data in a string we will use DocumentBuilderFactory and DocumentBuilder objects along with the Document interface to help manipulate it. From java.sun.com - "The Document interface represents the entire HTML or XML document. Conceptually, it is the root of the document tree, and provides the primary access to the document's data".

     ...
     DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
     try {
          DocumentBuilder builder  = factory.newDocumentBuilder();
          Document        document = builder.parse(new InputSource(new StringReader(xml)));
     ...

All the rest of the Servlet does is to iterate through the nodes of the XML and format the names and values of the elements in an HTML table which is returned to the browser to be displayed.

NOTE: How to manipulate the submitted XForms data and whether to use DOM or SAX to do it is really up to the developer and it depends what the exact needs are. For more information on using XML and Java please take a look at the Java Web Services Tutorial.

To try this example for yourself:
NOTE: Installing and configuring Tomcat goes beyond the scope of this tutorial but listed below are the major steps involved in running this tutorial. For complete instructions on using web applications with Tomcat please follow the documentation available on the Apache website.

1. Install and configure Jakarta Tomcat 5 (download from The Apache Site).
2. Make sure that your CLASSPATH contains references to the servlet-api.jar, xercesImpl.jar and xmlParserAPIs.jar files that are mentioned earlier in this section.
3. Create your own 'webapp' structure and extract the person.html file to the root of it.
4. Extract the EchoPersonDataServlet.java file to the 'classes' directory of your webapp and compile.
5. Use the web.xml file for your webapp to map the EchoPersonDataServlet class to a URL.
6. Open the person.html file in notepad, or other text editor, and change the submission element action attribute to the value of the URL you specified in the web.xml file. Remember Tomcat defaults to use port 8080.
7. Start Tomcat, open Internet Explorer and point it to the location of the person.html file.
8. Change any data and submit the form.