Servlets and XML: Made for Each Other

If you're using Oracle 8i instead of DB2, you'll find that it boasts similar functions (see Resources). For databases that aren't XML-aware, you could store the XML document as a character large object (CLOB) and retrieve the document as a chunk of text.

However your database is set up, you need to do three things to get this code to work:

1. First, change the DbOwner, DbUserid, and DbPasswd variables to the correct values for your system.
   

   /////////////////////////////////////////////////////////////////////////////// // Be sure to change these three strings appropriately, or the // // servlet won't work. // /////////////////////////////////////////////////////////////////////////////// DbUserid = "xxxxxxxx"; DbPasswd = "xxxxxxxx"; DbOwner = "xxxxxxxx";

   
   
   

2. Next, use the JDBC driver that works with your system. We're using DB2.

   staticStringJDBCDriver = "COM.ibm.db2.jdbc.app.DB2Driver"; ... try { Class.forName("COM.ibm.db2.jdbc.app.DB2Driver").newInstance(); } catch (Exceptione) { System.out.println("Can't get the driver!"); e.printStackTrace(); }

   
   
   

3. If you want to, change the SQL query. To keep the demo simple, we're simply retrieving all of the XML documents from the order column in the sales_order_view table.

   // We hardcoded the SQL statement here; this would be more // sophisticated if we qualified the query based on user input. Stringquery = "select order from " + DbOwner + ".sales_order_view";

   
   
   

In the service method, our servlet connects to DB2, executes a query (the results of which are a set of XML documents), parses the query results, and writes the parsed data to the output stream. Listing 6 shows the most relevant sections of the code:

// We hardcoded the SQL statement here; this would be more

// sophisticated if we qualified the query based on user input.

Stringquery = "select order from " + DbOwner + ".sales_order_view";



    res.setContentType("text/xml");



    try

      {

        ConInfoindex = newConInfo();

        Connectioncon = getCon(index);

        Statementstmt = con.createStatement();

        ResultSetrs = stmt.executeQuery(query);



        ...



        // Display the result set.  We take the XML doc from each row,

// parse it, then print the DOM tree.  rs.next() returns

// false when there are no more rows.

while (rs.next())

          { 

            StringnextOrder = rs.getString(1).trim();

            Documentdoc = null;

            StringReadersr = newStringReader(nextOrder);

            InputSourceiSrc = newInputSource(sr);

            

            try

              {

                parser.parse(iSrc);

                doc = parser.getDocument();

              }

            catch (Exceptione)

              {

                System.err.println("Sorry, an error occurred: " + e);

              }

            

            if (doc != null)

              printDOMTree(doc, out);

          }

To see all the details, check out the HTML view of the complete listing or view the Java source file directly.

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