This servlet uses the JDataConnect type 3 driver to query an SQL database running on a different host from the machine where the servlet is running.
The components in this three-tier example are shown in the figure, below.
Three- tier architecture. Shows applet communicating with WWW sever and servlet. Applet forms separate connection with servlet, which contacts ODBC registry for particular database running on a different machine, loads driver, and interacts with remote dbms through the driver using SQL. Data packaged by servlet and returned to applet.
Servlet
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
public class jbsJDCServlet extends HttpServlet {
//***** Servlet access to data base
//***** through JDataConnect type 3 driver, on servlet host
//***** connecting to SQL server, on different host
public void doGet (HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String url = "jdbc:JDataConnect://jbspc-cs.cs.unc.edu/jbsPlantsSQL";
String query = "SELECT * FROM PlantsSQL.dbo.plants";
try {
Class.forName ("JData1_2.sql.$Driver");
Connection con = DriverManager.getConnection ( url, "", "" );
Statement stmt = con.createStatement ();
ResultSet rs = stmt.executeQuery (query);
printResultSet ( resp, rs );
rs.close();
stmt.close();
con.close();
} // end try
catch (SQLException ex) {
while (ex != null) { /*
System.out.println ("SQL Exception: " + ex.getMessage ());
ex = ex.getNextException (); */
} // end while
} // end catch SQLException
catch (java.lang.Exception ex)
{ ; }
} // end doGet
private void printResultSet ( HttpServletResponse resp, ResultSet rs )
throws SQLException {
ServletOutputStream out;
try {
resp.setContentType("text/html");
out = resp.getOutputStream();
out.println("<html>");
out.println("<head><title>jbsJDCServlet</title></head>");
out.println("<body>");
out.println("<center><font color=AA0000>");
out.println("<h3>jbs JDataConnect Servlet</h3>");
out.println("<h3>Data Retrieved:</h3>");
out.println("<table border='1'>");
int numCols = rs.getMetaData().getColumnCount ();
while ( rs.next() ) {
out.println("<tr>");
for (int i=1; i<=numCols; i++) {
out.print("<td>" + rs.getString(i) + "</td>" );
} // end for
out.println("</tr>");
} // end while
out.println("</table>");
out.println("</font></center>");
out.println("</body>");
out.println("</html>");
out.close();
} // end try
catch ( IOException except) {
} // end catch
} // end returnHTML
} // end jbsJDCServlet