Servlets, JDBC, and Inter-Servlet Communications - Developing Java Servlets - page 121

Now that you have created and understand the ConnectionPoolServlet , you can put it to use
with another example. This example is based on your TitleListServlet , except that you will
do a generic query with no request parameters. There are two important changes to this servlet.
The first is how it gets a connection and the second is how it releases that connection.

The TitleListGlobalPooledServlet gets a Connection object by calling the
ServletContext.getAttribute() method, passing it the key “CONNECTION_POOL” , which
returns a reference to the ConnectionPool object. It can then call the
ConnectionPool.getConnection() method to get a JDBC connection:

7

// Get a reference to the ConnectionPool from the Global
// ServletContext
pool =(ConnectionPool)
getServletContext().getAttribute(“CONNECTION_POOL”);

// Get a connection from the ConnectionPool
con = pool.getConnection();

When the servlet finishes with the connection, it must release it. This is done by calling the
ConnectionPool 's releaseConnection() method:

// Release the connection
pool.releaseConnection(con);

That is all there is to it. After you are finished with the ConnectionPool , it still resides in the
ServletContext waiting on future requests. You'll find the entire source for the
TitleListGlobalPooledServlet in Listing 7.11.

L ISTING 7.11 TitleListGlobalPooledServlet.java

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import java.sql.*;

import ConnectionPool.*;

public class TitleListGlobalPooledServlet extends HttpServlet {

public void init(ServletConfig config)
throws ServletException {

super.init(config);

}