Development Is Nothing: Database Connection Pooling in Tomcat using Eclipse

Database Connection Pooling is a great technique used by lot of application servers to optimize the performance. Database Connection creation is a costly task thus it impacts the performance of application. Hence lot of application server creates a database connection pool which are pre initiated db connections that can be leverage to increase performance.

Apache Tomcat also provide a way of creating DB Connection Pool. Let us see an example to implement DB Connection Pooling in Apache Tomcat server. We will create a sample web application with a servlet that will get the db connection from tomcat db connection pool and fetch the data using a query. We will use Eclipse as our development environment. This is not a prerequisite i.e. you may want to use any IDE to create this example.

Step 1: Create Dynamic Web Project in Eclipse

Create a Dynamic Web Project in Eclipse by selecting:
File -> New -> Project… ->Dynamic Web Project.
dynamic-project-eclipse

Step 2: Create context.xml

Apache Tomcat allow the applications to define the resource used by the web application in a file called context.xml (from Tomcat 5.x version onwards). We will create a file context.xml under META-INF directory.
db-connection-pooling-eclipse
Copy following content in the context.xml file.

<?xml version="1.0" encoding="UTF-8"?>
<Context>
    <!-- Specify a JDBC datasource -->
    <Resource name="jdbc/testdb" auth="Container"
        type="javax.sql.DataSource" username="DB_USERNAME" password="DB_PASSWORD"
        driverClassName="oracle.jdbc.driver.OracleDriver"
        url="jdbc:oracle:thin:@xxx:1525:dbname"
        maxActive="10" maxIdle="4" />
 
</Context>
  

In above code snippet, we have specify a database connection pool. The name of the resource is jdbc/testdb. We will use this name in our application to get the data connection. Also we specify db username and password and connection URL of database. Note that I am using Oracle as the database for this example. You may want to change this Driver class with any of other DB Providers (like MySQL Driver Class).

Step 3: Create Test Servlet and WEB xml entry

Create a file called TestServlet.java. I have created this file under package: net.viralpatel.servlet. Copy following code into it.

package net.viralpatel.servlet;
 
  import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
 
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
 
  public class TestServlet extends HttpServlet {
   
    private DataSource dataSource;
      private Connection connection;
    private Statement statement;
 
    public void init() throws ServletException {
        try {
            // Get DataSource
            Context initContext  = new InitialContext();
            Context envContext  = (Context)initContext.lookup("java:/comp/env");
            dataSource = (DataSource)envContext.lookup("jdbc/testdb");
 
        } catch (NamingException e) {
            e.printStackTrace();
        }
    }
 
    public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
   
        ResultSet resultSet = null;
          try {
            // Get Connection and Statement
            connection = dataSource.getConnection();
            statement = connection.createStatement();
            String query = "SELECT * FROM STUDENT";
            resultSet = statement.executeQuery(query);
            while (resultSet.next()) {
                System.out.println(resultSet.getString(1) + resultSet.getString(2) + resultSet.getString(3));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            try { if(null!=resultSet)resultSet.close();} catch (SQLException e)
            {e.printStackTrace();}
            try { if(null!=statement)statement.close();} catch (SQLException e)
            {e.printStackTrace();}
            try { if(null!=connection)connection.close();} catch (SQLException e)
            {e.printStackTrace();}
        }
    }
}
  

In the above code we initiated the datasource using InitialContext lookup:

    Context initContext  = new InitialContext();
Context envContext  = (Context)initContext.lookup("java:/comp/env");
dataSource = (DataSource)envContext.lookup("jdbc/testdb");
 

Create test servlet mapping in the web.xml file (deployment descriptor) of the web application. The web.xml file will look like:

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4"
    xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
    <display-name>TomcatConnectionPooling</display-name>
    <welcome-file-list>
          <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
   
    <servlet>
          <servlet-name>TestServlet</servlet-name>
        <servlet-class>
              net.viralpatel.servlet.TestServlet
        </servlet-class>
    </servlet>
      <servlet-mapping>
        <servlet-name>TestServlet</servlet-name>
        <url-pattern>/servlet/test</url-pattern>
    </servlet-mapping>
  </web-app>

Now Run the web application in Tomcat using Eclipse (Alt + Shift + X, R). You will be able to see the result of the query executed.
db-connection-run-project-eclipse
Thus this way we can create a database pool in Tomcat and get the connections from it.