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.

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.

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.

Thus this way we can create a database pool in Tomcat and get the connections from it.