Database Connection Pooling in Tomcat using Eclipse

atabase 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: com.vaani.servlet. Copy following code into it.

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>

            com.vaani.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.