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.