JAVA EE: JDBC|Servlets : Tomcat Connection Pooling

Thursday 30 April 2015

JDBC|Servlets : Tomcat Connection Pooling - DBCP- Oracle

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JDBC|Servlets : Tomcat Connection Pooling - DBCP- Oracle

EmployeeInfoServlet.java

import java.io.IOException;
import java.io.PrintWriter;
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.servlet.ServletConfig;
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 EmployeeInfoServlet extends HttpServlet
{

    private static final long serialVersionUID = 1L;

    DataSource                dataSource       = null;

    public void init( ServletConfig config )
    {
        try
        {

            System.out
                    .println("-----------------------------------------------------");
            System.out
                    .println("init method has been called and servlet is initialized");

            /*
             * Using JDNI lookup get the DataSource.
             */

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

            System.out.println("Using JDNI lookup got the DataSource : "
                    + dataSource);

            System.out
                    .println("-----------------------------------------------------");
        }

        catch( Exception exe )
        {
            exe.printStackTrace();
        }

    }

    public void doGet( HttpServletRequest request, HttpServletResponse response )
            throws ServletException, IOException
    {

        System.out
                .println("-----------------------------------------------------");
        System.out.println("doGet method has been called");
        System.out
                .println("-----------------------------------------------------");

        response.setContentType("text/html");

        PrintWriter out = response.getWriter();
        String title = "Employee Information From Oracle Database";
        out.print("<html><body bgcolor=\"#f0f0f0\">");
        out.print("<h1 align=\"center\">" + title + "</h1>\n");

        showEmployeeInformation(out);

        out.print("</body></html>");
    }

    public void destroy()
    {
        System.out
                .println("-----------------------------------------------------");
        System.out
                .println("destroy method has been called and servlet is destroyed");
        System.out
                .println("-----------------------------------------------------");
    }

    private void showEmployeeInformation( PrintWriter out )
    {
        Connection connection = null;
        Statement stmt = null;
        try
        {

            /*
             * Get connection from the DataSource
             */

            connection = dataSource.getConnection();

            /*
             * Execute the Query
             */

            stmt = connection.createStatement();
            String sql = "select employee_id,first_name,last_name,email,phone_number from employees";
            ResultSet rs = stmt.executeQuery(sql);

            /*
             * Iterate the ResultSet and get each row Information.
             */
            while( rs.next() )
            {
                /*
                 * Retrieve by column name
                 */
                int id = rs.getInt("employee_id");
                String firstName = rs.getString("first_name");
                String lastName = rs.getString("last_name");
                String email = rs.getString("email");
                String phoneNumber = rs.getString("phone_number");

                /*
                 * Display values
                 */
                out.print("employee_id: " + id+"<br>");
                out.print("first_name: " + firstName+"<br>");
                out.print("last_name: " + lastName+"<br>");
                out.print("email: " + email+"<br>");
                out.println("phone_number: " + phoneNumber+"<br>");
                out.println("-------------------------------------------");
            }
            rs.close();

        }

        catch( Exception e )
        {
            e.printStackTrace();
        }
        finally
        {
            /*
             * finally block used to close resources
             */
            try
            {
                if( stmt != null )
                {
                    stmt.close();
                }
            }
            catch( SQLException sqlException )
            {
                sqlException.printStackTrace();
            }
            try
            {
                if( connection != null )
                {
                    connection.close();
                }
            }
            catch( SQLException sqlException )
            {
                sqlException.printStackTrace();
            }
        }

    }

}

web.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    metadata-complete="true" version="3.0">
    <display-name>EmployeeInfoDemo</display-name>
    <description>
        This is a simple web application with a source code organization
        based on the recommendations of the Application Developer's Guide.
    </description>
    <servlet>
        <servlet-name>employeeInfoServlet</servlet-name>
        <servlet-class>EmployeeInfoServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>employeeInfoServlet</servlet-name>
        <url-pattern>/employeeInfo</url-pattern>
    </servlet-mapping>

    <resource-ref>
        <description>DB Connection</description>
        <res-ref-name>jdbc/HRDB</res-ref-name>
        <res-type>javax.sql.DataSource</res-type>
        <res-auth>Container</res-auth>
    </resource-ref>

</web-app>

index.html

<!DOCTYPE HTML><html lang="en"><head>
<meta charset="UTF-8">
<title>Employee Information</title>
</head>
<body>
<p>
<h3>Employee Information</H3>
<p></p>
<ul>

<li><a href="employeeInfo">Show Employee Information</a></li>

</ul>
</body></html>