JAVA EE: JDBC|Servlets : Tomcat Connection Pooling - DBCP

Thursday, 30 April 2015

JDBC|Servlets : Tomcat Connection Pooling - DBCP - Mysql

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What is Apache Commons DBCP in Tomcat?

Apache Commons DBCP (Database Connection Pooling) is the default connection pooling implementation packaged with Apache Tomcat. Instead of creating and tearing down database connections on every client request, DBCP manages a pool of active connections. Servlets can quickly borrow, utilize, and return connections to the pool, drastically improving web application performance and throughput.

Step 1: Add the MySQL JDBC Driver to Tomcat

Because Tomcat bundles DBCP natively inside tomcat-dbcp.jar, you only need to ensure the MySQL Connector driver JAR is present in your server's classpath:

Copy mysql-connector-java.jar into the Tomcat/lib directory.
Restart your Tomcat server so it can load the MySQL driver class.

Step 2: Configure DBCP DataSource in context.xml

Define the DBCP DataSource resource in your web application's META-INF/context.xml file:

    <Resource name="jdbc/mysqldb"

      auth="Container"

      type="javax.sql.DataSource"

      factory="org.apache.tomcat.dbcp.dbcp2.BasicDataSourceFactory"

      driverClassName="com.mysql.jdbc.Driver"

      url="jdbc:mysql://localhost:3306/testdb"

      username="root"

      password="root"

      maxTotal="20"

      maxIdle="10"

      minIdle="5"

      maxWaitMillis="10000" />

Step 3: Declare the Resource Reference in web.xml

Add the resource reference inside your web.xml deployment descriptor to map the JNDI lookup name:

    <resource-ref>

      <description>MySQL DBCP Connection Pool</description>

      <res-ref-name>jdbc/mysqldb</res-ref-name>

      <res-type>javax.sql.DataSource</res-type>

      <res-auth>Container</res-auth>

    </resource-ref>

Step 4: Retrieve Connection and Execute Query in Servlet

In your Java Servlet, look up the DataSource via JNDI and execute queries with automatic resource cleanup:

    Context initContext = new InitialContext();

    Context envContext = (Context) initContext.lookup("java:comp/env");

    DataSource ds = (DataSource) envContext.lookup("jdbc/mysqldb");

    try (Connection conn = ds.getConnection();

         Statement stmt = conn.createStatement();

         ResultSet rs = stmt.executeQuery("SELECT user_id, username, email FROM users")) {

      while (rs.next()) {

        out.println(rs.getInt("user_id") + " : " + rs.getString("username"));

      }

    }

📺 Related Connection Pooling Tutorials

Learn more about database architectures and connection pools from our channel:

Click here to watch in Youtube : https://www.youtube.com/watch?v=sXtfWahVEvk&list=UUhwKlOVR041tngjerWxVccw&index=3

Click the below Image to Enlarge

JDBC|Servlets : Tomcat Connection Pooling - DBCP - Mysql

CityInfoServlet.java

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

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 CityInfoServlet 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/worldDB");
            
            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 = "City Information From Mysql Database";
        out.print("<html><body bgcolor=\"#f0f0f0\">");
        out.print("<h1 align=\"center\">" + title + "</h1>\n");
        
        showCityInformation(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 showCityInformation( PrintWriter out )
    {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try
        {

            String sql = "select * from city limit ?";

            /*
             *  Get connection from the DataSource
             */
            
            connection = dataSource.getConnection();
            
            /*
             * Execute the query
             */
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1, 10);

            ResultSet rs = preparedStatement.executeQuery();

            while( rs.next() )
            {
                int id = rs.getInt(1);
                String name = rs.getString(2);
                String countryCode = rs.getString(3);
                String district = rs.getString(4);
                int population = rs.getInt(5);

                /*
                 * Display values
                 */
                out.print("ID: " + id + "<br>");
                out.print("Name: " + name+ "<br>");
                out.print("CountryCode: " + countryCode+ "<br>");
                out.print("District: " + district+ "<br>");
                out.println("Population: " + population+ "<br>");
                out.println("--------------------------------------"+ "<br>");
            }

            rs.close();

        }

        catch( Exception e )
        {
            e.printStackTrace();
        }
        finally
        {
            /*
             * finally block used to close resources
             */
            try
            {
                if( preparedStatement != null )
                {
                    preparedStatement.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>City Info Demo</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>cityInfoServlet</servlet-name>
        <servlet-class>CityInfoServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>cityInfoServlet</servlet-name>
        <url-pattern>/cityInfo</url-pattern>
    </servlet-mapping>

    <resource-ref>
        <description>DB Connection</description>
        <res-ref-name>jdbc/worldDB</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>City Information</title>
</head>
<body>
<p>
<h3>Show City Information</H3>
<p></p>
<ul>

<li><a href="cityInfo">Show City Information</a></li>

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

To Download CityInfoDemoTomcatDBCPMysqlApp Project Click the below link

https://sites.google.com/site/javaee4321/jdbc/CityInfoDemoTomcatDBCPMysqlApp.zip?attredirects=0&d=1

External Links:

http://commons.apache.org/proper/commons-dbcp/configuration.html

http://tomcat.apache.org/tomcat-7.0-doc/jndi-datasource-examples-howto.html

See also:

All JavaEE Viedos Playlist

All JavaEE Viedos

Servlets Tutorial

All Design Patterns Links

JDBC Tutorial

Java Collection Framework Tutorial

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