Java Tutorial/Database/DataSource

Look up DataSource from InitialContext

import java.sql.Connection;
import javax.naming.InitialContext;
import javax.sql.DataSource;
public class Main {
  public static void main(String[] argv) throws Exception {
    InitialContext init = new InitialContext();
    DataSource source = (DataSource) init.lookup("dsn");
    Connection connection = source.getConnection();
    System.out.println("Connect to " + connection.getCatalog() + " a success!");
  }
}

Use JNDI to get database connection or data source

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 java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.Servlet;
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 Main extends HttpServlet implements Servlet {
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    DateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy");
    response.setContentType("text/html");
    PrintWriter writer = response.getWriter();
    Connection connection = getConnection();
    if (connection != null) {
      String sql = "SELECT SYSDATE FROM DUAL";
      try{
      PreparedStatement statement = connection.prepareStatement(sql);
      ResultSet rs = statement.executeQuery();
      while (rs.next()) {
        Date date = rs.getDate("SYSDATE");
        writer.println("The current date is " + dateFormat.format(date));
      }
      connection.close();
      }catch(Exception e){
        System.out.println(e);
      }
    }
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
  }
  private Connection getConnection() {
    Connection connection = null;
    try {
      InitialContext context = new InitialContext();
      DataSource dataSource = (DataSource) context.lookup("jdbc/DataSource");
      connection = dataSource.getConnection();
    } catch (NamingException e) {
      e.printStackTrace();
    } catch (SQLException e) {
      e.printStackTrace();
    }
    return connection;
  }
}