package database;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import com.mysql.jdbc.Statement;

public class DatabaseConnection {
	   // JDBC driver name and database URL
	   private final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
	   private String DB_URL = "jdbc:mysql://localhost/";
	   private String DB_NAME;
	   private Connection connection = null;

	   //  Database credentials
	   static final String USER = "user";
	   static final String PASS = "pass";

	   public DatabaseConnection(String databaseName) {
		   DB_NAME = databaseName;
		   DB_URL = DB_URL + DB_NAME;
	   }

	   public Connection getConnection() {
		   if (connection == null) {
			  connection = getNewConnection();
		   }

		   return connection;
	   }


	   public Connection getNewConnection() {
		   try{
			      //STEP 2: Register JDBC driver
			      Class.forName("com.mysql.jdbc.Driver");

			      //STEP 3: Open a connection
			      System.out.println("Connecting to database...");
			      connection = DriverManager.getConnection(DB_URL,USER,PASS);
			      System.out.println("Connected successfully");
			      return connection;

			   }catch(SQLException se){
			      //Handle errors for JDBC
			      se.printStackTrace();
			   }catch(Exception e){
			      //Handle errors for Class.forName
			      e.printStackTrace();
			   }
			  return null;
	   }


	   public static void main(String[] args) {

		   DatabaseConnection db = new DatabaseConnection("students");
		   Connection conn = db.getConnection();

		   Statement stmt = null;
		   try{
		      //STEP 4: Execute a query
		      System.out.println("Creating statement...");
		      stmt = (Statement) conn.createStatement();
		      String sql;
		      sql = "SELECT id, name FROM students";
		      ResultSet rs = stmt.executeQuery(sql);

		      //STEP 5: Extract data from result set
		      while(rs.next()){
		         //Retrieve by column name
		         int id  = rs.getInt("id");
//		         int age = rs.getInt("age");
		         String name = rs.getString("name");
//		         Float mark = rs.getFloat("mark");

		         //Display values
		         System.out.print("ID: " + id);
//		         System.out.print(", Age: " + age);
		         System.out.print(", Name: " + name);
//		         System.out.println(", Mark: " + mark);
		      }
		      //STEP 6: Clean-up environment
		      rs.close();
		      stmt.close();
		      conn.close();
		   }catch(SQLException se){
		      //Handle errors for JDBC
		      se.printStackTrace();
		   }catch(Exception e){
		      //Handle errors for Class.forName
		      e.printStackTrace();
		   }finally{
		      //finally block used to close resources
		      try{
		         if(stmt!=null)
		            stmt.close();
		      }catch(SQLException se2){
		      }// nothing we can do
		      try{
		         if(conn!=null)
		            conn.close();
		      }catch(SQLException se){
		         se.printStackTrace();
		      }//end finally try
		   }//end try
		   System.out.println("Goodbye!");
	}//end main

}