Server Implementation

The design of the server is simple. The server starts a registry service and registers itself with the registry. It exports methods to add, delete, update, and find records.

Listing 14.2 DatabaseServerImpl.java

import java.rmi.*;
import java.rmi.server.*;
import java.rmi.registry.*;
import java.sql.*;


//server class
public class DatabaseServerImpl extends 
	UnicastRemoteObject implements DatabaseInterface{
	
  //connection to the database;
  private static Connection con = null;

  //static block used to connect to the database
  static
     {
	try{

	//load the driver.
	//Returns the Class object associated 
	//with the class 
	//or interface with the given string name. 
	Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

	//Create a connection with the database.
	//The DriverManager attempts to select 
	//an appropriate driver from the 
	//set of registered JDBC drivers.
	con = DriverManager.getConnection("jdbc:odbc:students");
	}catch(ClassNotFoundException ex){
	  System.out.println
		("Error connecting : \n " +ex.getMessage());
	
	 //exit if driver is not loaded.
	 System.exit(0);
 	}
	catch(SQLException ex){
	  System.out.println
		("Error connecting : \n " +ex.getMessage());
	}
}

//constructor
  public DatabaseServerImpl()
	throws RemoteException,SQLException{
	System.out.println("Creating remote object");
  }

  //method used to add a new record. 
  //The method gets a Student object
  //as its argument.
  public String addRecord(Student std)
	throws RemoteException,SQLException {
		
	//create a query
	String query = "INSERT INTO STUDENTINFO VALUES("+
	std.getRollNumber() + ",'" + 
	std.getName() + "','"+
	std.getCourse()+"')";

	//Create a Statement object for sending SQL 
	//statements to the database.
	Statement stmt=con.createStatement();
	
	//execute the query
	stmt.executeUpdate(query);
	return "Record added.";
   }

  //method used to update a record. 
  //The method gets a Student object
  //as its argument.
   public String updateRecord(Student std)
	throws RemoteException,SQLException {
	
	//create a query
	String query = "UPDATE STUDENTINFO SET NAME= '"+
	std.getName() + "'," +
	" COURSE = '" + std.getCourse()+ "'"+	
	" WHERE ROLLNO = " + std.getRollNumber();	
	
	//Create a Statement object for sending SQL 
	//statements to the database.
	Statement stmt = con.createStatement();

	//execute query
	stmt.executeUpdate(query);

	//return the result
	return "Record updated successfully.";
    }

//method used to delete a record. 
    //The method gets the roll number
    //of the student as parameter.
    public String deleteRecord(int rollNumber)
	throws RemoteException,SQLException {
	
	//create a query
	String query= "DELETE FROM STUDENTINFO "+
	" WHERE ROLLNO = " +
	rollNumber;
	
	//Create a Statement object for sending SQL 
	//statements to the database.
	Statement stmt = con.createStatement();
	
	//Returns the number of rows deleted
	int rows = stmt.executeUpdate(query);
	if(rows == 0)

	  //if no row is deleted
	  return "No matching record found."; 

	//if record is deleted
	return "Record deleted.";
   }

   //Method used to find a record. The method gets 
   //the roll number of the student as parameter.
   public Object findRecord(int rollNumber)
	 throws RemoteException,SQLException{
		
	//create a query
.	String query = "SELECT NAME, COURSE FROM STUDENTINFO"+
		" WHERE ROLLNO = " + rollNumber; 

	//Create a Statement object for sending SQL 
	//statements to the database.
 	Statement stmt = con.createStatement();

	//Executes an SQL statement that returns a single 
	//ResultSet object.
	ResultSet rs = stmt.executeQuery(query); 
	
	//A ResultSet cursor is initially positioned 
	//before the first row; the first call to the method 
	//next makes the first row the current row.
	if(rs.next()){
	
	  //Get the value of the column in the 
	  //current row of this ResultSet object as a String 
	  String name = rs.getString(1);
  	  String course = rs.getString(2);
	
	  //create a new student object.
	  Student std = new Student(rollNumber,name,course);
	 
     //return the object.
  	  return std;
	}

	//if no matching record is found.
	return "Record not found.";
    } 

	
  //main method
  public static void main(String[]args){
 	try{

	//server object
	DatabaseServerImpl obj = new DatabaseServerImpl();

	//Create and export a registry on the local host 
	//that accepts requests on port number 1099.
	Registry reg = LocateRegistry.createRegistry(1099);

	//bind the server object
	 reg.rebind("DatabaseServer",obj);
	}catch(Exception e){
	  System.out.println(e.getMessage());
	}
    }
}