Client Implementation

Listing 6.7 InfoClient.java

import javax.swing.*;
import java.rmi.*; 
import java.rmi.registry.*;
import java.awt.*;

//Client implementation
public class InfoClient 
	extends JFrame { 

  String message = "blank"; 

  //Remote reference
  InfoInterface obj = null; 

  //Constructor
  public InfoClient() { 
 	super("Dynamic Loading");
	
	//Text area to show messages
	JTextArea txtArea = new JTextArea(10,35);
	
	//set the font of the component
	txtArea.setFont(new Font("Serif",Font.BOLD,16));
	
	//add the component to the content pane
	getContentPane().add(txtArea);
	try { 

	 //To run this application, change the "servermachinename" to a 
	 //valid machine name. To test without a network specify 
	 //"localhost".
     obj = (InfoInterface)
               Naming.lookup("rmi://servermachinename:1099/Server");
	 
	 //call the remote method
	 message = obj.getInfo(); 

	//Show the message returned
	 txtArea.setText(message);

	} catch (Exception e) { 
	    txtArea.setText("Error : "+e.getMessage()); 
	} 
	 
	 //pack() causes the window to be sized to fit the 
	 //preferred size and layouts of its subcomponents. 
	 pack();
	 
	 //Move the component to the specified location
	 setLocation(10,10);
	 show();
} 

 //main method
 public static void main(String args[]){
     if (System.getSecurityManager() == null) { 
	RMISecurityManager manager = new RMISecurityManager();
		
	//set the security manager
	System.setSecurityManager(manager); 
     }
    new InfoClient();
  }
}

Explanation

The most involved method of the InfoClient class is the main method. The main method installs a security manager. A security manager protects access to system resources from untrusted downloaded code running within the virtual machine. The security manager determines whether downloaded code has access to the local file system, or it can perform any other privileged operations. RMI(s) class loader will not download any classes from remote locations, if no security manager has been set. The following lines install a security manager.

if (System.getSecurityManager() == null) { 
   RMISecurityManager manager = new RMISecurityManager();
   System.setSecurityManager(manager); 
} 

Finally, the main method creates an instance of the InfoClient class.