1 Lecture 12 George Koutsogiannakis/ Summer 2011 CS441 CURRENT TOPICS IN PROGRAMMING LANGUAGES

Topics Servlets used as RMI Client. –RMI Security needed for Servlet to RMI server Communications. 2

Servlet as RMI client The Servlet will implement the doGet or doPost method as normally. Within the method (doGet or doPost): –You need to catch Exceprion (create try/catch) –Do a lookup on the registry: ReverseInterface r= (ReverseInterface) Naming.lookup ("//localhost:1099/Reverse"); 3

Servlet as RMI client –Where we assume that: The server has registered a remote object for its instance called “Reverse”. The server’s Remote Interface that defines its service is ReverseInterface. The registry is at port –Then go ahead and do the remote invocation and capture the output (still within try block): String str=r.reverseString(qr); 4

Servlet as RMI client –Where r is the reference received from the registry –The argument in the remote method is the data type that the method accepts (i.e qr is of String data type in the example). –The returned value from the server is captured by variable str (assuming that the remote method returns a String data type in this example). 5

Servlet as RMI client –Process the captured data by the servlet using the proper stream and the response object: PrintWriter out=response.getWriter(); out.println(str); out.close(); 6

RMI server. Create RMI server as it is done normally. import java.rmi.Remote; import java.rmi.RemoteException; public interface ReverseInterface extends Remote { String reverseString(String originalstring) throws RemoteException; } IN THE SERVER ReserveInterfaceImpl: public static void main(String[] args){ String name="//localhost/Reverse"; try { ReverseInterfaceImpl r= new ReverseInterfaceImpl(); Naming.rebind(name, r); etc…………… 7

RMI server. IMPLEMENT THE REMOTE METHOD (SERVICE) public String reverseString(String originalstring) throws RemoteException { int length=originalstring.length(); StringBuffer temp=new StringBuffer(length); for (int i=length; i>0; i-- ) { temp.append(originalstring.substring(i-1,i)); } return temp.toString(); } 8

SET UP OF THE APPLICATION C reate the applications web site outside of Tomcat (NEVER DEVELOP THE APPLICATION INSIDE TOMCAT). Do NOT Include the required files for the RMI server in the application’s deployment. Place all RMI client related files in the same directory as the servlet. Deploy using a WAR file approach. –Remember that with the servlet you will need the stub from the server and a copy of the interface file also. 9

SET UP OF THE APPLICATION You will need the certificate applied like you did in the assignment 1 with respect to a signed applet –We assume that the servlet uses an applet as a client!! You may need a policy file like (optional): grant { permission java.security.AllPermission; }; 10

SET UP OF THE APPLICATION To allow communications between the Web Server (the servlet acting as RMI client) and the RMI Server: –Modify the java.policy file in the System’s security directory (jdk installation) as follows: // allows anyone to listen on un-privileged ports permission java.net.SocketPermission "localhost: ", "connect, accept, listen, resolve"; 11

Servlet as RMI Over IIOP Client. In either the doGet or doPost method: –We will need a Hashtable structure to place the call to registry as a name/value attributes ReverseInterface r; Hashtable env=new Hashtable(); env.put("java.naming.factory.initial", "com.sun.jndi.cosnaming.CNCtxFactory"); env.put("java.naming.provider.url", "iiop://localhost:900"); We assume that the IIOP Naming Service is listening at port

Servlet as RMI Over IIOP Client –In try block contact the Naming Service (IIOP registry): Context initialNamingContext=new InitialContext(env); out.println("obtained InitialContext"); r=(ReverseInterface)PortableRemoteObject.narrow(initialNami ngContext.lookup("Reverse"), ReverseInterface.class); –Now do the remote invocation using the reference r received from the Naming Service String str=r. reverseString(qr); WHERE reverseString is the remote method defined in the Interface created by the Server. 13

Servlet as RMI Over IIOP Client –Process the data captured by using the proper stream with the response object. 14

RMI Over IIOP Server Need additional import statements: import java.rmi.*; import java.rmi.server.*; //add the lines below import javax.rmi.PortableRemoteObject; import javax.naming.*; import java.net.*; import javax.naming.Context; import javax.naming.InitialContext; import javax.naming.NamingException; 15

RMI Over IIOP Server –public class ReverseInterfaceImpl extends PortableRemoteObject implements ReverseInterface –Registration in try block in main method: ReverseInterfaceImpl r= new ReverseInterfaceImpl(); //add the follwoing lines Context initialNamingContext=new InitialContext(); System.out.println("Binding server to registry.."); initialNamingContext.rebind("Reverse", r); System.out.println("Object was registered"); –Implement the remote method. 16

SET UP OF THE APPLICATION Set up is similar to RMI description in previous files. Compiling should be as described in the RMI over IIOP presentation (lecture 11). 17

RMI SECURITY RMI has its own Security Manager. –Automatic downloading of stub files and interface file by the client is strictly cntrolled by security. Secured Class Loaded java.policy file java.security file Security Policy controlled by RMISecurityManager object 18

RMI SECURITY RMISecurityManager creates a sandbox similar to what the applets have to encounter. Default RMISecurityManager uses the default java.policy and java.security system files. We can create our own RMISecurityManager and remove some of the restrictions. We can also change for demonstration reasons some of the restrictions by modifying the java.policy and java.security files and let the default RMISecurityManager object operate. 19

Study Guide See examples posted on the course’ s web site –ServletRMI.zip and –ServletRMIoverIIOP.zip 20