Download Lecture12

CS441
CURRENT TOPICS IN
PROGRAMMING LANGUAGES
Lecture 12
George Koutsogiannakis/ Summer 2011
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Topics
• Servlets used as RMI Client.
– RMI Security needed for Servlet to RMI server
Communications.
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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");
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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 1099.
– Then go ahead and do the remote invocation
and capture the output (still within try block):
String str=r.reverseString(qr);
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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).
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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();
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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……………
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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();
}
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SET UP OF THE
APPLICATION
• Create 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.
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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;
};
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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:1024-65535",
"connect, accept, listen, resolve";
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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 900.
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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.
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Servlet as RMI Over IIOP Client
– Process the data captured by using the proper stream
with the response object.
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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;
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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.
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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).
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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
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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.
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Study Guide
• See examples posted on the course’ s web
site
– ServletRMI.zip and
– ServletRMIoverIIOP.zip
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