previous chapter table of contents next chapter

Finding a Service Immediately

The simplest scenario for a client is that it wants to find a service immediately, use it, and then (perhaps) terminate. The client will be prepared to wait a certain amount of time before giving up. All issues of discovery can be given to the ServiceDiscoveryManager , and the task of finding a service can be given to a method such as lookup() with a wait parameter. The lookup() method will block until a suitable service is found or the time limit is reached. If the time limit is reached, a null object will be returned; otherwise a non- null service object will be returned.

 package client; import common.FileClassifier; import common.MIMEType; import java.rmi.RMISecurityManager; import net.jini.discovery.LookupDiscovery; import net.jini.core.lookup.ServiceTemplate; import net.jini.discovery.LookupDiscoveryManager; import net.jini.lookup.ServiceDiscoveryManager; import net.jini.core.lookup.ServiceItem; import net.jini.lease.LeaseRenewalManager; /**  *ImmediateClientLookup.java  */ public class ImmediateClientLookup {     private static final long WAITFOR = 100000L;     public static void main(String argv[]) {         new ImmediateClientLookup();         // stay around long enough to receive replies         try {             Thread.currentThread().sleep(2*WAITFOR);         } catch(java.lang.InterruptedException e) {             // do nothing         }     }     public ImmediateClientLookup() {         ServiceDiscoveryManager clientMgr = null;         System.setSecurityManager(new RMISecurityManager());         try {             LookupDiscoveryManager mgr =                 new LookupDiscoveryManager(LookupDiscovery.ALL_GROUPS,                                            null /* unicast locators */,                                            null /* DiscoveryListener */);             clientMgr = new ServiceDiscoveryManager(mgr,                                                 new LeaseRenewalManager())         } catch(Exception e) {             e.printStackTrace();             System.exit(1);         }         Class [] classes = new Class[] {FileClassifier.class};         ServiceTemplate template = new ServiceTemplate(null, classes,                                                        null);         ServiceItem item = null;         // Try to find the service, blocking till timeout if necessary         try {             item = clientMgr.lookup(template,                                     null, /* no filter */                                     WAITFOR /* timeout */);         } catch(Exception e) {             e.printStackTrace();             System.exit(1);         }         if (item == null) {             // couldn't find a service in time             System.out.println("no service");             System.exit(1);         }         // Get the service         FileClassifier classifier = (FileClassifier) item.service;         if (classifier == null) {             System.out.println("Classifier null");             System.exit(1);         }         // Now we have a suitable service, use it         MIMEType type;         try {             String fileName;             // Try several file types: .txt, .rtf, .abc             fileName = "file1.txt";             type = classifier.getMIMEType(fileName);             printType(fileName, type);             fileName = "file2.rtf";             type = classifier.getMIMEType(fileName);             printType(fileName, type);             fileName = "file3.abc";             type = classifier.getMIMEType(fileName);             printType(fileName, type);         } catch(java.rmi.RemoteException e) {             System.err.println(e.toString());         }         System.exit(0);     }     private void printType(String fileName, MIMEType type) {         System.out.print("Type of " + fileName + " is ");         if (type == null) {             System.out.println("null");         } else {             System.out.println(type.toString());         }     } } // ImmediateClientLookup 

A Programmer[ap]s Guide to Jini Technology
A Programmer[ap]s Guide to Jini Technology
ISBN: 1893115801
Year: 2000
Pages: 189

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net