92.

  

Using a Filter

An example in Chapter 13 discussed how to select a printer with a speed greater than a certain value. This type of problem is well suited to the ServiceDiscoveryManager using a ServiceItemFilter . The ServiceItemFilter interface has a check() method, which is called on the client side to perform additional filtering of services. This method can accept or reject a service based on criteria supplied by the client.

The following program illustrates how this check() method can be used to select only printer services with a speed greater than 24 pages per minute:

 package client; import common.Printer; 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; import net.jini.lookup.ServiceItemFilter; /**  * TestPrinterSpeedFilter.java  */ public class TestPrinterSpeedFilter implements ServiceItemFilter {     private static final long WAITFOR = 100000L;     public TestPrinterSpeedFilter() {         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[] {Printer.class};         ServiceTemplate template = new ServiceTemplate(null, classes,                                                        null);          ServiceItem item = null;         try {             item = clientMgr.lookup(template,                                     this, /* filter */                                     WAITFOR /* timeout */);         } catch(Exception e) {             e.printStackTrace();             System.exit(1);         }         if (item == null) {             // couldn't find a service in time             System.exit(1);         }         Printer printer = (Printer) item.service;         // Now use the printer         // ...     }     public boolean check(ServiceItem item) {         // This is the filter         Printer printer = (Printer) item.service;         if (printer.getSpeed() > 24) {             return true;         } else {             return false;         }     }     public static void main(String[] args) {         TestPrinterSpeed f = new TestPrinterSpeed();         // stay around long enough to receive replies         try {             Thread.currentThread().sleep(2*WAITFOR);         } catch(java.lang.InterruptedException e) {             // do nothing         }         } } // TestPrinterSpeed