10.2.2 Looking up the Connector Server

The following code examples are taken from the Client class in the examplesDir/current/Lookup/slp directory.

Example 10–3 Retrieving the List of Connector Servers

public class Client { 
 
    public final static String JMX_SCOPE = "DEFAULT"; 
 
    public static Locator getLocator() throws ServiceLocationException { 
      final Locator slpLocator = 
          ServiceLocationManager.getLocator(Locale.US); 
      return slpLocator; 
    } 
     
      public static List lookup(Locator slpLocator, String name) 
          throws IOException, ServiceLocationException { 
 
   
          final ArrayList list = new ArrayList(); 
          Vector scopes = new Vector(); 
 
          scopes.add(JMX_SCOPE); 
          String query =  
              "(&(AgentName=" + ((name!=null)?name:"*") + "))"; 
 
          ServiceLocationEnumeration result = 
              slpLocator.findServices(new ServiceType("service:jmx"), 
                                      scopes, query); 
 
          while(result.hasMoreElements()) { 
                final ServiceURL surl = (ServiceURL) result.next(); 
                 
 
             JMXServiceURL jmxUrl = new JMXServiceURL(surl.toString()); 
             try { 
                  JMXConnector client = 
                     JMXConnectorFactory.newJMXConnector(jmxUrl,null); 
                  if (client != null) list.add(client); 
             } catch (IOException x ) {  
             [...] 
             } 
          } 
      } 
      return list; 
    } 

Example 10–3 first of all obtains the SLP service Locator by calling the getLocator method of the SLP class ServiceLocationManager. Client then retrieves all the connector servers registered in the SLP service under a given agent name, or under agent names that match a certain pattern. If no agent name is specified when the Client is started, all agent names will be considered.

A JMX Remote API service URL, jmxUrl, is generated for each of the agents retrieved by SLP, with each agent's SLP service URL, surl, passed as a parameter into the JMXServiceURL instance. The URL jmxUrl is then passed to the newJMXConnector() method of JMXConnectorFactory, to create a new connector client named client for each agent that is registered in the SLP service.

The connector clients retrieved are stored in an array list called list.

Example 10–4 Accessing the MBeans in the Remote MBean Server

public static void listMBeans(MBeanServerConnection server) 
     throws IOException { 
 
     final Set names = server.queryNames(null,null); 
     for (final Iterator i=names.iterator(); i.hasNext(); ) { 
          ObjectName name = (ObjectName)i.next(); 
          System.out.println("Got MBean: "+name); 
          try { 
               MBeanInfo info = 
                  server.getMBeanInfo((ObjectName)name); 
               MBeanAttributeInfo[] attrs = info.getAttributes(); 
               if (attrs == null) continue; 
               for (int j=0; j<attrs.length; j++) { 
                    try { 
                         Object o = 
                         server.getAttribute(name,attrs[j].getName()); 
                         System.out.println("\t\t" + attrs[j].getName() + 
                         " = "+o); 
                    } catch (Exception x) { 
                         System.err.println("JmxClient failed to get " + 
                                             attrs[j].getName() + x); 
                         x.printStackTrace(System.err); 
                    } 
     } 
} 
 

In Example 10–4, a reference to the MBeanServerConnection is retrieved for every connector client that is created from the connector server address stored in the SLP service. A list of all the MBeans and their attributes is retrieved.

Example 10–5 Connecting to the Remote Agents

public static void main(String[] args) { 
      try { 
           final String agentName = System.getProperty("agent.name"); 
           final Locator slpLocator = getLocator(); 
           List l = lookup(slpLocator,agentName); 
           int j = 1; 
           for (Iterator i=l.iterator();i.hasNext();j++) { 
                JMXConnector c1 = (JMXConnector) i.next(); 
                if (c1 != null) { 
                    try { 
                         c1.connect(env); 
                    } catch (IOException x) { 
                         System.err.println ("Connection failed: " + x); 
                         x.printStackTrace(System.err); 
                         continue; 
                    } 
 
                    MBeanServerConnection conn = 
                         c1.getMBeanServerConnection(); 
 
                    try { 
                         listMBeans(conn); 
                    } catch (IOException x) { 
                         x.printStackTrace(System.err); 
                    } 
                    try { 
                         c1.close(); 
                    } catch (IOException x) { 
                         x.printStackTrace(System.err); 
                    } 
                } 
           } 
      } catch (Exception x) { 
           x.printStackTrace(System.err); 
      } 
} 

In Example 10–5, the agent.name property is retrieved by calling the getProperty() method of the System class, and the SLP lookup service is found by calling the getLocator() method of Locator.

All the agents named agentName are then looked up, and connections are made to the agents discovered. If no agent is specified, then all agents are lookup up. Connections are made to the MBean server created by Server, and all the MBeans in it are listed, before the connection is closed down.