Receiving Inform Requests

Managers receive inform requests as they do traps: they are unsolicited events that must be received by a dispatcher object. Unlike traps, an inform request requires a response PDU that, according to the SNMP specification, must contain the same variable bindings. Therefore, immediately after an inform request is successfully received and decoded, the SnmpEventReportDispatcher class automatically constructs and sends the inform response back to the originating host.

The manager application then retrieves the data in the inform request through a listener on the dispatcher. Inform request listeners are registered with the dispatcher object in the same way as trap listeners. The receiving manager in our example is very simple, because its only function is to create the dispatcher and the listener for inform requests. The receiving manager SimpleManager2 is the same for both the SimpleManager1 and SimpleManager1V3 examples.

Example 19–11 Receiving Inform Requests in SimpleManager2

// Initialize the port number to listen for incoming inform PDUs on 
// port 8085.
int port = 8085;

try {
    
    // Create a dispatcher for SNMP event reports 
	   // (SnmpEventReportDispatcher).
    // SnmpEventReportDispatcher is run as a thread and listens for informs
    // on the specified port.
    // Add our InformListenerImpl class as an SnmpInformListener.
    // InformListenerImpl will receive a callback when a valid trap
    // PDU is received.
    //
    SnmpEventReportDispatcher informDispatcher =
        new SnmpEventReportDispatcher(port,taskServer,null,null);
    informDispatcher.addInformListener(new InformListenerImpl());
	   final Thread informThread = new Thread(informDispatcher);
	   informThread.setPriority(Thread.MAX_PRIORITY);    
     informDispatcher.start();
		println("\nNOTE: SNMP simple manager 2 initialized");

    // Note that you can use the same SnmpEventReportDispatcher object
    // for both incoming traps and informs.
    // Just add your trap listener to the same dispatcher, for example:
    //    informDispatcher.addTrapListener(new TrapListenerImpl());

    // Here we are just going to wait for inform PDUs.
    //
    java.lang.System.out.println("\nNOTE: Event report listener 
	   initialized");
    java.lang.System.out.println(
      "      and listening for incoming inform PDUs on port " + port 
		+ "...");

} catch(Exception e) {
    java.lang.System.err.println(
        "SimpleManager2::main: Exception occurred:" + e );
    e.printStackTrace();
}

The remaining step is to program the behavior we want upon receiving an inform request. To do this, we must write the InformListenerImpl class that we registered as an inform request listener in the previous code sample. This class implements the SnmpInformListener interface and its processSnmpInform and processSnmpInformV3 methods handle the incoming inform requests.

Because the dispatcher automatically sends the inform response back to the originating host, the SnmpInformListener implementation does not need to do this. Usually this method extracts the variable bindings and takes whatever action is necessary upon receiving an inform request. In our example, we simply print out the source and the contents of the inform request.

Example 19–12 The InformListenerImpl Class

import java.io.IOException;
import javax.management.snmp.SnmpPduRequest;
import javax.management.snmp.manager.SnmpInformListener;

/**
 * This class implements the SnmpInformListener interface.
 * The callback method processSnmpInform is called when a
 * valid inform PDU is received.
 */

public class InformListenerImpl implements SnmpInformListener {

    public void processSnmpInform(SnmpPduRequest inform) {
        
        // Display the received PDU.
        //
        java.lang.System.out.println("\nNOTE: Inform request received:\n");
        java.lang.System.out.println("\tType
			 = " + inform.pduTypeToString(inform.type));
        java.lang.System.out.println("\tVersion   = " + inform.version);
        java.lang.System.out.println("\tRequestId = " + inform.requestId);
        java.lang.System.out.println("\tAddress   = " + inform.address);
        java.lang.System.out.println("\tPort      = " + inform.port);
        java.lang.System.out.println("\tCommunity = " +
            new String(inform.community));
        java.lang.System.out.println("\tVB list   = ");

        for (int i = 0; i < inform.varBindList.length; i++) {
            java.lang.System.out.println("\t\t" + inform.varBindList[i]);
        }


			public void processSnmpInformV3(SnmpScopedPduRequest inform) {
				println("\nNOTE: Inform request V3 received:\n");
       	 	println("\tType      = 
				" + inform.pduTypeToString(inform.type));
       		println("\tVersion   = " + inform.version);
		      	println("\tRequestId = " + inform.requestId);
     	  	println("\tAddress   = " + inform.address);
        		println("\tPort      = " + inform.port);
        		println("\tContext = " + new String(inform.contextName));
        		println("\tVB list   = ");
        		for (int i = 0; i < inform.varBindList.length; i++) {
           		 println("\t\t" + inform.varBindList[i]);
        }
    }
    
        // Our listener stops the manager after receiving its first
        // inform request
        java.lang.System.out.println(
            "\nNOTE: SNMP simple manager 2 stopped...");
        java.lang.System.exit(0);
    }
}

To Run the SNMPv2 Inform Request Example

The examplesDir/Snmp/Inform directory contains all of the files for the two manager applications, along with the InformListenerImpl class.

1. Compile all files in this directory with the javac command.

   For example, on the Solaris platform with the Korn shell, you would type:

   $ cd examplesDir/Snmp/Inform/ $ javac -classpath classpath *.java

2. To run the example, start the inform request receiver with the following command.

   $ java -classpath classpath SimpleManager2

   You can start the application in another terminal window or on another host.

3. Wait for this manager to be initialized, then start the other manager with the following command.

   The hostname is the name of the host where you started the receiving manager, or localhost.

   $ java -classpath classpath SimpleManager1 hostname

4. When the sender is ready, press Enter to send the inform request.

   You should see the contents of the request displayed by the receiving manager. Immediately afterwards, the sender receives the inform response containing the same variable bindings and displays them. Both manager applications then exit automatically.

To Run the SNMPv3 Inform Request Example

1. Before running the example, you must compile the Java classes in the examplesDir/Snmp/Inform directory.

   Type the following commands in your working directory:

   $ javac -d . SimpleManager1V3.java SimpleManager2.java InformListenerImpl.java

2. Start the receiving manager, SimpleManager2:

   $ java -classpath classpath -Djdmk.security.file=./jdmk.security SimpleManager2

   This manager binds to port 8085.

3. Wait for this manager to be initialized, then start the other manager with the following command, specifying the hostname and port number of the receiving manager.

   In this case, the host name is the localhost

   $ java -classpath classpath -Djdmk.security.file=./sender.security SimpleManager1V3 localhost

4. When the sender is ready, press Enter to send the inform request.

   You should see the contents of the request displayed by the receiving manager. Immediately afterwards, the sender receives the inform response containing the same variable bindings and displays them. Both manager applications then exit automatically.