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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><title>org.snmp4j</title><!--/*_############################################################################ _## _## SNMP4J _## _## Copyright 2003-2004 Frank Fock and Jochen Katz (SNMP4J.org) _## _## Licensed under the Apache License, Version 2.0 (the "License"); _## you may not use this file except in compliance with the License. _## You may obtain a copy of the License at _## _## http://www.apache.org/licenses/LICENSE-2.0 _## _## Unless required by applicable law or agreed to in writing, software _## distributed under the License is distributed on an "AS IS" BASIS, _## WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. _## See the License for the specific language governing permissions and _## limitations under the License. _## _##########################################################################*/--></head><body bgcolor="white">Provides classes and interfaces for creating, sending, and receiving SNMPmessages.<p>The <code>org.snmp4j</code> classes are capable of creating, sending, andreceiving SNMPv1/v2c/v3 messages. A SNMP message is composed of its messageheader and its PDU payload. This package contains three main groups of classesand interfaces:<ul><li>Classes for SNMP message and target creation<li>Classes for SNMP message sending (command generation)<li>Classes for SNMP message dispatching (command responding)</ul><p>The following UML package diagram illustrates the dependencies between thepackages of the core SNMP4J API. Users of the API normally only need to use the<code>org.snmp4j</code> and the <code>org.snmp4j.smi</code> packages directly.</p><img name="SNMP4J UML Package Diagram" src="doc-files/packages.gif" alt="SNMP4J UML Package Diagram"/><p> The following UML class diagram shows the most important classes of the org.snmp4j package and their relationships (relationships to other packages are not shown):.</p><img name="UML Class Diagram org.snmp4j" src="doc-files/org_snmp4j.gif" alt="UML Class Diagram org.snmp4j"/><h2>SNMP Messages and Targets</h2><p>To exchange a SNMP message with a remote system, that system has to be identified,retransmission, and timeout policy information about the message exchange hasto be specified. A remote system is specified with SNMP4J by creating a<code>Target</code> instance appropriate for the SNMP protocol to be used.</p><p/> <ul> <li>For SNMPv1 and SNMPv2c the <code>CommunityTarget</code> has to be used which provides community information in addition to the address, retransmission, and timeout policy information defined by the <code>Target</code> interface. </li> <li> For SNMPv3 the <code>UserTarget</code> has to be used instead. It extends the <code>SecureTarget</code> abstract class and provides the following User Based Security Model (USM) user information: security name, security level, security model (i.e. USM), and authoritative engine ID. </li> </ul><p/>A SNMP message consists of the message's payload, the SNMP Protocol Data Unit(PDU) and a message header. Simplified said, in SNMP4J the message headerinformation is represented by <code>Target</code> instances and the PDU isrepresented by one of the following classes:<ul> <li> <code>PDUv1</code> (SNMPv1) </li> <li> <code>PDU</code> (SNMPv2c) </li> <li> <code>ScopedPDU</code> (SNMPv3) </li></ul>Thus, in order to be able to send a SNMP message with SNMP4J, a <code>PDU</code>instance and a <code>Target</code> instance have to be created.<h4>PDU Examples</h4><ul> <li>SNMPv1/v2c GETNEXT PDU <pre>import org.snmp4j.PDU;import org.snmp4j.smi.*;...PDU pdu = new PDU();pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.1.1"))); // sysDescrpdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.1"))); // ifNumberpdu.setType(PDU.GETNEXT);... </pre> </li> <li>SNMPv3 GETBULK PDU <pre>import org.snmp4j.ScopedPDU;import org.snmp4j.smi.*;...ScopedPDU pdu = new ScopedPDU();pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.1"))); // ifNumberpdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.2.1.10"))); // ifInOctetspdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.2.1.16"))); // ifOutOctetspdu.setType(PDU.GETBULK);pdu.setMaxRepetitions(50);// Get ifNumber only oncepdu.setNonRepeaters(1);// set context non-default context (default context does not need to be set)pdu.setContextName(new OctetString("subSystemContextA"));// set non-default context engine ID (to use targets authoritative engine ID// use an empty (size == 0) octet string)pdu.setContextEngineID(OctetString.fromHexString("80:00:13:70:c0:a8:01:0d"));... </pre> </li> <li>SNMPv1 TRAP PDU <pre>import org.snmp4j.PDUv1;...PDUv1 pdu = new PDUv1();pdu.setType(PDU.V1TRAP);pdu.setGenericTrap(PDUv1.COLDSTART);... </pre> </li> <li>SNMPv2c/SNMPv3 INFORM PDU <pre>import org.snmp4j.ScopedPDU;...ScopedPDU pdu = new ScopedPDU();pdu.setType(PDU.INFORM);// sysUpTimelong sysUpTime = (System.currentTimeMillis() - startTime) / 10;pdu.add(new VariableBinding(SnmpConstants.sysUpTime, new TimeTicks(sysUpTime)));pdu.add(new VariableBinding(SnmpConstants.snmpTrapOID, SnmpConstants.linkDown));// payloadpdu.add(new VariableBinding(new OID("1.3.6.1.2.1.2.2.1.1"+downIndex), new Integer32(downIndex)));... </pre> </li></ul><h4>Target Examples</h4><ul> <li>Community Target <pre>CommunityTarget target = new CommunityTarget();target.setCommunity(new OctetString("public"));target.setAddress(targetAddress);target.setVersion(SnmpConstants.version1); </pre> </li> <li>User Target <pre>UserTarget target = new UserTarget();target.setAddress(targetAddress);target.setRetries(1);// set timeout to 500 milliseconds -> 2*500ms = 1s total timeouttarget.setTimeout(500);target.setVersion(SnmpConstants.version3);target.setSecurityLevel(SecurityLevel.AUTH_PRIV);target.setSecurityName(new OctetString("MD5DES")); </pre> </li></ul><h2>Sending SNMP messages</h2><p> SNMP message are sent with SNMP4J by using a instance of the SNMP <code>Session</code> interface. The default implementation of this interface is the <code>Snmp</code> class.</p><p> To setup a <code>Snmp</code> instance it is sufficient to call its constructor with a <code>TransportMapping</code> instance. The transport mapping is used by the SNMP session to send (and receive) SNMP message to a remote systems by using a transport protocol, for example the User Datagram Protocol (UDP).</p><p> A SNMP4J <code>Snmp</code> instance supports SNMP v1, v2c, and v3 by default. By sub-classing <code>Snmp</code> other combinations of those SNMP protocol versions can be supported.</p><p> With SNMP4J, SNMP messages can be sent <i>synchronously</i> (blocking) and <i>asynchronously</i> (non-blocking). The <code>Snmp</code> class does not use an internal thread to process responses on asynchronous and synchronous requests. Nevertheless it uses the receiver threads of the transport mappings to process responses.</p><p> Asynchronous responses are returned by calling a callback method on an object instance that implements the <code>ResponseListener</code> interface. The callback is carried out on behalf of the transport mapping thread that received the response packet from the wire. Thus, if the called method blocks, the delivery of synchronous and asynchronous messages received on the listen port of that transport mapping will be also blocked. Other transport mapping will not be affected. Blocking can be avoided by either using synchronous messages only or by decoupling the processing within the callback method.</p><h4>Example for Sending a Synchronous Message</h4><pre>import org.snmp4j.*;...Snmp snmp = new Snmp(new DefaultUdpTransportMapping());...ResponseEvent response = snmp.send(requestPDU, target);if (response.getResponse() == null) { // request timed out ...}else { System.out.println("Received response from: "+ response.getPeerAddress()); // dump response PDU System.out.println(response.getResponse().toString());}</pre><h4>Example for Sending an Asynchronous Message</h4><pre>import org.snmp4j.*;import org.snmp4j.event.*;...Snmp snmp = new Snmp(new DefaultUdpTransportMapping());...ResponseListener listener = new ResponseListener() { public void onResponse(ResponseEvent event) { PDU response = event.getResponse(); PDU request = event.getRequest(); if (response == null) { System.out.println("Request "+request+" timed out"); } else { System.out.println("Received response "+response+" on request "+ request); }};snmp.sendPDU(request, target, null, listener);...</pre><h2>Receiving SNMP messages</h2><p> SNMP4J receives SNMP messages through the listen port of transport mappings. In order to be able to receive responses or requests, that port needs to be set into listen mode. This has to be done by calling the <code>listen()</code> method of the <code>TransportMapping</code> instance to start the transport mappings internal listen thread. The internal thread is stopped and the listen port is closed by calling the <code>close()</code> method on the <code>TransportMapping</code> instance or the associated <code>Snmp</code> instance.</p><p> The transport mapping just receives the SNMP mesage as a stream of bytes and forwards the message to associated <code>MessageDispatcher</code> instances. By default, SNMP4J uses one instance of the <code>MessageDispatcherImpl</code> class for decoding and dispatching incoming messages. That instance is created and used internally by the <code>Snmp</code> class.</p><p> The <code>Snmp</code> class processes responses to outstanding requests and forwards PDUs of other SNMP messages to registered <code>CommandResponder</code> listener instances. To receive SNMP messages it is thus sufficient to <ol> <li> Create a <code>TransportMapping</code> and initialize its listen port by calling <code>TransportMapping.listen()</code>. </li> <li> Create a <code>Snmp</code> instance with the above <code>TransportMapping</code>. </li> <li> Instantiate a class that implements the <code>CommandResponder</code> interface and register it with the <code>Snmp</code> instance by calling <code>Snmp.addCommandResponder(CommandResponder)</code>. </li> </ol><p> When a unhandled SNMP message (thus a SNMP message where no corresponding outstanding request exists) is received, then the <code>processPdu(CommandResponderEvent)</code> method of the <code>CommandResponder</code> will be called with the decoded PDU and additional information about the received SNMP message provided by the message processing model that has decoded the SNMP message.</p><h4>Example for Receiving SNMP Messages</h4><pre>import org.snmp4j.*;import org.snmp4j.smi.*;import org.snmp4j.mp.SnmpConstants;...TransportMapping transport = new DefaultUdpTransportMapping(new UdpAddress("0.0.0.0/161"));Snmp snmp = new Snmp(transport);if (version == SnmpConstants.version3) { byte[] localEngineID = ((MPv3)snmp.getMessageProcessingModel(MessageProcessingModel.MPv3)).createLocalEngineID(); USM usm = new USM(SecurityProtocols.getInstance(), new OctetString(localEngineID), 0); SecurityModels.getInstance().addSecurityModel(usm); snmp.setLocalEngine(localEngineID, 0, 0); // Add the configured user to the USM ...}snmp.addCommandResponder(this);transport.listen();...public synchronized void processPdu(CommandResponderEvent e) { PDU command = e.getPdu(); if (command != null) { ... }}</pre></body></html>⌨️ 快捷键说明
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