Snmp4j编程简介之三：Snmp

Class Snmp

java.lang.Object
  org.snmp4j.Snmp

All Implemented Interfaces:

java.util.EventListener, CommandResponder, Session

     snmp类是SNMP4J的核心，它提供了发送和接收SNMP PDUs的方法，所有的SNMP PDU 类型都可以采用同步或者异步的方式被发送。

 

    Snmp采用独立的传输协议，通过TransportMapping 接口调用addTransportMapping(TransportMapping transportMapping) 方法或者采用默认的构造函数来实现传输映射，以此来实现信息的传输。

 

  下面的代码片段是采用UDP传输方式来实现一个SNMPv3的SNMP session ：

 

Address targetAddress = GenericAddress.parse("udp:127.0.0.1/161");
   TransportMapping transport = new DefaultUdpTransportMapping();
   snmp = new Snmp(transport);
   USM usm = new USM(SecurityProtocols.getInstance(),
                     new OctetString(MPv3.createLocalEngineID()), 0);
   SecurityModels.getInstance().addSecurityModel(usm);
   transport.listen();

Address targetAddress = GenericAddress.parse("udp:127.0.0.1/161");
   TransportMapping transport = new DefaultUdpTransportMapping();
   snmp = new Snmp(transport);
   USM usm = new USM(SecurityProtocols.getInstance(),
                     new OctetString(MPv3.createLocalEngineID()), 0);
   SecurityModels.getInstance().addSecurityModel(usm);
   transport.listen();

 

如何实现SNMPv3信息的同步发送，下面举例说明：

 

 

 

// add user to the USM
   snmp.getUSM().addUser(new OctetString("MD5DES"),
                         new UsmUser(new OctetString("MD5DES"),
                                     AuthMD5.ID,
                                     new OctetString("MD5DESUserAuthPassword"),
                                     PrivDES.ID,
                                     new OctetString("MD5DESUserPrivPassword")));
   // create the target
   UserTarget target = new UserTarget();
   target.setAddress(targetAddress);
   target.setRetries(1);
   target.setTimeout(5000);
   target.setVersion(SnmpConstants.version3);
   target.setSecurityLevel(SecurityLevel.AUTH_PRIV);
   target.setSecurityName(new OctetString("MD5DES"));

   // create the PDU
   PDU pdu = new ScopedPDU();
   pdu.add(new VariableBinding(new OID("1.3.6")));
   pdu.setType(PDU.GETNEXT);

   // send the PDU
   ResponseEvent response = snmp.send(pdu, target);
   // extract the response PDU (could be null if timed out)
   PDU responsePDU = response.getResponse();
   // extract the address used by the agent to send the response:
   Address peerAddress = response.getPeerAddress();
 An asynchronous SNMPv1 request is sent by the following code:

   // setting up target
   CommunityTarget target = new CommunityTarget();
   target.setCommunity(new OctetString("public"));
   target.setAddress(targetAddress);
   target.setRetries(2);
   target.setTimeout(1500);
   target.setVersion(SnmpConstants.version1);
   // creating PDU
   PDU pdu = new PDU();
   pdu.add(new VariableBinding(new OID(new int[] {1,3,6,1,2,1,1,1})));
   pdu.add(new VariableBinding(new OID(new int[] {1,3,6,1,2,1,1,2})));
   pdu.setType(PDU.GETNEXT);
   // sending request
   ResponseListener listener = new ResponseListener() {
     public void onResponse(ResponseEvent event) {
       // Always cancel async request when response has been received
       // otherwise a memory leak is created! Not canceling a request
       // immediately can be useful when sending a request to a broadcast
       // address.
       ((Snmp)event.getSource()).cancel(event.getRequest(), this);
       System.out.println("Received response PDU is: "+event.getResponse());
     }
   };
   snmp.sendPDU(pdu, target, null, listener);

//Traps (notifications) and other SNMP PDUs can be received by adding the folling code to the first code snippet above:
   CommandResponder trapPrinter = new CommandResponder() {
     public synchronized void processPdu(CommandResponderEvent e) {
       PDU command = e.getPDU();
       if (command != null) {
         System.out.println(command.toString());
       }
     }
   };
   snmp.addCommandResponder(trapPrinter);



Version:
1.8
Author:
Frank Fock
translate：avery_leo

// add user to the USM
   snmp.getUSM().addUser(new OctetString("MD5DES"),
                         new UsmUser(new OctetString("MD5DES"),
                                     AuthMD5.ID,
                                     new OctetString("MD5DESUserAuthPassword"),
                                     PrivDES.ID,
                                     new OctetString("MD5DESUserPrivPassword")));
   // create the target
   UserTarget target = new UserTarget();
   target.setAddress(targetAddress);
   target.setRetries(1);
   target.setTimeout(5000);
   target.setVersion(SnmpConstants.version3);
   target.setSecurityLevel(SecurityLevel.AUTH_PRIV);
   target.setSecurityName(new OctetString("MD5DES"));

   // create the PDU
   PDU pdu = new ScopedPDU();
   pdu.add(new VariableBinding(new OID("1.3.6")));
   pdu.setType(PDU.GETNEXT);

   // send the PDU
   ResponseEvent response = snmp.send(pdu, target);
   // extract the response PDU (could be null if timed out)
   PDU responsePDU = response.getResponse();
   // extract the address used by the agent to send the response:
   Address peerAddress = response.getPeerAddress();
 An asynchronous SNMPv1 request is sent by the following code: 

   // setting up target
   CommunityTarget target = new CommunityTarget();
   target.setCommunity(new OctetString("public"));
   target.setAddress(targetAddress);
   target.setRetries(2);
   target.setTimeout(1500);
   target.setVersion(SnmpConstants.version1);
   // creating PDU
   PDU pdu = new PDU();
   pdu.add(new VariableBinding(new OID(new int[] {1,3,6,1,2,1,1,1})));
   pdu.add(new VariableBinding(new OID(new int[] {1,3,6,1,2,1,1,2})));
   pdu.setType(PDU.GETNEXT);
   // sending request
   ResponseListener listener = new ResponseListener() {
     public void onResponse(ResponseEvent event) {
       // Always cancel async request when response has been received
       // otherwise a memory leak is created! Not canceling a request
       // immediately can be useful when sending a request to a broadcast
       // address.
       ((Snmp)event.getSource()).cancel(event.getRequest(), this);
       System.out.println("Received response PDU is: "+event.getResponse());
     }
   };
   snmp.sendPDU(pdu, target, null, listener);
 
//Traps (notifications) and other SNMP PDUs can be received by adding the folling code to the first code snippet above: 
   CommandResponder trapPrinter = new CommandResponder() {
     public synchronized void processPdu(CommandResponderEvent e) {
       PDU command = e.getPDU();
       if (command != null) {
         System.out.println(command.toString());
       }
     }
   };
   snmp.addCommandResponder(trapPrinter);
 


Version: 
1.8 
Author: 
Frank Fock
translate：avery_leo

 

 

 

Snmp类提供了一套有关Snmp的功能接口。具体来讲，就是发送、接受、创建Snmp消息。
    一个Snmp对象是一个Session，而在Snmp4j中，一个Session可以同多个远程设备通信。

（1） Snmp、Target、PDU三者的关系
    Target代表远程设备或者远程实体、PDU代表管理端同Target通信的数据，Snmp就代表管理者管理功能（其实就是数据的收发）的具体执行者。
       打个比方：Target就是你远方的恋人，PDU就是你们之间传递的情书、而Snmp就是负责帮你寄信收信的邮差。

（2）Snmp收发数据的两种方式
    Snmp可以同步、也可异步收发数据。详细见代码示例说明。

（3）Snmp与传输层协议
    Snmp可以定制传输层协议，一般选择udp，也可以选择tcp。详细见代码示例说明。

（4）Snmp与Usm
    创建Snmp用来发送Snmpv3版本的消息时候，一般还要创建USM，将它添加至安全模型管理器（SecriryModels）中，同时还需要向Usm中添加相应的USM用户（UsmUser）。详细见代码示例说明。

代码示例：（摘自Snmp4j的API文档）

（1）创建Snmp
    1）使用UDP传输协议

TransportMapping transport = new DefaultUdpTransportMapping();
   snmp = new Snmp(transport);

     2）使用TCP传输协议

TransportMapping transport = new DefaultTcpTransportMapping();
   snmp = new Snmp(transport);

    3）创建用于Snmpv3的Snmp

// 创建Snmp
   TransportMapping transport =
      new DefaultUdpTransportMapping();
   Snmp snmp = new Snmp(transport);
   if (version == SnmpConstants.version3) {
       byte[] localEngineID =
            ((MPv3)snmp.getMessageProcessingModel(MessageProcessingModel.MPv3)).createLocalEngineID();
       // 创建USM
       USM usm = new USM(SecurityProtocols.getInstance(),
                      new OctetString(localEngineID), 0); 
       // 将USM添加至安全模式管理器中
       // 安全模型管理器采用了单例模式，它内部可以维护为3个安全模型，分别对应Snmp三个版本
       SecurityModels.getInstance().addSecurityModel(usm);
       snmp.setLocalEngine(localEngineID, 0, 0);
       // 添加用户
       snmp.getUSM().addUser(securityName，new UsmUser(securityName,authProtocol,
                            authPassphrase,privProtocol,privPassphrase)); 
     }

（2）同步收发消息

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());
    }

（3）异步收发消息

import org.snmp4j.*;
    import org.snmp4j.event.*;
    ...
    Snmp snmp = new Snmp(new DefaultUdpTransportMapping());
    ...
    // 增加监听器
    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);
     ...

（4）实现trap
       实现trap需要三步：
       1）创建Snmp；
       2）对于listen（）使处于网络监听（实际上是同于网络编程中的Socket监听）；
       3）实现CommandResponder接口的监听器，并且调用Snmp.addCommandResponder(CommandResponder)注册监听器。

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
        ...
    }
    // 注册命令响应监听器
    snmp.addCommandResponder(this);
    transport.listen();
    ...
    // 实现CommandResponder接口
    public synchronized void processPdu(CommandResponderEvent e) {
        PDU command = e.getPdu();
        if (command != null) {
        ...
       }
    }

总结
    Snmp内含了一个消息分发器，消息分发器中内含了处理网络的线程，在使用完后最好调用close（），将其资源回归处理。
    掌握了上面所说的三个概念，基本上可以使用Snmp4j编写Snmp的程序了。  
    有关Snmp4j编程最好也最详细的资料：API文档和源代码。关于使用Snmp4j编写Snmp程序的例子，多线程的例子可以参看源代码 中：org.snmp4j.test包下的MultiThreadedTrapReceiver.java，完整的例子可以参看 org.snmp4j.tools.console包下的SnmpRequest（一个命令行的Snmp管理器）。
    不过，要想快速和深入掌握Snmp编程，最好的办法一定是先弄懂Snmp协议，这方面的资料最权威的就是RFC协议了。