org.snmp4j.Snmp

Posted on 2010-01-20 13:27  胡安峰  阅读(790)  评论(0编辑  收藏  举报

  extended by 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 :

 

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

如何实现SNMPv3信息的同步发送,下面举例说明:

  1. // add user to the USM   
  2.     snmp.getUSM().addUser(new OctetString("MD5DES"),   
  3.                          new UsmUser(new OctetString("MD5DES"),   
  4.                                       AuthMD5.ID,   
  5.                                      new OctetString("MD5DESUserAuthPassword"),   
  6.                                       PrivDES.ID,   
  7.                                      new OctetString("MD5DESUserPrivPassword")));   
  8.    // create the target   
  9.     UserTarget target = new UserTarget();   
  10.     target.setAddress(targetAddress);   
  11.     target.setRetries(1);   
  12.     target.setTimeout(5000);   
  13.     target.setVersion(SnmpConstants.version3);   
  14.     target.setSecurityLevel(SecurityLevel.AUTH_PRIV);   
  15.     target.setSecurityName(new OctetString("MD5DES"));   
  16.   
  17.    // create the PDU   
  18.     PDU pdu = new ScopedPDU();   
  19.     pdu.add(new VariableBinding(new OID("1.3.6")));   
  20.     pdu.setType(PDU.GETNEXT);   
  21.   
  22.    // send the PDU   
  23.     ResponseEvent response = snmp.send(pdu, target);   
  24.    // extract the response PDU (could be null if timed out)   
  25.     PDU responsePDU = response.getResponse();   
  26.    // extract the address used by the agent to send the response:   
  27.     Address peerAddress = response.getPeerAddress();   
  28. An asynchronous SNMPv1 request is sent by the following code:    
  29.   
  30.    // setting up target   
  31.     CommunityTarget target = new CommunityTarget();   
  32.     target.setCommunity(new OctetString("public"));   
  33.     target.setAddress(targetAddress);   
  34.     target.setRetries(2);   
  35.     target.setTimeout(1500);   
  36.     target.setVersion(SnmpConstants.version1);   
  37.    // creating PDU   
  38.     PDU pdu = new PDU();   
  39.     pdu.add(new VariableBinding(new OID(new int[] {1,3,6,1,2,1,1,1})));   
  40.     pdu.add(new VariableBinding(new OID(new int[] {1,3,6,1,2,1,1,2})));   
  41.     pdu.setType(PDU.GETNEXT);   
  42.    // sending request   
  43.     ResponseListener listener = new ResponseListener() {   
  44.      public void onResponse(ResponseEvent event) {   
  45.        // Always cancel async request when response has been received   
  46.        // otherwise a memory leak is created! Not canceling a request   
  47.        // immediately can be useful when sending a request to a broadcast   
  48.        // address.   
  49.         ((Snmp)event.getSource()).cancel(event.getRequest(), this);   
  50.         System.out.println("Received response PDU is: "+event.getResponse());   
  51.       }   
  52.     };   
  53.     snmp.sendPDU(pdu, target, null, listener);   
  54.     
  55. //Traps (notifications) and other SNMP PDUs can be received by adding the folling code to the first code snippet above:    
  56.     CommandResponder trapPrinter = new CommandResponder() {   
  57.      public synchronized void processPdu(CommandResponderEvent e) {   
  58.         PDU command = e.getPDU();   
  59.        if (command != null) {   
  60.           System.out.println(command.toString());   
  61.         }   
  62.       }   
  63.     };   
  64.     snmp.addCommandResponder(trapPrinter);   
  65.     
  66.   
  67.   
  68. Version:    
  69. 1.8    
  70. Author:    
  71. Frank Fock   
  72. 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。