SNMP4J

使用SNMP4J可以很方便的实现一个SNMP NMS的功能。
对于SNMPv1/SNMPv2，简单的说，只需要以下几个步骤
1) 创建Snmp对象snmp

2) 创建CommunityTarget对象target，并指定community, version, address, timeout, retry等参数。

3) 创建PDU对象pdu，并指定操作类型(GET/GETNEXT/GETBULK/SET)， 添加VariableBinding(也就是待操作的OID),
    如果是GETBULK操作，还可以指定MaxRepetitions和NonRepeaters。
 注意一定要指定MaxRepetitions，默认值是0，那样不会返回任何结果。

4) 调用snmp.send(pdu, target)方法，发送请求请返回结果。

此外，SNMP4J提供了TableUtils类，可以很轻松的实现一个SNMP Walk的功能，比如一次返回一个表格下面的所有MIB值。
TableUtils类还支持指定ower bound index 和 upper bound index， 得到更小范围的结果以提高性能。这一点对于从一个很多行的表中取一部分行的数据来说很重要。

Snmp还支持异步的send方法。

下面的代码实例实现了GET, GETNEXT, GETBULK, Walk, SET操作，
以及一个利用异步send方法实现的agent discovery： 对一个广播地址发送请求，等待agent返回的应答。
如果需要对一个范围内的IP进行扫描，可以稍加改进，反复调用异步send多次发送给不同IP。

 import java.io.IOException;
 import java.util.List;
 import java.util.Vector;

 import org.snmp4j.CommunityTarget;
 import org.snmp4j.PDU;
 import org.snmp4j.Snmp;
 import org.snmp4j.event.ResponseEvent;
 import org.snmp4j.event.ResponseListener;
 import org.snmp4j.mp.SnmpConstants;
 import org.snmp4j.smi.OID;
 import org.snmp4j.smi.OctetString;
 import org.snmp4j.smi.UdpAddress;
 import org.snmp4j.smi.VariableBinding;
 import org.snmp4j.transport.DefaultUdpTransportMapping;
 import org.snmp4j.util.DefaultPDUFactory;
 import org.snmp4j.util.TableEvent;
 import org.snmp4j.util.TableUtils;

 public class SNMPv2Test {
     public static void main(String[] args) throws IOException, InterruptedException {
         Snmp snmp = new Snmp(new DefaultUdpTransportMapping());
         snmp.listen();

         CommunityTarget target = new CommunityTarget();
         target.setCommunity(new OctetString("public"));
         target.setVersion(SnmpConstants.version2c);
         target.setAddress(new UdpAddress("192.168.0.100/161"));
         target.setTimeout(3000);    //3s
         target.setRetries(1);

         sendRequest(snmp, createGetPdu(), target);
         sendRequest(snmp, createGetNextPdu(), target);
         sendRequest(snmp, createGetBulkPdu(), target);
         snmpWalk(snmp, target);

         target.setCommunity(new OctetString("private"));
         sendRequest(snmp, createSetPdu(), target);

         CommunityTarget broadcastTarget = new CommunityTarget();
         broadcastTarget.setCommunity(new OctetString("public"));
         broadcastTarget.setVersion(SnmpConstants.version2c);
         broadcastTarget.setAddress(new UdpAddress("192.168.0.255/161"));
         broadcastTarget.setTimeout(5000);   //5s
         sendAsyncRequest(snmp, createGetNextPdu(), broadcastTarget);
         Thread.sleep(6000); //main thread wait 6s for the completion of asynchronous request
     }

     private static PDU createGetPdu() {
         PDU pdu = new PDU();
         pdu.setType(PDU.GET);
         pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.1.3.0"))); //sysUpTime
         pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.1.5.0"))); //sysName
         pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.1.5")));   //expect an no_such_instance error
         return pdu;
     }

     private static PDU createGetNextPdu() {
         PDU pdu = new PDU();
         pdu.setType(PDU.GETNEXT);
         pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.1.3")));   //sysUpTime
         pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.1.5")));   //sysName

         return pdu;
     }

     private static PDU createGetBulkPdu() {
         PDU pdu = new PDU();
         pdu.setType(PDU.GETBULK);
         pdu.setMaxRepetitions(10);  //must set it, default is 0
         pdu.setNonRepeaters(0);
         pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.1")));     //system
         return pdu;
     }

     private static PDU createSetPdu() {
         PDU pdu = new PDU();
         pdu.setType(PDU.SET);
         pdu.add(new VariableBinding(new OID("1.3.6.1.2.1.1.5.0"), new OctetString("sysname"))); //sysName
         return pdu;
     }

     private static void sendRequest(Snmp snmp, PDU pdu, CommunityTarget target)
     throws IOException {
         ResponseEvent responseEvent = snmp.send(pdu, target);
         PDU response = responseEvent.getResponse();

         if (response == null) {
             System.out.println("TimeOut...");
         } else {
             if (response.getErrorStatus() == PDU.noError) {
                 Vectorextends VariableBinding> vbs = response.getVariableBindings();
                 for (VariableBinding vb : vbs) {
                     System.out.println(vb + " ," + vb.getVariable().getSyntaxString());
                 }
             } else {
                 System.out.println("Error:" + response.getErrorStatusText());
             }
         }
     }

     private static void sendAsyncRequest(Snmp snmp, PDU pdu, CommunityTarget target)
     throws IOException {
         snmp.send(pdu, target, null, new ResponseListener(){

             @Override
             public void onResponse(ResponseEvent event) {
                 PDU response = event.getResponse();
                 System.out.println("Got response from " + event.getPeerAddress());
                 if (response == null) {
                     System.out.println("TimeOut...");
                 } else {
                     if (response.getErrorStatus() == PDU.noError) {
                         Vectorextends VariableBinding> vbs = response.getVariableBindings();
                         for (VariableBinding vb : vbs) {
                             System.out.println(vb + " ," + vb.getVariable().getSyntaxString());
                         }
                     } else {
                         System.out.println("Error:" + response.getErrorStatusText());
                     }
                 }
             }});
     }

     private static void snmpWalk(Snmp snmp, CommunityTarget target) {
         TableUtils utils = new TableUtils(snmp, new DefaultPDUFactory(PDU.GETBULK));//GETNEXT or GETBULK
         utils.setMaxNumRowsPerPDU(5);   //only for GETBULK, set max-repetitions, default is 10
         OID[] columnOids = new OID[] {
                 new OID("1.3.6.1.2.1.1.9.1.2"), //sysORID
                 new OID("1.3.6.1.2.1.1.9.1.3"), //sysORDescr
                 new OID("1.3.6.1.2.1.1.9.1.5")  //wrong OID, expect an null in in VariableBinding array
         };
         // If not null, all returned rows have an index in a range (lowerBoundIndex, upperBoundIndex]
         List l = utils.getTable(target, columnOids, new OID("3"), new OID("10"));
         for (TableEvent e : l) {
             System.out.println(e);
         }
     }
 }