大家给看看哪里出了问题,用snmp4j访问mib

package               snmp;       import               java.io.IOException;       
import               java.net.InetAddress;       import               org.snmp4j.CommunityTarget;       
import               org.snmp4j.PDU;       
import               org.snmp4j.Snmp;       
import               org.snmp4j.event.ResponseEvent;       
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;       public   class   test3{                 public   static   void   main(String[]   args)       
                  {       
                        try   {       
                                Snmp   snmp     =     new   Snmp(new     DefaultUdpTransportMapping());       
                                CommunityTarget     target     =     new   CommunityTarget();//agent对象       
                                    target.setCommunity(new   OctetString("public"));//设置共同体名,没发现设置RWCommnity的方       
                                                                                                                //法,大概只能设一个.       
                                target.setVersion(SnmpConstants.version2c);//设置版本       
                                    target.setAddress(new   UdpAddress("127.0.0.1/161"));//设置IP地址和端口号,这里竟然用'/'来   分           
                                        //隔,当初确实没有料到,JDOC的说明等于没有.       
                                target.setRetries(1);       //设置重试次数       
                                    target.setTimeout(5000);     //设置超时       
                                    snmp.listen();     //监听       
                                  PDU   request   =   new   PDU();       //new               request               PDU包       
                                    //set   pud   type   and   set   oid       
                              request.setType(PDU.GET);               //设置PDU类型,       
                            request.add(new   VariableBinding(new   OID(".1.3.6.1.2.1.1.1.0")));               //OID添加       
                              //   request.add(new   VariableBinding(new     OID(".1.3.6.1.2.1.1.2.0")));       
                            System.out.println("request   UDP:"     +       request);//请求包内内容输出,       
                            PDU     response     =       null;//定义response包       
                                ResponseEvent   responseEvent   =   snmp.send(request,target);       //发出request       PDU       
                                                                                                //接收response       PDU       
                            response     =     responseEvent.getReresponse();     //response       PDU包解析       
                              if(response!=null){       
                              if(response.getErrorIndex()==response.noError&&response.getErrorStatus()==response.noError){       
                                      System.out.println("n   error.");       
                                      String     pause=responseEvent.getResponse().getVariableBindings().toString();       
                                      String     getvalue=pause.substring(pause.indexOf("=")+2,pause.indexOf(']'));       
                                      String     oid=pause.substring(pause.indexOf("VBS[")+2,pause.indexOf("=")-1);       
                                      System.out.println(oid);       
                                      System.out.println(response);                 }else{       
                            System.out.println("get   error:"+response.getErrorStatusText());       
              }       
        }else{       
                        System.out.println("get         response       error");       
                    }     
  }       catch   (IOException     e)     {       
                                  //       TODO     Auto-generated     catch       block       
                            e.printStackTrace();       
      }           }       
}       运行结果是：   
request   UDP:GET[requestID=0,   errorStatus=Success(0),   errorIndex=0,   VBS[1.3.6.1.2.1.1.1   =   Null]]   
get   response   error   为什么得到的response是null呢？是不是还需要安装什么agent?       请大家帮忙指点指点