How to Java SNMP Programming

Question

Hello all,
I'm new to SNMP and I am trying to create an SNMP agent using JAVA to monitor my applications, I'm looking for tutorials on SNMP java programming and code samples, any suggestions/guiding/advising is welcomed.
Regards,
Hussam Galal

Answer 1

I'm not new to SNMP, and I wouldn't attempt to write an agent in Java. You need access to low level information in the system, which Java is unable to get. A subagent is an easier task, you could look at using the the Agent X subagent protocol. Many agents support this. There is an AgentX implementation written in Java.
Here's a self contained class that logs traps received from a Linksys router. It knows the format of the trap and doesn't use the MIB, it only deals with the bits of BER that it needs. To go further you would need to write a MIB compiler and a BER interpreter.
import java.io.*;
import java.net.*;
import java.text.*;
import java.util.*;
public class LinksysTrap extends Thread
     DatagramSocket dgSocket = null;
     Thread recvThread = null;
     boolean running = false;
     String filefmt;
     String enterprise;
     String fname="";
     File outfile=null;
     FileWriter outWrite = null;
     SimpleDateFormat stf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
     SimpleDateFormat sdf;
     // the packet
     byte [] data = new byte[32768];
     int ofs, end;               // values for packet
     // current token
     int tlen, ttype, tofs;     // values for current token
     // trap fields
     int ver;
     String comm;
     String ent;
     String ipa;
     int gtt, stt, tt;
     String oid;
     String val;
     LinksysTrap(String e, String p)
          enterprise = e;
          filefmt = p;
          sdf = new SimpleDateFormat(filefmt);
     private boolean startup(int port)
          try
               dgSocket = new DatagramSocket(port);
               System.out.println("bound to port="+port);
               if(openFile(new Date()))
                    running = true;
                    this.start();
               else dgSocket.close();
          catch(IOException e){e.printStackTrace(); running = false;}
          return running;
     public void run()
          doRecv();
     private void doRecv()
          DatagramPacket pkt = new DatagramPacket(data,32768);
          while(running)
               try
                    dgSocket.receive(pkt);
                    end = pkt.getLength();
                    ofs = 0;
                    // System.out.println("packet received from:"+pkt.getAddress()+" port="+pkt.getPort()
                    // +" length="+end);
                    decode();
               catch(IOException e){e.printStackTrace(); running = false;}
          dgSocket.close();
     static public void main(String [] args)
          int port = 162;
          String ent ="1.3.6.14.1152.21.2.2.1";
          String filefmt="'traps'yyyyMM'.csv'";
          for(int i = 0; i<args.length; i++)
               String arg = args;
               if(arg.length() > 2)
                    char c0 = arg.charAt(0);
                    if(c0 == '-')
                         char c1 = arg.charAt(1);
                         arg = arg.substring(2);
                         switch(c1)
                              case 'p':          // port
                                   try{port = new Integer(arg).intValue();}
                                   catch(NumberFormatException exc){badCmd();}
                                   break;
                              case 'e':          // enterprise
                                   ent = arg;
                                   break;
                              case 'f':          // file prefix
                                   filefmt = arg;
                                   break;
                              default:
                                   badCmd();
                                   break;
                    }else badCmd();
               }else badCmd();
          LinksysTrap st = new LinksysTrap(ent, filefmt);
          if(!st.startup(port))System.exit(0);
     private static void badCmd()
          System.out.println("LinksysTrap -pport -eenterprise -ffilenameformat");
          System.out.println(" default -p162 -e1.3.6.14.1152.21.2.2.1 -f'traps'yyyyMM'.csv'");
          System.exit(0);
     private void decode()
          try
               getSeq(0x30);               // packet
               ver = getInt(0x02);          // version
               comm = getString();          // community
               getSeq(0xa4);               // trap pdu
               ent = getOID();               // enterprise
               if(! ent.equals(enterprise))
                    System.out.println("trap ignored from enterprise="+ent);
                    return;
               ipa = getIPA();               // ip address
               gtt = getInt(0x02);          // generic trap type
               stt = getInt(0x02);          // specific trap type
               tt = getInt(0x43);          // time up
               getSeq(0x30);               // varbind list
               getSeq(0x30);               // varbind
               oid = getOID();               // trap oid
               val = getString();          // trap value
          catch (IllegalArgumentException e)
               System.out.println("decoding error ofs="+ofs);
               display(data,0,end);
               e.printStackTrace();
          // System.out.println("trap received from enterprise="+ent);
          // System.out.println(" val="+val);
          record(val);
     private boolean openFile(Date dt)
          String fn = sdf.format(dt);
          if(!fn.equals(fname))
               if(outWrite != null)
                    try{outWrite.close();}      // close output writer
                    catch(IOException ce){ce.printStackTrace();}
                    finally {outWrite = null;}
               fname = fn;
               System.out.println("Opening file="+fname);
               outfile = new File(fname);
               try
                    outWrite = new FileWriter(fname,true);
                    if(0 == outfile.length())
                         outWrite.write("Timestamp,Direction,Source Address,Source Port,Destination Address,Destination Port\n");
                         outWrite.flush();
               catch (IOException e)
                    e.printStackTrace();
                    if(outWrite != null)
                         try{outWrite.close();}catch(Exception ce){}
                         outWrite= null;
          return outWrite != null;
     private void record(String val)
          Date dt = new Date();
          String ts = stf.format(dt);
          if(openFile(dt))
               String cs="";
               int i = 0;
               int j = 0;
               int z = val.length();
               if(val.charAt(0) == '@')i = 1;
               while(i < z)
                    if(' '==val.charAt(i))i++;
                    else
                         j = val.indexOf(' ',i);
                         if(j == -1)j = z;
                         cs += ","+val.substring(i,j);
                         i=j+1;
               if(cs.charAt(cs.length()-1) != '\n')cs+='\n';
               cs = ts+cs;
               System.out.println("cs="+cs);
               try
                    outWrite.write(cs);
                    outWrite.flush();
               catch(IOException we){we.printStackTrace();}
          else running = false;
     private void getSeq(int type)
     {getHeader(type);}
     // get an integer, this should deal with sign but doesn't yet ********* TBD
     private int getInt(int type)
          getHeader(type);
          int len = tlen;
          int r = 0;
          while(0 < len--)r = (256*r)+getUByte();
          return r;
     private String getString()
          getHeader(0x04);
          String s = new String(data, tofs, tlen);
          ofs+=tlen;
          return s;
     private String getOID()
          String s = "";
          getHeader(0x06);
          int i = getUByte();          // get first byte
          if(i >= 40){s = "1."; i -=40;}
          s += (i+".");
          int len = tlen-1;
          while(0 < len--)
               i = getUByte();
               s+=i;
               if(i>1)s+=".";
          return s;
     private String getIPA()
          String s = "";
          getHeader(0x40);
          int i;
          int len = tlen;
          while(0 < len--)
               i = getUByte();
               s+=i;
               if(i>1)s+=".";
          return s;
     // get token header
     private void getHeader(int type)
          int i,n;
          ttype = getUByte();     // token type
          if(type != 0 && type != ttype)
               System.out.println("ofs="+ofs+" ttype="+ttype);
               throw new IllegalArgumentException("invalid type");
          n = getUByte();
          if(n >= 128)
               i = n-128;
               n = 0;
               while(0 < i--)n=(n*256)+getUByte();
          tofs = ofs;
          tlen = n;
          // System.out.println("tofs="+tofs+ " tlen="+tlen+" ttype="+ttype);
     // get an unsigned byte from data
     private int getUByte()
          if(ofs >= end)throw new IllegalArgumentException("data too short");
          int b = data[ofs++];
          if(b < 0)b+=256;
          return b;
     private static final String HexValue[]={"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"};
     public static void display(byte[]ba, int ofs, int len)
          int dlen;
          String dstr;
          while(len>0)
               if(len < 16)
                    dlen = len;
                    char[] c48 = new char[48];
                    java.util.Arrays.fill(c48, ' ');
                    String fill48 = String.valueOf(c48);
                    dstr = fill48.substring(0,3*(16-dlen));
               else
                    dlen = 16;
                    dstr = "";
               dstr = tohex4(ofs)+": "+atohex(ba,ofs,dlen)+dstr+": "+atochar(ba,ofs,dlen);
               System.out.println(dstr);
               ofs+=dlen;
               len-=dlen;
     public static String atochar(byte[]ba, int ofs, int len)
          String s="";
     char ch;
     byte b;
     for(int i=ofs;i<(ofs+len);i++)
     b = ba[i];
     if(b < 32 || b >126)ch = '.';
               else ch = (char)b;
               s+=ch;
return s;
public static String atohex(byte[]ba, int ofs, int len)
String s="";
for(int i=ofs;i<(ofs+len);i++)
s += (tohex2(ba[i])+" ");
return s;
public static String tohex2(int b)
          int i = b;
          if(i<0)i+=256;
return HexValue[i/16]+HexValue[i%16];
public static String tohex4(int i)
          if(i<0)i+=32768;
          i = i%32768;
return tohex2(i/256)+tohex2(i%256);