This discussion might give you some idea, which direction to go. On a
similar occasion, I took JNI and used a commercial C library for a
sepecial embedded OS; that was 2 years before though and nowadays those
libraries, mensioned in this forum discussion, look to be mature enough.
Let me know If you plan to implement it yourself for a special
deployment environment and need further help  on the ASN1(BER) encoding.

The original discussion:
forum.java.sun.com/thread.jspa?threadID=657620

and the standard specification (you sure already have that but for the
records)
http://www.ietf.org/rfc/rfc1157.txt

If fact, I have downloaded SNMP4j libs, but the problem is I cannot realize how to use them exactly! and what I exactly need to know to use them.

I mean, there is no clear-cut example  to use this libs in the net (or, I cannot find it so far) and as I am new in SNMP, I have no clue to write an SNMP "hello world" in java.

meanwhile, I saw the link already, There an example there but it is self-contained instead of using SNMP4j.

That looks like a pretty reasonable good library with tools to generate
the MIBs when required. What you should know first, is general
litreature of snmp.

Then you need your MIB extensions (if any) and your messages to play
with the stack. take the SmtpRequest console for start  before
integrating code into your programs. specially you need to know
what you want to do with what device, and to what extend.

Take the source of the SnmpRequest class for granted when generating
the messages for different pdutypes.

Look at the javadoc of the snmp  class to start your final integration. I
currently can not run a test against something as i don't have the
environment to test.

I uased iReasning snmp  (http://www.ireasoning.com/products.shtml) in a
project. It's commercial, but performance was unbelievably good! We had
a network of some 5000 nodes and had to collect snmp info every 5
minutes. The only tricky part was firing 5000 threads to collect those
data! Also, we used jRobin to draw nice monitoring graphs and such
based on the snmp data.