Thread.currentThread().join()

In this post, we shall implement a Trap Sender using SNMP4J. We may choose to use Apache MINA for sending Traps or can resort to using DatagramSocket class directly.

This shall be the logical flow of the implementation

• Get the encoded Trap Data
• Send the Trap 

The code snippet above shows a simple way of creating and encoding a Trap PDU. Essentially, we create an instance of PDU class and sets the type as Trap. This is important, else SNMP4J shall throw an exception. Thereafter, we can set the trap parameters. Here, we have hardcoded the parameters, there can be custom implementations that can take these from config files or from UI. After setting the parameters, we just call the encode function passing the Output stream and collect the byte array to be sent.

Sending part is even simpler     

The send code is preety straight forward. Here we have used Datagram Socket, we can use Apache MINA UDP Client implementation to send the trap as well.

References

• http://www.snmp4j.org/
• Implementing UDP Client using Apache MINA 

Will continues to post articles about MINA, to be updated,  Subscribe in a reader

Yes, we are going to implement a SNMP trap receiver in less than 30 minutes. If you have been following my post on Apache MINA, this would be a natural extension to it. In this article, we shall bring together all our components to build the system.

 Pre-requisites:

 Please read through these articles. You can find all these posts on Apache MINA

• What is Apache MINA
• Apache MINA based Server Application Architecture
• Implementing UDP Server using Apache MINA
• Implementing SNMP4J Decoder for Apache MINA

 To execute the code, you need following jars

• mina-core-2.0.0-M1.jar
• slf4j-api-1.5.0.jar
• slf4j-log4j12-1.5.0.jar
• log4j-1.2.15.jar
• SNMP4J.jar

 I am assuming that you have read my previous posts and jumping straight to the implementations. The high level architecture is explained in the post Apache MINA based Server Application Architecture

Architecture 

Let’s understand the flow here and see what all we need to do to process a trap

• Receive the trap over UDP
• Decode the Trap
• Dump the Trap

Lets see how each of the these maps to the code we have already written

It's a now simple to understand that we have reused all the components to create the Server. Let me not write too much, and jump straight to the code J

 The Server Code

The only change that we did to the UDP Server code was to add a Protocol Codec. At line 36, we added our custom ProtocolCodecFiler. The SNMPCodecFactory return the instance of our SNMP4J codec. There is not much code and this construct is fairly simple, and explained very well in MINA’s documentation. From the main method, we just need to call the method initialize() and our trap receiver starts.

References

• http://mina.apache.org/
• http://www.snmp4j.org/

In my last post we created a UDP client using Apache MINA. Lets turn the table and implement the Server side. Let's see how using Apache MINA reduces the effort to create a UDP Server.

Steps to create a UDP Server using java.net API's

1. Create a Socket and listen for incoming connection
2. Process each packet in a separate thread (I hate this, unfortunately need this to have high processing rate)
3. Parse and process the request and optionally send response (Lets omit this to keep things simple)

That's it

• Our protocol is carrying Strings in UDP packet
• We shall not do any transformation on the packets received. We shall just dump the content

The Handler

 

The Handler is in its basic form. Our only method of interest is messageReceived. Since we know that we are getting "String" message without any transformation, we could easily create a new string from the bytes received. A wonderful thing to note about this API is the parameter "message". This makes the API generic enough to cater to any kind of objects. If we had used a ProtocolCodec in the chain and had transformed the byte[] into a custom Object, we would have type-casted message to that object.

That's all in the handler.

 

The Server

Lets see the main Server code

 

 

The Server is even simpler than client

We create an instance of NioDatagramAcceptor and add our custom handler to it. We then bind to the port desired. Here I have made it bind to the default port, code can be customized to bind to any port desired.

So what does 31 does. There is wonderful description of this option at http://www.unixguide.net/network/socketfaq/4.5.shtml
The main function is pretty simple. The Server is ready. You can run it, using the Client from the post Implementing UDP Client using Apache MINA

References

• http://mina.apache.org/udp-tutorial.html

Its been a while that I wrote on Apache MINA. Please refer to my post collection on Apache MINA.

In this post, I have tried to capture briefly on how to implement a UDP Client using Apache MINA. We shall concentrate on keeping our scope limited to sending data over UDP. In Subsequent posts, we shall see how we can enhance this UDP Client to send SNMP Traps.

In brief, these are the steps we need to perform to send a UDP packet

1. Create a Datagram Socket
2. Create a Datagram Packet
3. Send the packet

1. Create a NioDatagramConnector instance
2. Add an IoHandler (we can use an IoHandlerAdapter, as for this example we don't need to use all the API's)
3. Connect the NioDatagramConnector
4. Get the session
5. Write the data onto the session

There is a slight difference in which the MINA API's work. The API's work asynchronously. A call to connect() on NioDatagramConnector, return a reference to ConnectFuture and the operation is kicked off in a new thread. Lets see how the Code looks like and see it in details.

 

 

Lets see the Code in detail now. We have maintained the Session at the class level, assuming that we may reuse the session for sending packets, if session is still active. At line 25, we check if the session is active or not. If inactive we initiate the connection. 

Line 28, creates an instance of NioDatagramConnector

Line 31, add an IoHandler to the NioDatagramConnector on Line 28. In MINA terminology, IoHandler contains the code where Business logic of an Application resides. In our case its a pure Adapter, with only log statements inside the functions.

Line 32, a call to connect(), returns an reference to ConnectFuture. The call, starts the connection operation, in a separate thread and returns to the caller. To cater to this asynchronous behaviour, we add an IoFutureListener, to returned ConnectFuture reference. Out there (Line 38-43), we just check if the connection is OK, we get the session from it. Line 39, signals that connection is connected and its safe to get the session for writing data.

The connect code is complete. Lets see how to send the data.

The send function is pretty simple. We just create an IoBuffer and call write on the session. We have called connect() on Line 59, just to ensure that the connection is alive. If it isn't, it shall create a connection and return a session back.

NOTE: This code is in its very simple form. There can be various mechanism to handle Session (based on destination etc). Also, please be aware of the asynchronous behaviour of the NioDatagramConnector connect() API. If the connection is not complete in time, you might see a null pointer at Line 67 . But this is usually the case. For production code, it is advisable to ensure that session is never null.

That's it, out UDP client is ready. To create an SNMP Trap sender, we just need to pass Trap byte array to send() and we are done. Will try to post that article soon.

References

• http://mina.apache.org/udp-tutorial.html

Apache MINA is one of the best available NIO Frameworks for creating scalable Server applications in Java. Its fun to create applications using MINA. 

Lets have a look how the application architecture looks like

Lets briefly see what the Major components are

IO service - The API's at this level are responsible for performing actual IO operation over the network

IO Filters - Filters are the mechanism by which MINA lets a User plugin its code to manipulate the byte stream from the network. Filters are arranged in Filter chain and are called by MINA in the order in which they are present. Filters are mainly used for transforming byte stream into high level objects.

IO Handler - IO Handler is the heart of application logic. Here is where the whole application logic is concentrated.

MINA is JMX enabled, hence Filters can be dynamically added/removed from the Filter chain.

The framework comes with samples. Please feel free to try them out.