Telnet Client part 2 - using Apache net implementation...

I have shown Telnet client using socket programming which is my own logic.But Apache has already done this for us in their Net package which is freely available to download.So we can use that org.apache.commons.net.telnet.TelnetClient class for using telnet connection.

Its a very simple class.You can download its source and can figure out what they have done. Though i will show simple usage for it.

TelnetClient tc = new TelnetClient();
tc.connect("localhost", 23);

Then you can register a listener thread to get response from the telnet connection shown above. For full examples, check out java2s

Its nothing new, but a good implementation what we understood so far.
If you want totally command prompt like session for telnet, then you must wait for response from execution of the given command.Then only the next command will be sent over, as we do in DOS/Terminal.So for that we must have a logic which check the input stream and receives response.

Telnet client with java...

Telnet is very important utiliy we use.We can call remote server commands and use different services running on perticular port.Mostly telnet server runs on 23,but can be differed .

Through java, if we want to make remote connection over some port then we have two different ways.

1. Use windows/linux telnet command line utility (which is same on both win and linux... :).)

OR

2. Use socket programming using java.net package.

In first way, we need to get hands on the process.We can achieve that using

Process p = Runtime.getRuntime().exec(<system command or exe path>)

But i don't think this should be used for telnet like communication,because telnet requires continuous session running on remote server and executing you commands.Sometimes it can be so that after executing several commands,you need to rollback so you can cancle all the commands.so its a continuous and sequential process most of the times.The Process class used can be out of our hands anytime if the executable crashes or if anything bad happen(Mostly..the exe crash...).

So, we have another,'Socket' way here, which connects to perticular host on given port number and try to open TCP connection with it.If the host is listening on port and connection accepted,then we can send our commands to the host.(I know, i know, that we all know sockets since our starting graduation days :) ,but let me tell guys... ).

There are two ways to make a telnet client using Sockets.
1.Make it CLI based,means which accepts every input from Command Line Interface entered by user.
2.Make it automated,which takes command list from some file or database,generates a script or list of commands and run it whole on host.

First one is quite easy,i think you all might have done that :).Just let me tell you little what to do...

1.CLI based Telnet...

Socket soc = new Socket(host,port);
DataInputStream din=new DataInputStream(soc.getInputStream());
PrintWriter dout = new PrintWriter(soc.getOutputStream(),true);
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

See,we have taken InputStream of socket and made a PrintWriter on the OutputStreamof it to send commands.Also we have taken BufferedReader for user inputs from CL.

...
....

do
{
char[] buffer = new char[8192];
int mark = bReader.read(buffer);
StringBuffer sb = null;
for(int i=0;i<buffer.length;i++){
char c = buffer[i];
if(c!='\0'){ //To avoid null characters printed...
if(sb == null){
sb = new StringBuffer(buffer.length);
}
sb.append(c);
}
}
System.out.print((sb!=null)?sb.toString():"-- No Response --");
Command=br.readLine(); //takes commands from CL by user...
if(!Command.equals("quit"))
{
dout.println(Command);
}
}while(!Command.equals("quit")); //exit the loop if user sends 'quit'...
...

This gives you same telnet as you got in your OS, so i think its simple but good to know :)


2.Automated Telnet...

It will be almost same,except we will have a ArrayList/Array of commands in hand before we create Socket.And then change the loop onto the list to execute all the commands one after another...

int j=-1;
String[] commands = new String[5];

...
....

do
{
j++;
char[] buffer = new char[8192];
int mark = bReader.read(buffer);
StringBuffer sb = null;
for(int i=0;i<buffer.length;i++){
char c = buffer[i];
if(c!='\0'){//To avoid null characters printed...
if(sb == null){
sb = new StringBuffer(buffer.length);
}
sb.append(c);
}
}
System.out.print((sb!=null)?sb.toString():"-- No Response --");
Command = commands[j];
if(Command==null || Command.length()<0)
break;
dout.println(Command+"\n");
}while(j<commands.length);
...

So this will executes all commands in commands Array of String.


So folks,this ends our telnet socket :).Same like this we can make client or scripts for FTP automation.It helps in real time situation when you need to make some jobs for backup,export/import files on remote host etc...Waiting for you responses...

Snmp4J - Java library for SNMP Communication...

We all know that if we need to use more on socket programming in java then we must use native code in c++.SNMP (Simple network Management Protocol) is used for communication with the network devices.Any network device can be queried using SNMP request.Snmp4j is the library which provides you implementation to make SNMP requests.

We can query any device (Switch,PC etc...) if it has a SNMP agent running,which will handle our SNMP request and respond with the proper data.This library made it so easy for us without looking into much details of SNMP.

In basic,SNMP is used for getting information (GET requests),but sometimes it can be used to set values in the device (SET requests).Assume that every device has a list of pre-defined variables in it,which are called OID(Object IDs).These OIDs will have a specific structure (which is called MIB file,which seems like a tree structured as in registry).

OID looks like 1.3.6.1.4.1.318.1.1.1.12.3.2.1.3.1, which has a special meaning.It has a description(name) and an associated value in it.When you query particular OID (i.e 1.3.6.1....),it will give its associated value.You can set its value also (if its allowed ;)).OIDs also have communities(Public,Private etc...) which shows permissions.Mostly public community is allowed to be viewed by SNMP requests.

See the example below how to make a SNMP request,

import org.snmp4j.*;

...
...

OctetString communityName = new OctetString("public");

String ipAddressUrl = strIpAddress+"/"+161; //161 is used for SNMP Agent...

Address targetAddress = new UdpAddress(ipAddressUrl);

TransportMapping transport = new DefaultUdpTransportMapping();

Snmp snmp = new Snmp(transport);

snmp.listen();

CommunityTarget target = new CommunityTarget();

target.setAddress(targetAddress);
target.setRetries(3);
target.setTimeout(500);

PDU pdu = new PDU();
pdu.setType(PDU.GET);

OID oid = new OID("1.3.6.1.2.1.1.");
VariableBinding vb = new VariableBinding(oid);

pdu.add(vb);
...
...

snmp.send(pdu, target);

So the last line, snmp.send(pdu, target), will return the SNMP4j Response having the value for OID we set in the PDU.This is just the example of how to get any data from OID.We can set the values using SET PDU.

Batch insert/update DB - Use XML as you data...

Today we have many strange requirements because of latest developments in the IT market. We are having tons of data to be inserted in databases or files etc.Mainly for DB operation, we can use batch insert/update, which calls DB for multiple rows of params.

This is not an excellent thing, but i think you should take care of this.Just think that if you are having 100 rows to be inserted in one table, and you make batch update call from you java code.How much time and resources it will take?We just can't answer this question.Yeah, we can't but we have different solution here.

Instead of making batch params data, you make and XML data using XSLT transformation or Castor mapping.We will see what these both things mean later. Today every Database server supports XML parameters as an input to Stored procedure/Function.You can pass your XML to the SP, and then handle the XML traversal logic inside the SP.You are done!

You just need to,

1.Create the XML data for Input param.
2.Pass the XML,execute the SP.
3.SP will handle the XML data and do the processing fetching the data from XML(Using Xpath traversal)
4.SP also can return resultset data as an XML content, which you can again transform map to Object.


XML Transformation: is done by javax.xml.Transform package, which takes one XML as input,Used XSLT file to transform input XML to XML format as defined by the XSLT.


Castor Mapping:is done by third party open source jar, which maps Object to XML and XML to object.So you can directly get XML/Object using this.

Remote Method call - EJB/HTTPClient/Web Service?

This is not a new thing i am talking about,but i have used this for first time. Until now i have been used to EJB for remote method invocations. I use it for some bussiness logic which is on another distributed server. And i am not ashamed of telling that i have not used Web services :(.

This was a need in my project to call a method of another application which can be on same machine or another. First i thought i need to call a EJB and its all mess because of heavy loads for a simple method call. But when i saw the implementation, i got confused how i will cuse it! But my senior told me to check using HTTPClient from apache commons.

Its very simple to call a method on servlet using HTTPClient. Check the code below. We will just use PostMethod class for parameters to be passed and execute the request. So as per the parameters,the servlet will do its work.

PostMethod postMethod = new PostMethod("http://some.blah.com");
postMethod.setParameter("some_id", "1");
postMethod.setParameter("param1", "any data");
postMethod.setParameter("param2", "any data");
...
int status = httpClient.executeMethod(postMethod); //status will be your response...

Its so simple. But though its not a call which returns something. I mean you cna see i am just passign some information to some method to invoke some processing which is independent and i don't need its response.