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Use Java to connect ethernet device

I had a board connect to the PC using LAN cable(RJ45). I need to write the Java code to connect the board and get some data from it. How can I do it?
Actually I got a code from C++, it used CAsyncSocket class to do it. The C++ code is like this:
CAsyncSocket.Create();
CAsyncSocket.connect(IP, PORT);
Now, I would like to convert it into Java. Actually, I'm not so familiar with Java. Can someone show the code to me?
Example: My board IP is 192.168.2.10 and PORT is 2000. How can I connect it using Java?

see here (for example):
Socket socket = new Socket("192.168.2.10", 2000);
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
System.out.println("Input: " + input.readLine());
socket.close();
http://docs.oracle.com/javase/7/docs/api/java/net/Socket.html

Check out the socket tutorial Lesson: All About Sockets:
URLs and URLConnections provide a relatively high-level mechanism for accessing resources on the Internet. Sometimes your programs require lower-level network communication, for example, when you want to write a client-server application.
See the [http://docs.oracle.com/javase/tutorial/networking/sockets/readingWriting.html](Reading from and Writing to a Socket) example:
Let's look at a simple example that illustrates how a program can establish a connection to a server program using the Socket class and then, how the client can send data to and receive data from the server through the socket.

Expanding my Java program to send a alert message to other computers

I've written a java intake program that send an PDF-formatted intake to a shared folder so that other people in the network can read it. However, there is not a way for the other people to know that an intake was sent unless someone tells them, so I want the program to send an alert message to the other computers telling them that an intake has been sent.
Now I've done some research into this and figured that TCP is the way to go since it's reliable. I also know that this is a one-to-many sending going on, so I assume that my Intake program will act as the server an the other computers will be the client, or should it be the other way around?
Now I assume that I have to create a client program that listens to the server and waits for it to send a message.
With that in mind, how do I:
Create a client program that listens for the message continuously until the program is closed. I assume that I'll be using "while (true)" and sleep. If so, how long do I put the program to sleep?
Make it as part of Windows service so that can load up when Windows start.
On the server end, how do I:
Send messages to more than one computer, since TCP is not capable of multicasting or broadcasting. I assume an array/vector will play a part here.
Oh, this is a one-way communication. The client doesn't have to respond back to the server.

First of all, UDP is quite reliable (in fact, as reliable as the IP protocol itself). TCP simply ensures that the data was received which involved quite a lot of magic in the back end. Unless you absolutely need to be sure that other machines got the message, you could do it with UDP. Mind that I'm not saying “Don't use TCP”, I just want to make it straight that you should take UDP into consideration as well.
Anyway, yes, you can create a simple listening program. Here is an example of a client in Java that reads messages from the server. It overrides the run method of a Thread class:
public void run() {
try {
String messageFromServer = reader.readLine();
while (messageFromServer != null) {
// Do things with messageFromServer here
// processor.processFromServer(messageFromServer);
messageFromServer = reader.readLine(); // Blocks the loop, waits for message
}
}
catch (IOException e) {
// Handle your exception
}
}
Amongst other things, my thread was set up as such:
public CommunicationThread(String hostname, int port, int timeout) throws IOException, SocketTimeoutException {
InetSocketAddress address = new InetSocketAddress(hostname, port);
socket = new Socket();
socket.connect(address, 2000); // 2000ms time out
// You can use the writer to write messages back out to the server
writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
}
Now, regards to server-side you can do something as follows:
Write a program to allow clients to contact, given that they know your address.
Accept the connections, and store the sockets in a list.
When you need to send out a message, traverse the list and send the data to everyone on it.
You can start listening on your server with
this.socket = new ServerSocket(port);
You could (or even should(?)) make it threaded so that you can accept clients while serving others. You can accept new clients with:
socket.accept(); // Blocks, waiting for someone to connect, returns open socket
Feel free to pass that to a whole new class which can deal with BufferedWriter (and maybe even BufferedReader if you want to read from clients as well). That class is where you would implement things such as writeToClient(message)
Consider the situation where you have a ClientConnection class that has writeToClient(String s) method and (Server server, Socket socket) and initialized ArrayList conList.
Here is how you would follow:
In a separate thread in Server, accept connections with
ClientConnection con = new ClientConnection(this, socket.accept());
conList.add(con);
Then, when you want to write to clients:
for (ClientConnection c : conList) {
c.writeToClient("I'm sending you a message!");
}
I hope you get a vague idea of what you need to do. Read the Socket documentation, it's very useful. Also, as always with threaded applications, make sure you aren't doing things such as modifying a list while traversing it and avoid race conditions.
Good luck!

How can I modify this code to allow my client socket program to send a string to the server?

Hi ive written some code to connect to a server through the use of a socket. Id like to write some simple code that allows me to send a string to the server, im assuming this will involve input and output streams but I am new to this. Ive put the code I am working with below, any insights into the best way to accomplish this would be great.
import java.net.*;
import java.io.*;
public class SocketMarket
{
public static void main(String [] args)
{
String serverName = "XX.X.X.XXX";
int port = XXXX;
try
{
System.out.println("Connecting to " + serverName + " on port " + port);
Socket client = new Socket(serverName, port);
System.out.println("Connected to " + client.getRemoteSocketAddress());
}
catch(IOException e)
{
e.printStackTrace();
}
}
}
Thanks in advance

client.getOutputStream().write("Hello World".getBytes());
client.getOutputStream().flush();
The above is how you would send just a String, but you will probably want to build up some infrastructure around sending arbitrary text.
The general idea is that your server and client will communicate with each other using InputStream's and OutputStream's, which can be accessed from a Socket via getInputStream() and getOutputStream(), once the connection between them is made.
For your server to receive connections, you should be using a ServerSocket to accept() incoming connections.

Insight is here, the "really big index" for java.
http://docs.oracle.com/javase/tutorial/networking/sockets/readingWriting.html

Yes, it involves OutputStreams. If you want to output Strings you could write raw bytes via the OutputStream you get from the connection but then you completely loose control over encoding. You need to learn about reader/writer/streams first, then networking via sockets is simple. You can find the relevant part of the Java tutorials here: http://docs.oracle.com/javase/tutorial/essential/io/ (you can ignore the NIO part completely for the beginning). After that you can learn about socket networking: http://docs.oracle.com/javase/tutorial/networking/sockets/index.html .

Server that receives a sequence of integers

I'm learning Sockets programming in Java. I'm trying to solve a problem that consists in:
Having a server that accepts a connection from one client on a
time. That part is solved.
Now I want the server to receive a sequence of integers in text
format that will finish when a end of file situation on the socket
reader stream is detected.
I'm trying to do this using DataInputStream and
DataOutputStream because thats the only thing that I know so far.
Can somebody help? I don't know how to the 2nd part of my problem.
I have the following code:
public class Exercise{
public static void main(String args[]) throws Exception {
ServerSocket server= new ServerSocket(6789);
while(true) {
try {
Socket aux= server.accept();
DataInputStream dis = new DataInputStream(aux.getInputStream());
DataOutputStream dos = new DataOutputStream(aux.getOutputStream());
while(dis != null) {
}
}
catch (EOFException e) {
out.println("The client finish execution!");
continue;
}
}
}
}

You need to define a protocol of data exchange. That's how all of the networking applications work. The client and server have to agree on a FORMAT and SEQUENCE of data that will be exchanged. The most basic thing you can do is send the following in sequence
START
1,2,3,4,5,6
STOP
The moment you receive START, you know the next input line is your sequence of integers which you can parse using your custom logic.
Once you receive STOP you know there wont be any more data and you stop and return the response/acknowledgement to the client.

Have a look at this page from the oracle website http://www.oracle.com/technetwork/java/socket-140484.html#server should have all the info you need to setup and receive String data from a socket connection.
To process a sequence of integers, would depend on the formatting, so you would want to make sure that they are seperated by space or some standard delimiter like white-space or comma (i.e. "1 2 3 4" or "1,2,3,4") and then use the StringTokenizer or a similar class to break up the String into individual integer Strings and then parse with Integer.parseInt();

Forwarding incoming TCP "Commands" to a function?

In Java, how would you set up a socket listener that listened to a socket for a series of bytes that represented a command and on recieving called a method which parsed the incoming data and invoked the appropriate command?
Clarification:
My issue is not with handling the commands (Which might also be error codes or responses to commands from the server) but with creating the socket and listening to it.
More Clarification:
What I want to do is mimic the following line of .Net (C#) code:
_stream.BeginRead(_data,0, _data.Length, new
AsyncCallback(this.StreamEventHandler), _stream);
Where:
_stream is a network stream created from a socket
_data is an array of Byte of length 9
this.StreamHandler is a delegate (function pointer) which get executed when data is read.
I am rewriting a library from C# into Java and the component I am currently writing passes commands to a server over TCPIP but also has to be able to bubble up events/responses to the layer above it.
In C# this seems to be trivial and it's looking less and less so in Java.

Starting from my other answer: The specific part you request is the one that goes into the section: "Magic goes here". It can be done in ohh so many ways, but one is:
final InputStream in = socket.getInputStream();
// This creates a new thread to service the request.
new Thread(new Runnable(){
public void run(){
byte[] retrievedData= new byte[ITEM_LENGTH];
in.read(retrievedData, 0, ITEM_LENGTH);
in.close();
// Here call your delegate or something to process the data
callSomethingWithTheData(retrievedData);
}
}).start();

Have a small main method which sets up the socket and listens for incoming connections. Pass each connection to a worker object (possibly in its own thread).
The worker object should have two APIs: The server and the client. The client API gets a connection and reads data from it, the server API takes a connection and writes data to it.
I like to keep these two in a single class because that makes it much more simple to keep the two in sync. Use a helper class to encode/decode the data for transmission, so you have single point to decide how to transmit integers, commands, options, etc.
If you want to go further, define a command class and write code to serialize that to a socket connection and read it from it. This way, you worker objects just need to declare which command class they handle and the server/client API gets even more simple (at the expense of the command class).

I would
put each command into a class of its own, where each class implements a specific interface (e.g. Command)
create a Map<String,Command> which contains a lookup table from each command string to an instance of the class that implements that command

This should help.
Lesson 1: Socket Communications

The TCP connection provides you with one InputStream and one OutputStream. You could just poll the InputStream continuously for the next command (and its inputs) on a dedicated thread. ByteBuffer.wrap(byte[] array) may be useful in interpreting the bytes as chars, ints, longs, etc. You could also pass objects around using serialization.

Any naive approach most likely will not scale well.
Consider using a REST-approach with a suitable small web-server. Jetty is usually a good choice.

To create an listen to a socket, in a very naive way:
mServerSocket = new ServerSocket(port);
listening = true;
while (listening) {
// This call blocks until a connection is made
Socket socket = serverSocket.accept();
OutputStream out = socket.getOutputStream();
InputStream in = socket.getInputStream();
// Here you do your magic, reading and writing what you need from the streams
// You would set listening to true if you have some command to close the server
// remotely
out.close();
in.close();
socket.close();
}
Normally it is a good idea to delegate the processing of the input stream to some other thread, so you can answer the next request. Otherwise, you will answer all requests serially.
You also need to define some kind of protocol of what bytes you expect on the input and output streams, but from your question it looks like you already have one.

You could create an enum with one member per command
interface Comamnd {
// whatever you expect all command to know to perform their function
void perform(Context context);
}
enum Commands implements Command{
ACTIONONE() {
void perform(Context context) {
System.out.println("Action One");
}
},
ACTIONTWO() {
void perform(Context context) {
System.out.println("Action Two");
}
}
}
// initialise
DataInputStream in = new DataInputStream(socket.getInputStream());
// in a loop
byte[] retrievedData= new byte[ITEM_LENGTH];
in.readFully(retrievedData);
String command = new String(retrievedData, 0);
Commands.valueOf(command).perform(context);