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Overview A while back I had to create an implementation of a Server and Client communications system for a personal script of mine. My implementation was shit. Here's a much better one. It's still a bit unrefined so if you have an improvement, post it and I'll consider it for revision. The implementation for a lot of the class events is abstract, meaning the user determines what he wants to do when those events fire. Both Server and Client feature a heartbeat system, where after a certain time interval, the Client will send some info to the Server to let it know it's still alive. Likewise every time interval the Server does the same, but for each Client Connection it has saved. Servers and Clients both always have threads open which wait for Objects to be read. When an Object is read, an event will be fired as mentioned below. If the Object read is a Request (covered later on), then it will be displayed through a separate designated event. Implementations of the following events are not mandatory. If you don't want to handle certain events, simply create a constructor for the Server/Client, but leave the blocks for the unused event blank. Server events public abstract void onConnectionGain(Connection connection); Fired whenever a Client successfully connects to the Server, providing you the Connection that was just established. public abstract void onConnectionLoss(Connection connection, Exception e); Fired whenever a Connection is dropped, except when the Server closes a Connection manually when its shutdown() method is called. The Exception describes the circumstances that lead to the Connection being dropped. public abstract void onWrite(Serializable object); Fired whenever an Object is written to every Connection in the Server's list of current Connections. public abstract void onWrite(Serializable object, Connection connection); Same as above, but fires once for each Connection in the Server's Connection list at the time of writing the Object. public abstract void onRead(Object object, Connection connection); Fires whenever an Object is received on the Server's end from a Client Connection. Does not fire when a Request is received, the following event handles those cases. public abstract void onRequest(Request request, Connection connection); Fires whenever a Request is received on the Server's end from a Client. This class should handle implementation of how exactly you want to handle Requests. Requests will be covered in detail later on in the post. public abstract void onShutdown(); Fires at the end of Server#shutdown(). Client events public abstract void onConnectionGain(); Fired when the Client successfully established a Connection to the Server. public abstract void onConnectionLoss(Exception e); Fired when the Client's Connection to the Server drops. The Exception describes the circumstances that lead to the Connection being dropped. public abstract void onRead(Object object); Fires when the Client receives an Object from the Server. This again does not fire when a Request is received, that is handled by the event below. public abstract void onRequest(Request request); Fires when a Request is received on the Client's end, from the Server. public abstract void onShutdown(); Fires at the end of Client#shutdown(). Functionality The primary function of a Server/Client implementation like this is to facilitate communication between the Client and Server. Communication can happen across multiple scripts and even multiple computers. They must all be on the same network, however. Reading more than one Object at a time is unsupported (would corrupt underlying streams), and the same for writing. You can, however, read and write at the same time. To set this up, the user must specify which port the Server will be set up on, and then create Clients that attempt to connect to that port. You can do this through the constructors like so: Note the implementations of each event in the example above do not need to contain any actual code, they just need to have their headers. Clients will automatically attempt to re-connect to the Server with their designated port number. If the Server connection is lost while a Client is still online, it will fire a onConnectionLoss(...) event and wait 1 second before reconnecting. If a Client connection drops while the Server is still online, the Server will simply fire onConnectionLoss(...) and do nothing special. When a Connection is dropped, either Server or Client, you won't know about it until you try to read/write to it. This is why both Server and Client implement a "heartbeat" system. Every time interval (0.5 seconds) the Server sends a null Object to each Client, and each Client does the same for its Server. This simply ensures a minimum read/write frequency between the Server and Client so that dropped connections can be handled properly. On read/write from a disconnected Connection, an error will be thrown, which will properly remove the Connection from the Server's list and fire onConnectionLoss(...). Writing Communication between Server and Client is two-way, meaning the Server can send Objects and Requests to any of its Connections and the Client can do the same to its designated Server. A Server can have as many Connections as your heap space allows, however a Client can only have 1 Server Connection. Reads happen automatically via their own threads, however writes must be handled directly by the user. Anything you want to write must be Serializable, otherwise you'll get an Exception. Here's how the write methods work: Server public void write(Serializable object) Simply writes the given Serializable to every Connection in the Server's current Connection list. Fires onWrite(Serializable object); public void write(Serializable object, Connection connection) Writes the Serializable to only the specified Connection. Fires onWrite(Serializable object, Connection connection); Client public void write(Serializable object) Writes the given object Fires onWrite(Serializable object); When writing Requests, if the Request is unfulfilled (see section below), it will appear in the recipient's onRequest(...) event. Requests Finally I'll get to Requests, which is one of the main things I built this system to handle. A Request is a specialized Object, sent to a recipient, with the expectation for it to be returned, but with some modification. A Client may want to send a Request containing a Point with coordinates (-1, -1), expecting it to be returned with different coordinates. Here's an example of what that might look like: Simply extend Request<T> where T is the type of Object you want to be able to modify and implement Serializable so that the Request can actually be sent. When you initialize the Request<Point>, it will contain a Point (or otherwise specified type) variable called "target" which will be null until the Request is fulfilled. To fulfill the Request, simply call Request#fulfill(Object ... args) with the proper argument parameters (in this case 2 ints). The Request will automatically process the parameters in the way specified by your abstract implementation of Request#execute(Object ... args), and update the "target" from null to whatever the result actually is. If Request#execute(...) throws an Exception at any point, the Request will simply be processed as unfulfilled and ignored, even if it is written back to the sender. Here's what Request fulfillment looks like: To send Requests, simply call the Client or Server's fulfill(...) method. It will write the specified Request to the target(s), wait for it to be returned as fulfilled, and then return it. If it doesn't receive the Request within a designated time frame, it'll throw a RequestTimeoutException. Requests use System.nanoTime() as an identifier to ensure the originally sent Request is returned at the end of the method call. This is a failsafe to ensure you don't accidentally return a different Request to the one that was originally sent out. Classes That's it. Here are the classes: