3 Connecting to server

This chapter tells how to use GNU WebSocket4J in a client application.

Naming convention

Throughout this chapter WebSocket will refer to websocket4j.client.WebSocket class.

General idea

WebSocket class works similar to java.net.Socket — you have to create an instance providing information where it should connect to and you get back a socket that is ready to use (see Using an established socket).

Creating a WebSocket instance

WebSocket has two constructors, first one takes a String, Integer and String, second one takes an additional Integer. First String is the host name of the server you want to connect to, first Integer is port on which the server listens for incoming connections. Second String is URI that should be requested when connecting — just as HTTP servers, WebSocket servers can handle multiple kinds of connections over one port.

For example new WebSocket("localhost", 5432, "/echo") would connect to localhost on port 5432 and request /echo URI. In JavaScript API you'd use ws://localhost:5432/echo URI to connect to the same server.

Fourth, optional, argument of the constructor is timeout in milliseconds, if the opening handshake takes more time than this, an IOException will be thrown.

Closing the socket

Just like the server socket, client sockets have close() : void method that ends the connection. Also you can use isClosed() : Boolean method to check if the socket is already closed.