Java Websocket Client without a Browser

Question

I am working on a project that requires real-time interaction between users. I want to have a HTML5 web client (simple enough) and also a local client (preferably Java) with both being able to connect to the server. I have done some research and have not found a conclusive answer to whether or not the local client can connect to the server without a browser.

Question: Is there any way to connect from a local Java client to a websocket server without a browse? I have seen some browser wrappers in other languages that might make this possible. If not, I am open to suggestions.

Thanks.

Answer 1

Netty is a good choice for such task, it's a high performance network application framework and it supports SSL elegantly, here is netty websocket client example from netty github:

public final class WebSocketClient {

static final String URL = System.getProperty("url", "ws://127.0.0.1:8080/websocket");

public static void main(String[] args) throws Exception {
    URI uri = new URI(URL);
    String scheme = uri.getScheme() == null? "ws" : uri.getScheme();
    final String host = uri.getHost() == null? "127.0.0.1" : uri.getHost();
    final int port;
    if (uri.getPort() == -1) {
        if ("ws".equalsIgnoreCase(scheme)) {
            port = 80;
        } else if ("wss".equalsIgnoreCase(scheme)) {
            port = 443;
        } else {
            port = -1;
        }
    } else {
        port = uri.getPort();
    }

    if (!"ws".equalsIgnoreCase(scheme) && !"wss".equalsIgnoreCase(scheme)) {
        System.err.println("Only WS(S) is supported.");
        return;
    }

    final boolean ssl = "wss".equalsIgnoreCase(scheme);
    final SslContext sslCtx;
    if (ssl) {
        sslCtx = SslContextBuilder.forClient()
            .trustManager(InsecureTrustManagerFactory.INSTANCE).build();
    } else {
        sslCtx = null;
    }

    EventLoopGroup group = new NioEventLoopGroup();
    try {
        // Connect with V13 (RFC 6455 aka HyBi-17). You can change it to V08 or V00.
        // If you change it to V00, ping is not supported and remember to change
        // HttpResponseDecoder to WebSocketHttpResponseDecoder in the pipeline.
        final WebSocketClientHandler handler =
                new WebSocketClientHandler(
                        WebSocketClientHandshakerFactory.newHandshaker(
                                uri, WebSocketVersion.V13, null, true, new DefaultHttpHeaders()));

        Bootstrap b = new Bootstrap();
        b.group(group)
         .channel(NioSocketChannel.class)
         .handler(new ChannelInitializer<SocketChannel>() {
             @Override
             protected void initChannel(SocketChannel ch) {
                 ChannelPipeline p = ch.pipeline();
                 if (sslCtx != null) {
                     p.addLast(sslCtx.newHandler(ch.alloc(), host, port));
                 }
                 p.addLast(
                         new HttpClientCodec(),
                         new HttpObjectAggregator(8192),
                         WebSocketClientCompressionHandler.INSTANCE,
                         handler);
             }
         });

        Channel ch = b.connect(uri.getHost(), port).sync().channel();
        handler.handshakeFuture().sync();

        BufferedReader console = new BufferedReader(new InputStreamReader(System.in));
        while (true) {
            String msg = console.readLine();
            if (msg == null) {
                break;
            } else if ("bye".equals(msg.toLowerCase())) {
                ch.writeAndFlush(new CloseWebSocketFrame());
                ch.closeFuture().sync();
                break;
            } else if ("ping".equals(msg.toLowerCase())) {
                WebSocketFrame frame = new PingWebSocketFrame(Unpooled.wrappedBuffer(new byte[] { 8, 1, 8, 1 }));
                ch.writeAndFlush(frame);
            } else {
                WebSocketFrame frame = new TextWebSocketFrame(msg);
                ch.writeAndFlush(frame);
            }
        }
    } finally {
        group.shutdownGracefully();
    }
}
}

public class WebSocketClientHandler extends SimpleChannelInboundHandler<Object> {

private final WebSocketClientHandshaker handshaker;
private ChannelPromise handshakeFuture;

public WebSocketClientHandler(WebSocketClientHandshaker handshaker) {
    this.handshaker = handshaker;
}

public ChannelFuture handshakeFuture() {
    return handshakeFuture;
}

@Override
public void handlerAdded(ChannelHandlerContext ctx) {
    handshakeFuture = ctx.newPromise();
}

@Override
public void channelActive(ChannelHandlerContext ctx) {
    handshaker.handshake(ctx.channel());
}

@Override
public void channelInactive(ChannelHandlerContext ctx) {
    System.out.println("WebSocket Client disconnected!");
}

@Override
public void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
    Channel ch = ctx.channel();
    if (!handshaker.isHandshakeComplete()) {
        handshaker.finishHandshake(ch, (FullHttpResponse) msg);
        System.out.println("WebSocket Client connected!");
        handshakeFuture.setSuccess();
        return;
    }

    if (msg instanceof FullHttpResponse) {
        FullHttpResponse response = (FullHttpResponse) msg;
        throw new IllegalStateException(
                "Unexpected FullHttpResponse (getStatus=" + response.status() +
                        ", content=" + response.content().toString(CharsetUtil.UTF_8) + ')');
    }

    WebSocketFrame frame = (WebSocketFrame) msg;
    if (frame instanceof TextWebSocketFrame) {
        TextWebSocketFrame textFrame = (TextWebSocketFrame) frame;
        System.out.println("WebSocket Client received message: " + textFrame.text());
    } else if (frame instanceof PongWebSocketFrame) {
        System.out.println("WebSocket Client received pong");
    } else if (frame instanceof CloseWebSocketFrame) {
        System.out.println("WebSocket Client received closing");
        ch.close();
    }
}

@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
    cause.printStackTrace();
    if (!handshakeFuture.isDone()) {
        handshakeFuture.setFailure(cause);
    }
    ctx.close();
}
}

Answer 2

You might also consider using JSR 356 - Java API for WebSocket. It is part of Java EE 7, but client can be run from plain Java SE without any issues. There are multiple implementations available right now and following will work in all of them:

programmatic API:

    final WebSocketContainer webSocketContainer = ContainerProvider.getWebSocketContainer();

    Session session = webSocketContainer.connectToServer(new Endpoint() {
        @Override
        public void onOpen(Session session, EndpointConfig config) {
            // session.addMessageHandler( ... );
        }
    }, URI.create("ws://some.uri"));

annotated API:

public static void main(String[] args) throws IOException, DeploymentException {
    final WebSocketContainer webSocketContainer = ContainerProvider.getWebSocketContainer();
    webSocketContainer.connectToServer(MyEndpoint.class, URI.create("ws://some.uri"));
}

@ClientEndpoint
public static class MyEndpoint {

    // text
    @OnMessage
    void onMessage(Session session, String message) {
        // ...
    }

    // binary
    @OnMessage
    void onMessage(Session session, ByteBuffer message) {
        // ...
    }

    // @OnClose, @OnOpen, @OnError
}

please see linked page for further details (full specification).

There are various implementations out here, basically every Java container has one. I am working on Glassfish/WebLogic implementation and its called Tyrus, feel free to try it out (we provide easy to use all in one bundle, see http://search.maven.org/...).