Chat application in Java over the Internet | ConnectException (connection timed out)

I'm trying to develop a basic chat application. I've written the required codes for both the server and the client, and the application works perfectly fine over the LAN. When I tried to make it work over the Internet, however, I got stuck. I learned that I need to make a port-forwarding in the server machine, and I did that. I forwarded the port 6000 and canyouseeme.org gave a successful message. So, the port is surely open and no firewall is blocking it. However, the client code cannot connect to it.

The server code opens a ServerSocket as follows (their definitions are made previously):

InetAddress IP = InetAddress.getLocalHost();
welcomeSocket = new ServerSocket(6000, 10, IP);
connectionSocket = welcomeSocket.accept();

And the client code tries to connect to it mainly using the following code:

clientSocket = new Socket("xx.xxx.xxx.xx", 6000);

where xx.xxx.xxx.xx is the server machine's IP address (not the local one with 192.168.x.x).

Is this a Java issue? I am asking because the port 6000 is apparently open and canyouseeme.org can successfully connect to it, but my client fails to do so. Why such a thing happens? Any help would be appreciated (For further info, please read the comments below).

The error message is below:

java.net.ConnectException: Connection timed out: connect
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
    at java.net.Socket.connect(Socket.java:519)
    at java.net.Socket.connect(Socket.java:469)
    at java.net.Socket.<init>(Socket.java:366)
    at java.net.Socket.<init>(Socket.java:180)
    at ChatPanel$ConnectButtonListener.actionPerformed(ChatPanel.java:206)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
    at java.awt.Component.processMouseEvent(Component.java:6038)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
    at java.awt.Component.processEvent(Component.java:5803)
    at java.awt.Container.processEvent(Container.java:2058)
    at java.awt.Component.dispatchEventImpl(Component.java:4410)
    at java.awt.Container.dispatchEventImpl(Container.java:2116)
    at java.awt.Component.dispatchEvent(Component.java:4240)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
    at java.awt.Container.dispatchEventImpl(Container.java:2102)
    at java.awt.Window.dispatchEventImpl(Window.java:2429)
    at java.awt.Component.dispatchEvent(Component.java:4240)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

On the client you should use

clientSocket = new Socket(InetAddress.getByAddress(addr), port);

where addr is the public address of the server and port is the server bound to.