mensajeCliente.addKeyListener(new KeyListener() {
            @Override
            public void keyTyped(KeyEvent e) {

            }
            @Override
            public void keyPressed(KeyEvent e) {
                if(e.getKeyCode()==KeyEvent.VK_ENTER){
                    enviarMensaje.doClick();
                }
            }
            @Override
            public void keyReleased(KeyEvent e) {
            }
        });