这个问题在这里已经有答案了：

com.mysql.jdbc.exceptions.jdbc4.communicationsexception:通信链路故障（39个答案）
两年前关门了。
我正在创建一个应用程序，我需要连接到一个远程mysql数据库。我使用jsch通过ssh连接。我可以通过jsch连接，但是当我尝试连接到我的数据库时，我总是会出错。

public void connectSSH() {
    int lport = 5656;
    String rhost = "host"; //not actual host
    String host = "host"; //not actual host
    int rport = 3306;
    String user = "user"; //not actual user
    String password = "*********";
    String dbuserName = "user"; //not actual user
    String dbpassword = "********";
    String driverName = "com.mysql.jdbc.Driver";
    String url = "jdbc:mysql://127.0.0.1:" + rport + "?user=" + dbuserName + "&password=" + dbpassword + "&useSSL=true";
    Connection conn = null;
    Session session = null;
    try {
        //Set StrictHostKeyChecking property to no to avoid UnknownHostKey issue
        java.util.Properties config = new java.util.Properties();
        config.put("StrictHostKeyChecking", "no");
        JSch jsch = new JSch();
        session = jsch.getSession(user, host, 22);
        session.setPassword(password);
        session.setConfig(config);
        session.connect();
        System.out.println("Connected");
        int assinged_port = session.setPortForwardingL(lport, rhost, rport);
        System.out.println("localhost:" + assinged_port + " -> " + rhost + ":" + rport);
        System.out.println("Port Forwarded");

        //mysql database connectivity
        Class.forName(driverName).newInstance();
        conn = DriverManager.getConnection(url);
        System.out.println("Database connection established");
        System.out.println("DONE");
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            if (conn != null && !conn.isClosed()) {
                System.out.println("Closing Database Connection");
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        if (session != null && session.isConnected()) {
            System.out.println("Closing SSH Connection");
            session.disconnect();
        }
    }
}

输出：

Connected
localhost:5656 -> rhost:3306
Port Forwarded
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago.The driver has not received any packets from the server.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:342)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2188)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2221)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2016)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:776)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:386)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:270)
at com.ej.ozyazgan.classes.SqlHelper.connectSSH(SqlHelper.java:176)
at com.ej.ozyazgan.classes.MainController.initialize(MainController.java:52)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2566)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3214)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
at com.ej.ozyazgan.classes.Main.start(Main.java:13)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$161(LauncherImpl.java:863)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$174(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$172(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$173(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:301)
... 43 more
Closing SSH Connection
The url cannot be null