مشکل اتصال به دیتابیس



 String connection = "jdbc:mysql://%s:%s/%s?useUnicode=true&characterEncoding=UTF-8";

        conn = DriverManager.getConnection(String.format(connecti  on, "x.x.x.x", "3306", "schoolController"), "user", "passwd");

        System.out.println("OK");

        st = conn.createStatement();

یه هفته هست هس با کد مشکل دارم اصلا به دیتابیس متصل نمیشه.
خطا:



Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsExce  ption: 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.newInsta  nce0(Native Method)

    at sun.reflect.NativeConstructorAccessorImpl.newInsta  nce(NativeConstructorAccessorImpl.java:62)

    at sun.reflect.DelegatingConstructorAccessorImpl.newI  nstance(DelegatingConstructorAccessorImpl.java:45)

    at java.lang.reflect.Constructor.newInstance(Construc  tor.java:423)

    at com.mysql.jdbc.Util.handleNewInstance(Util.java:41  1)

    at com.mysql.jdbc.SQLError.createCommunicationsExcept  ion(SQLError.java:1117)

    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:355)

    at com.mysql.jdbc.ConnectionImpl.coreConnect(Connecti  onImpl.java:2461)

    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(Co  nnectionImpl.java:2498)

    at com.mysql.jdbc.ConnectionImpl.createNewIO(Connecti  onImpl.java:2283)

    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImp  l.java:822)

    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connect  ion.java:47)

    at sun.reflect.NativeConstructorAccessorImpl.newInsta  nce0(Native Method)

    at sun.reflect.NativeConstructorAccessorImpl.newInsta  nce(NativeConstructorAccessorImpl.java:62)

    at sun.reflect.DelegatingConstructorAccessorImpl.newI  nstance(DelegatingConstructorAccessorImpl.java:45)

    at java.lang.reflect.Constructor.newInstance(Construc  tor.java:423)

    at com.mysql.jdbc.Util.handleNewInstance(Util.java:41  1)

    at com.mysql.jdbc.ConnectionImpl.getInstance(Connecti  onImpl.java:404)

    at com.mysql.jdbc.NonRegisteringDriver.connect(NonReg  isteringDriver.java:317)

    at java.sql.DriverManager.getConnection(DriverManager  .java:664)

    at java.sql.DriverManager.getConnection(DriverManager  .java:247)

    at schoolcontroller.tools.DataBase.mysql.DataAccess.c  onnect(DataAccess.java:45)

    at schoolcontroller.tools.DataBase.mysql.DataAccess.m  ain(DataAccess.java:40)

هم اسم دیتابیس هم ای پی سرور و هم یوزرنیم و پسورد درسته و به راحتی با نرم افزار Mysql Workbench میتونم به سرور متصل بشم.

نسخه MySQL Server :



5.7.19-0ubuntu0.16.04.1