为什么错了？显示第13行错误

import java.sql.*;
public class jdbcDemo {
   public static void main(String[] args) {
      try {
         Class.forName ( "com.mysql.jdbc.Driver" );
        String url = "jdbc:mysql://localhost:3306/user";
         String username = "root";
         String password = "root";
         Connection connection = DriverManager.getConnection (url, username, password );
         Statement statement = connection.createStatement ();
         String sql = "select * from jdbctest;";
         ResultSet resultSet = statement.executeQuery ( sql );
         while (resultSet.next ()) {
            int id = resultSet.getInt ( "uid" );
            String user = resultSet.getString ( "username" );
            String pass = resultSet.getString ( "password" );
            System.out.println ( id + " :" + user + ":" + pass + ";" );
         }
      } catch (SQLException e) {
         e.printStackTrace ();
      } catch (ClassNotFoundException e) {
         e.printStackTrace ();
      }
   }
}

---错误提示：

F:\jdk\bin\java.exe "-javaagent:F:\IDEA\IntelliJ IDEA 2018.1.6\lib\idea_rt.jar=64938:F:\IDEA\IntelliJ IDEA 2018.1.6\bin" -Dfile.encoding=UTF-8 -classpath F:\jdk\jre\lib\charsets.jar;F:\jdk\jre\lib\deploy.jar;F:\jdk\jre\lib\ext\access-bridge-64.jar;F:\jdk\jre\lib\ext\cldrdata.jar;F:\jdk\jre\lib\ext\dnsns.jar;F:\jdk\jre\lib\ext\jaccess.jar;F:\jdk\jre\lib\ext\jfxrt.jar;F:\jdk\jre\lib\ext\localedata.jar;F:\jdk\jre\lib\ext\nashorn.jar;F:\jdk\jre\lib\ext\sunec.jar;F:\jdk\jre\lib\ext\sunjce_provider.jar;F:\jdk\jre\lib\ext\sunmscapi.jar;F:\jdk\jre\lib\ext\sunpkcs11.jar;F:\jdk\jre\lib\ext\zipfs.jar;F:\jdk\jre\lib\javaws.jar;F:\jdk\jre\lib\jce.jar;F:\jdk\jre\lib\jfr.jar;F:\jdk\jre\lib\jfxswt.jar;F:\jdk\jre\lib\jsse.jar;F:\jdk\jre\lib\management-agent.jar;F:\jdk\jre\lib\plugin.jar;F:\jdk\jre\lib\resources.jar;F:\jdk\jre\lib\rt.jar;C:\Users\Gyc\Desktop\JDBC\out\production\JDBC;C:\Users\Gyc\Desktop\JDBC\lib\junit-4.11.jar;C:\Users\Gyc\Desktop\JDBC\lib\mysql-connector-java-5.1.7-bin.jar jdbcDemo
java.sql.SQLException: Unknown initial character set index '255' received from server. Initial client character set can be forced via the 'characterEncoding' property.
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
	at com.mysql.jdbc.ConnectionImpl.configureClientCharacterSet(ConnectionImpl.java:1689)
	at com.mysql.jdbc.ConnectionImpl.initializePropsFromServer(ConnectionImpl.java:3444)
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2062)
	at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:723)
	at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)
	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:406)
	at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
	at java.sql.DriverManager.getConnection(DriverManager.java:664)
	at java.sql.DriverManager.getConnection(DriverManager.java:247)
	at jdbcDemo.main(jdbcDemo.java:13)

Process finished with exit code 0