Question mark (mysql) _ MySQL

When connecting to the database in Java, Chinese characters become question marks (mysql)

Package Login; import java. SQL. connection; import java. SQL. driverManager; public class GetConn {public Connection conn = null; public Connection getConnection () {try {Class. forName ("com. mysql. jdbc. driver "); String url =" jdbc: mysql: // localhost: 3306/select_courses "+ "? UseUnicode = true & characterEncoding = utf8 "; // determines the character set String user =" root "; String passWord =" "; conn = DriverManager. getConnection (url, user, passWord); if (conn! = Null) {System. out. println ("database link succeeded") ;}} catch (Exception e) {e. printStackTrace () ;}return conn ;}}