CODEWITHSUNDEEP
javamysql
Edoardo Guani
Edoardo Guani

Reputation: 23

Why can't I connect java to MySql , (connection error)?

I'm trying to connect MySql and Java, but I get this error from this code.

Code:


public class ConnessioneMySql {
    public static void main(String[] args) throws SQLException {
        Connection cn;
        Statement st;
        ResultSet rs;
        String sql;


        cn = DriverManager.getConnection("jdbc:mysql://localhost:3306/TelegramBot", "root", "password");


        sql = "SELECT * FROM Utente;";

        try {
            st = cn.createStatement();
            rs = st.executeQuery(sql);
            while (rs.next() == true) {
                System.out.println(rs.getString("IdUtente") +
                        "\t" + rs.getString("CAPITALE")
                        + "\t" + rs.getString("N_Inviti")
                        + "\t" + rs.getString("Guadagno")
                        + "\t" + rs.getString("DataUltimoAggiornamento"));
            }
        } catch (SQLException e) {
            System.out.println("errore:" + e.getMessage());
        } 
        cn.close(); 
    }
}

Error:

Exception in thread "main" com.mysql.cj.jdbc.exceptions.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 com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
    at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:836)
    at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:456)
    at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:246)
    at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:198)
    at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677)
    at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:228)
    at ConnessioneMySql.main(ConnessioneMySql.java:11)
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: 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 java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:481)
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
    at com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167)
    at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:89)
    at com.mysql.cj.NativeSession.connect(NativeSession.java:144)
    at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:956)
    at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:826)
    ... 6 more
Caused by: java.net.ConnectException: Connection refused: connect
    at java.base/sun.nio.ch.Net.connect0(Native Method)
    at java.base/sun.nio.ch.Net.connect(Net.java:503)
    at java.base/sun.nio.ch.Net.connect(Net.java:492)
    at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:588)
    at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:333)
    at java.base/java.net.Socket.connect(Socket.java:648)
    at com.mysql.cj.protocol.StandardSocketFactory.connect(StandardSocketFactory.java:155)
    at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:63)
    ... 9 more

Process finished with exit code 1

I dont actualy use a localhost, but a vps i just replace the real addres with "localhost".

MySql is running.

MySql version:8.0.21

mysql-connector-java version:8.0.22

Maybe is a problem of firewall or something...

Upvotes: 0

Views: 1384

Answers (2)

Edoardo Guani
Edoardo Guani

Reputation: 23

At the end i discovered that it was a problem of firewalls, and i resolved it in my vps.

Upvotes: 1

Kennedy
Kennedy

Reputation: 37

  1. Make sure you have a database named "TelegramBot".

2.Make sure the MySql service is running. you can do this by checking "services" in the task manager

  1. Modify the code: Replace this:

cn = DriverManager.getConnection("jdbc:mysql://localhost:3306/TelegramBot", "root", "password");

with this:

String url = "jdbc:mysql://localhost:3306/TelegramBot?useUnicode=true&useJDBCCompliantTimeZoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC";

    cn = DriverManager.getConnection(url, "root", "password");

Upvotes: 0

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