Com.mysql.jdbc.exceptions.jdbc4.communicationsexception: communications link failure

Question

Problem :

I want my database to talk to my Java programs.

I am getting following error message.

Exception in thread "main" 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:48)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:36)

at java.lang.reflect.Constructor.newInstance(Constructor.java:612)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:518)

at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:2233)

at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:3351)

at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:999)

at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:56)

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:40)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:30)

at java.lang.reflect.Constructor.newInstance(Constructor.java:600)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:512)

at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:410)

at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:300)

at java.sql.DriverManager.getConnection(DriverManager.java:600)

at java.sql.DriverManager.getConnection(DriverManager.java:310)

at SqlTest.main(SqlTest.java:33)

Caused by: 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.

Can somebody give me the quick and easy fix for my issue?

Contents of my test file as below:

import com.mysql.jdbc.*;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

public class JdbcSqlTest {

public static void main(String [] args) throws Exception {

 // Class.forName( "com.mysql.jdbc.Driver" ); // do this in init

        // // edit the jdbc url

        Connection connect = DriverManager.getConnection(

            "jdbc:mysql://localhost:3310/projects?user=user1&password=123");

        // Statement stat = connect.createStatement();

        // ResultSet result = stat.executeQuery( "select * from table" );

        System.out.println("Connected?");

    }

}

Answer 1

This is best and easiest solution for you,

Connection connect = DriverManager.getConnection( 

"jdbc:mysql://localhost:3310/DBname", "root", "root"); 

Connection connect = DriverManager.getConnection( 

"jdbc:mysql://192.100.0.000:3310/DBname", "root", "root");

I just Replaced the Localhost with your IP address.

Answer 2

If you get an SQLException: Connection refused or connection timed out or a MySQL specific CommunicationException:

Communication links failure then it means that the DB is not reachable at all.

Reasons:

This error can have one or more reasons that are described as;

• IP address or hostname in JDBC URL is wrong.
• The hostname in JDBC is not recognized by the local DNS server.
• Port number is missing or wrong in JDBC URL.
• The database server is down.
• The database server does not accept the TCP/IP connections.
• The database server has run out of connections.
• Something is between Java and Database has blocked the connection like a firewall or proxy.

Solution:

To solve one or the other error, just follow the following procedure;

• Verify and test them with ping.
• Refresh DNS or use an IP address in JDBC URL instead.
• Verify it based on my.cnf of MYSQL database.
• Start the database.
• Verify if MySQL is started without using the –skip-networking option.
• Restart the database and fix your code accordingly that it closes the connection finally.
• Disable the firewall or configure the firewall to forward the port.

Replacement of localhost:

This error can also be solved by the replacement of the localhost to the actual database server IP address.

Replace from;

Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/DBname", "root", "root");

To;

Connection con = DriverManager.getConnection("jdbc:mysql://192.100.0.000:3306/DBname", "root", "root");