Communications link failure com mysql jdbc exceptions jdbc4 CommunicationsException

Question

I'm working on getting my database to talk to my Java programs.

Can someone give me a quick and dirty sample program using the JDBC?

Contents of the test file:

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 SqlTest {

    public static void main(String [] args) throws Exception {
        // Class.forName( "com.mysql.jdbc.Driver" ); // do this in init
        // // edit the jdbc url 
        Connection conn = DriverManager.getConnection( 
            "jdbc:mysql://localhost:3306/projects?user=user1&password=123");
        // Statement st = conn.createStatement();
        // ResultSet rs = st.executeQuery( "select * from table" );

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

I'm getting a rather stupendous error:

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:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1122)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2260)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:787)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:49)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:357)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
    at java.sql.DriverManager.getConnection(DriverManager.java:582)
    at java.sql.DriverManager.getConnection(DriverManager.java:207)
    at SqlTest.main(SqlTest.java:22)
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.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method).......

Answer 1

I might be barking up the wrong tree here, but your exception seems to indicate your MySQL server isn't available.

Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failureThe last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. at...

What happens if you try (from the terminal)

mysql -u username -p

You will be prompted for the password associated with the username. After you give the correct password does the mysql client connect?

You may have to start MySQL from the Preferences if not. You can also set it to run at startup.

If you want to know more about SQL, it is recommended that you go for the SQL Course.

Answer 2

I catch this exception when Java out of heap.
If I try to put in RAM many data items - first I catch "Communications link failure" and next "OutOfMemoryError".

I logged it and I decrease memory consumption (delete 1/2 data) and all ok.

Hope this helps.

Answer 3

This com.mysql.jdbc.exceptions.jdbc4.CommunicationsException exception occurs if your database connection is idle for long time. 

Comments

How to solve this? Coz we are using connection pooling C30 but still having this issue.

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Hi @Subhrajit!

Can you tell me which database you are using and whether you are able to access it from the terminal?

Answer 4

I will suggest to go with database pooling. As idle connection returns true on connection.isClosed(); but if we try to execute statement then it will fire this exception so 

Answer 5

Instead of using localhost:[Apache Port], use your MySQL port.

Below is the default MySQL Port for MAMP server.

String url = "jdbc:mysql://localhost:8889/db_name";

Connection conn = DriverManager.getConnection(url, dbUsername, dbPassword);

I was having the same problem and I did this and it worked fine.

Answer 6

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

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

Replacement of Localhost to your IP address. This can be the best solution and easy one too.

Answer 7

I got the same error because I was trying to run my program without starting mysql server.

After starting the mysql server, everything went right.

Answer 8

I got this error because i didn't start my server before running this program.

Answer 9

When you are using WAMP or XAMP server to install mysql database. Then you have to explicitly start mysql sever other wise it will show com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure while connecting with database

Answer 10

It could be a simple jar problem. may be you are using a old mysql-connector-java-XXX-bin.jarwhich is not supported by your current mysql version. I used mysql-connector-java-5.1.18-bin.jaras i am using mysql 5.5 and this problem is resolved for me.

Answer 11

you mysql server instance is not running .

Answer 12

I had the same problem.then i did the following steps:

   1.My mysql connector jar file was a old verion whereas the mysql server is latest. so check the versions and download accordingly.

   2.Close both your IDE and mysql server and restart it after some time. Restarting solves many problems.

Now run the program.

Hope this helps!!!

Answer 13

So, you have a

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
java.net.ConnectException: Connection refused

I'm quoting from this answer which also contains a step-by-step MySQL+JDBC tutorial:

If you get an SQLException: Connection refused or Connection timed out or a MySQL specific CommunicationsException: Communications link failure, then it means that the DB isn't reachable at all. This can have one or more of the following causes:

1. IP address or hostname in JDBC URL is wrong.
2. Hostname in JDBC URL is not recognized by local DNS server.
3. Port number is missing or wrong in JDBC URL.
4. DB server is down.
5. DB server doesn't accept TCP/IP connections.
6. DB server has run out of connections.
7. Something in between Java and DB is blocking connections, e.g. a firewall or proxy.
    

To solve the one or the other, follow the following advices:

1. Verify and test them with ping.
2. Refresh DNS or use IP address in JDBC URL instead.
3. Verify it based on my.cnf of MySQL DB.
4. Start the DB.
5. Verify if mysqld is started without the --skip-networking option.
6. Restart the DB and fix your code accordingly that it closes connections in finally.
7. Disable firewall and/or configure firewall/proxy to allow/forward the port.

Answer 14

• Your exception seems to indicate that your MySQL server is not available.

         Exception in thread “main” com.mysql.exceptions.jdbc4.

         CommunicationsException:

         Communication link failure. The last packet sent successfully to the server was 0 milliseconds ago.                            

           No packet has been received by the driver from the server.   

I also got this error once because I didn't start my server before running this program.

I ran my program without starting the MySQL server.

So, I did cross-checking and after starting the MySQL server, everything was fine.

You can also try another approach where you can do replacement of Localhost to your IP address:

• Now, trying from the terminal:

Mysql -u username -p

• You will be asked for the password associated with the username. Does the MySQL client connect after providing the correct password?
• You might have to start MySQL from the preferences. If not, you can also set it to run at the startup.