java – com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The Question :

242 people think this question is useful

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?

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)
    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.MysqlIO.<init>(MysqlIO.java:344)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2181)
    ... 12 more
Caused by: java.net.ConnectException: Connection refused
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:432)
    at java.net.Socket.connect(Socket.java:529)
    at java.net.Socket.connect(Socket.java:478)
    at java.net.Socket.<init>(Socket.java:375)
    at java.net.Socket.<init>(Socket.java:218)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:256)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:293)
    ... 13 more

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&amp;password=123");
        // Statement st = conn.createStatement();
        // ResultSet rs = st.executeQuery( "select * from table" );

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

The Question Comments :
  • I was a stupid. MySQL server was not started 🙁 It was successful after starting it.

The Answer 1

268 people think this answer is useful

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 a 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.

See also:

The Answer 2

10 people think this answer is useful

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.

The Answer 3

10 people think this answer is useful

In my case, I needed to do a replacement of Localhost to the actual database server IP address

Instead of

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

I needed

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

The Answer 4

8 people think this answer is useful

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

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

The Answer 5

6 people think this answer is useful

I’ve been having the same problem for hours. I’m using MAMP Server

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);

The Answer 6

5 people think this answer is useful

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.

The Answer 7

5 people think this answer is useful

In my case, turn out to be that the version of mysql-connector-java was too old.

In my demo, I somehow use mysql-connector-java like this:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.9</version>
</dependency>

But in the develop environment, I use this:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.31</version>
</dependency>

And my MySQL version was 5.1.48(yes, it is old, just for mimic the product version). So I met the same error.

Since the reason is found, the solution is found, too. Match the version!

The Answer 8

4 people think this answer is useful

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.

The Answer 9

4 people think this answer is useful

Earlier answers are appropriate . But , I would also like to point towards a more generic issue.

I faced similar issue and the reason was a network restriction of my company.

Same connection was getting successful when I was in any other network.

The Answer 10

4 people think this answer is useful

Please update your IP address in /etc/mysql/my.cnf file

bind-address  = 0.0.0.0

Restart mysql deamon and mysql services.

The Answer 11

3 people think this answer is useful

Download MySQL-JDBC-Type-4-Treiber (i.g. ‘mysql-connector-java-5.1.11-bin.jar’ from ‘mysql-connector-java-5.1.11.zip’) at Mysql.

You need to inculde the driver jar during compile- and runtime in your classpath.

Class.forName( "com.mysql.jdbc.Driver" ); // do this in init
// edit the jdbc url 
Connection conn = DriverManager.getConnection( "jdbc:mysql://MyDbComputerNameOrIP:3306/myDatabaseName", username, password );
Statement st = conn.createStatement();
ResultSet rs = st.executeQuery( "select * from table" );

The Answer 12

3 people think this answer is useful

i solved this problem in a easy way, that worked for me. i had the seme problem “com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure”. In my db.properties file i had this : url:jdbc:mysql://localhost:90/myDB, only removed the port url , resulting in this manner url:jdbc:mysql://localhost/myDB and that worked for me.

The Answer 13

3 people think this answer is useful

This error may also happen if Java tries to connect to MySQL over SSL, but something goes wrong. (In my case, I was configuring Payara Server 5.193.1 connection pools to MySQL.)

Some people suggested setting useSSL=false. However, since Connector/J version 8.0.13, that setting is deprecated. Here’s an excerpt from MySQL Connector/J 8.0 Configuration Properties:

sslMode

By default, network connections are SSL encrypted; this property permits secure connections to be turned off, or a different levels of security to be chosen. The following values are allowed: DISABLED – Establish unencrypted connections; PREFERRED – (default) Establish encrypted connections if the server enabled them, otherwise fall back to unencrypted connections; REQUIRED – Establish secure connections if the server enabled them, fail otherwise; VERIFY_CA – Like REQUIRED but additionally verify the server TLS certificate against the configured Certificate Authority (CA) certificates; VERIFY_IDENTITY – Like VERIFY_CA, but additionally verify that the server certificate matches the host to which the connection is attempted.

This property replaced the deprecated legacy properties useSSL, requireSSL, and verifyServerCertificate, which are still accepted but translated into a value for sslMode if sslMode is not explicitly set: useSSL=false is translated to sslMode=DISABLED; {"useSSL=true", "requireSSL=false", "verifyServerCertificate=false"} is translated to sslMode=PREFERRED; {"useSSL=true", "requireSSL=true", "verifyServerCertificate=false"} is translated to sslMode=REQUIRED; {"useSSL=true" AND "verifyServerCertificate=true"} is translated to sslMode=VERIFY_CA. There is no equivalent legacy settings for sslMode=VERIFY_IDENTITY. Note that, for ALL server versions, the default setting of sslMode is PREFERRED, and it is equivalent to the legacy settings of useSSL=true, requireSSL=false, and verifyServerCertificate=false, which are different from their default settings for Connector/J 8.0.12 and earlier in some situations. Applications that continue to use the legacy properties and rely on their old default settings should be reviewed.

The legacy properties are ignored if sslMode is set explicitly. If none of sslMode or useSSL is set explicitly, the default setting of sslMode=PREFERRED applies.

Default: PREFERRED

Since version: 8.0.13

So, in my case, setting sslMode=DISABLED was all I needed to resolve the issue. This was on a test machine. But for production, the secure solution would be properly configuring the Java client and MySQL server to use SSL.


Notice that by disabling SSL, you might also have to set allowPublicKeyRetrieval=true. (Again, not a wise decision from security standpoint). Further information is provided in MySQL ConnectionString Options:

AllowPublicKeyRetrieval

If the user account uses sha256_password authentication, the password must be protected during transmission; TLS is the preferred mechanism for this, but if it is not available then RSA public key encryption will be used. To specify the server’s RSA public key, use the ServerRSAPublicKeyFile connection string setting, or set AllowPublicKeyRetrieval=True to allow the client to automatically request the public key from the server. Note that AllowPublicKeyRetrieval=True could allow a malicious proxy to perform a MITM attack to get the plaintext password, so it is False by default and must be explicitly enabled.

The Answer 14

3 people think this answer is useful

My same problem is solved by the following steps:

  1. Go to my.cnf

    vi /etc/mysql/my.cnf
    
    
  2. Modify its bind-address

    "bind-address = 0.0.0.0"
    
    
  3. Restart MySQL

    sudo /etc/init.d/mysql restart
    
    

The Answer 15

2 people think this answer is useful

If 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

The Answer 16

2 people think this answer is useful

Thats happened to me when I changed the mysql port from 3306 to 3307 in my.ini and the php.ini files but after changing the ports (3307->3306) back it worked fine again.

The Answer 17

2 people think this answer is useful

If you changed your port, you get this kind of error “com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure” Please check your port number

The Answer 18

2 people think this answer is useful

Try to change localhost to 127.0.0.1.

The localhost would be resolved to ::1. And MySQL cannot be connected via IPv6 by default.

And here is the output of telnet localhost 3306:

$ telnet localhost 3306
Trying ::1...

And there is no response from MySQL server.

Of course, please make sure your MySQL server is running.

The Answer 19

1 people think this answer is useful

Just experienced this.

Got to make it work by: (this can be placed in the static block intializer)

static{ // would have to be surrounded by try catch
    Class.forName("com.mysql.jdbc.Driver");   // this will load the class Driver
}

Also by obtaining the connection through:

conn = DriverManager.getConnection(DBURL,<username>,<password>);

instead of specifying the login parameters

  Connection conn = DriverManager.getConnection( "jdbc:mysql://localhost:3306/projects?user=user1&amp;password=123");

Regards.

The Answer 20

1 people think this answer is useful
dbhost=jdbc:mysql://172.18.23.100:3306/yourdatabase?useUnicode=yes&amp;characterEncoding=UTF-8&amp;useSSL=false
user=root
password=Password#321

con = DriverManager.getConnection(dbhost, user, password);

if mysql version 8 or higher user updated connector

The Answer 21

1 people think this answer is useful

For Remote Call to Mysql

  1. Add remote user to Mysql from for exemple IP=remoteIP :

    mysql -u xxxx -p //local coonection to mysql
    mysql> GRANT ALL PRIVILEGES ON *.* TO 'theNewUser'@'remoteIP' IDENTIFIED BY 'passWord';
    //Query OK, 0 rows affected (xx sec)
    mysql> FLUSH PRIVILEGES;
    //Query OK, 0 rows affected
    
    
  2. Allow remote access to Mysql (by default all externall call is not allowed):

    Edit 
    /etc/mysql/mysql.conf.d/mysqld.cnf    or    /etc/mysql/my.cnf
    Change line:  bind-address = 127.0.0.1   to
                  bind-address = 0.0.0.0
    Restart Mysql: /etc/init.d/mysql restart
    
    
  3. For The latest version of JDBC Driver, the JDBC :

    jdbc.url='jdbc:mysql://remoteIP:3306/yourDbInstance?autoReconnect=true&amp;amp;useUnicode=true&amp;amp;useJDBCCompliantTimezoneShift=true&amp;amp;useLegacyDatetimeCode=false&amp;amp;serverTimezone=UTC'
    jdbc.user='theNewUser'
    
    

The Answer 22

0 people think this answer is useful

I had the same problem, and here’s how it was fixed:

  1. My .jsp was calling attributes that I had not yet defined in the servlet.
  2. I had two column names that I was passing into an object through ResultSet (getString("columnName")) that didn’t match the column names in my database.

I’m not exactly sure which one fixed the problem, but it worked. Also, be sure that you create a new Statement and ResultSet for each table query.

The Answer 23

0 people think this answer is useful

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

The Answer 24

0 people think this answer is useful

Maybe you did not start your Mysql and Apache Server. After I started Apache server and Mysql from XAMPP Control Panel, connection was successfully established.

Good luck!

The Answer 25

0 people think this answer is useful

What solved for me is doing 2 thing: 1. create new user other than root with some password using following connads:

CREATE USER 'newuser'@'localhost' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON *.* TO 'newuser'@'localhost';
FLUSH PRIVILEGES;

2. comment IP address line on mysqld.conf

then connect with new username and password. it should work.

The Answer 26

0 people think this answer is useful

It was trying to connect to an older version of MySQL (‘version’, ‘5.1.73’ ); when you use a newer driver version you get an error that tells you to use the “com.mysql.cj.jdbc.Driver or even that you don’t have to especify which one you use:

Loading class com.mysql.jdbc.Driver'. This is deprecated. The new driver class iscom.mysql.cj.jdbc.Driver’. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.

I changed the declaration to use 5.1.38 version of the mysql-connector-java and, in the code, I kept the com.mysql.jdbc.Driver.

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.38</version>
</dependency>

All started when I saw the Ankit Jain’s answer

The Answer 27

0 people think this answer is useful

My firewall was blocking post 3307 which my MySQL listening on. So I changed port from 3307 to 3306.Then I can successfully connect to a database.

The Answer 28

0 people think this answer is useful

In my MacBook i have solvet this error only when reinstall the new version of eclipse EE and remove local servers like xamp mysql or mamp but use only one of them …

The Answer 29

0 people think this answer is useful

In my case I had to establish an ssh tunnel to the remote database and all the settings were correct and testing the connection with PhpStorm were also successful. And also the schema was loaded, but not the data. Instead I got:

[08S01] 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.

No of the suggestions above worked. For any reason I tried to solve the problem by simply restarting PhpStorm and voila it worked!

The Answer 30

0 people think this answer is useful

I was receiving multiple errors such as:

  • CommunicationsException: Communications link failure
  • java.lang.NullPointerException: Attempt to invoke interface method 'java.sql.Statement java.sql.Connection.createStatement()' on a null object reference at.

I had to add:

  • In AndroidManifest.xml include <uses-permission android:name="android.permission.INTERNET"/> just after the opening manifest tag.

  • Add the JDBC driver into your Gradle (or Maven) dependencies.

Tags:, ,

Add a Comment