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

In my case, the solution was to add the expected TLS protocol to the connection string like this:

jdbc:mysql://localhost:3306/database_name?enabledTLSProtocols=TLSv1.2 

For testing/development purposes (not recommended for production) you can also try:

jdbc:mysql://localhost:3306/database_name?useSSL=false&allowPublicKeyRetrieval=true 

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"); 

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.

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.

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!

Add this useSSL=false&allowPublicKeyRetrieval=true

jdbc:mysql://localhost:3306/cloudapp?useSSL=false&allowPublicKeyRetrieval=true

https://youtu.be/ray3YvnIohM

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); 

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.

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.

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.

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" ); 

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.

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

bind-address = 0.0.0.0 

Restart mysql deamon and mysql services.

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 

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

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.

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.

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.

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

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.

dbhost=jdbc:mysql://172.18.23.100:3306/yourdatabase?useUnicode=yes&characterEncoding=UTF-8&useSSL=false user=root password=Password#321 con = DriverManager.getConnection(dbhost, user, password); 

if mysql version 8 or higher user updated connector

In my case, turn out to be that the version of mysql-connector-java was different. I just changed mysql jdbc to maria jbdc

Old jdbc driver

<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java --> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.21</version> </dependency> 

New Jdbc driver

<!-- https://mvnrepository.com/artifact/org.mariadb.jdbc/mariadb-java-client --> <dependency> <groupId>org.mariadb.jdbc</groupId> <artifactId>mariadb-java-client</artifactId> <version>2.6.2</version> </dependency> 

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&password=123"); 

Regards.

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.

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.

Sample jdbc connection class file. simply call the getConnection method when you want to get a connection. include related mysql-connector.jar

import java.sql.Connection; import java.sql.DriverManager; public class DBConnection { public Connection getConnection() { Connection con = null; String dbhost; String user; String password; // get properties dbhost="jdbc:mysql://localhost:3306/cardmaildb"; user="root"; password="123"; System.out.println("S=======db Connecting======"); try { Class.forName("com.mysql.jdbc.Driver"); con = DriverManager.getConnection(dbhost, user, password); //if you are facing with SSl issue please try this //con = DriverManager.getConnection("jdbc:mysql://192.168.23.100:3306/cardmaildb?useUnicode=yes&characterEncoding=UTF-8&useSSL=false",user, password); } catch (Exception e) { System.err.println("error in connection"); e.printStackTrace(); } System.out.println("E=======db Connecting======"); return con; } public static void main(String[] args) { new DBConnection().getConnection(); } } 

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&useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC' jdbc.user='theNewUser' 

Open file /etc/mysql/my.cnf: change below parameter from

`bind-address = 127.0.0.1

to

bind-address = 0.0.0.0 #this allows all systems to connect

Run below command in mysql for specific IP Address->

grant all privileges on dbname.* to dbusername@'192.168.0.3' IDENTIFIED BY 'dbpassword'; 

If you want to give access to all IP Address, run below command:

grant all privileges on dbname.* to dbusername@'%' IDENTIFIED BY 'dbpassword'; 

I have the same connection error: The problem I have is I used MySQL 8.0.15 but the Java Connector is 5.x.x.

Below is how I fixed it. 1. download the 8.0.15. from Maven repository: https://search.maven.org/search?q=g:mysql%20AND%20a:mysql-connector-java

2. In the Eclipse IDE, select the "Referenced Libraries" in Explorer Right Mouse Button > Build Path > Configure Build Path a. remove the "mysql-connector-5.x.jar" b. Click "Add External JARs..." and select mysql-connector-java-8.0.15.jar.

Re-run it, the problem went away.