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com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
(51 answers)
Closed 6 years ago.
I'm trying to connect to the local MySQL server but I keep getting an error.
Here is the code.
public class Connect {
public static void main(String[] args) {
Connection conn = null;
try {
String userName = "myUsername";
String password = "myPassword";
String url = "jdbc:mysql://localhost:3306/myDatabaseName";
Class.forName("com.mysql.jdbc.Driver").newInstance();
conn = DriverManager.getConnection(url, userName, password);
System.out.println("Database connection established");
} catch (Exception e) {
System.err.println("Cannot connect to database server");
System.err.println(e.getMessage());
e.printStackTrace();
} finally {
if (conn != null) {
try {
conn.close();
System.out.println("Database Connection Terminated");
} catch (Exception e) {}
}
}
}
}
and the errors :
Cannot connect to database server
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.
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:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:344)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2333)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2370)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2154)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:792)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
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:411)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:381)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:305)
at java.sql.DriverManager.getConnection(DriverManager.java:582)
at java.sql.DriverManager.getConnection(DriverManager.java:185)
at Connect.main(Connect.java:16)
Caused by: java.net.ConnectException: Connection refused
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
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:257)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:294)
... 15 more
I've set the classpath, made sure my.cnf had the skip network option commented out.
java version is 1.2.0_26 (64 bit)
mysql 5.5.14
mysql connector 5.1.17
I made sure that the user had access to my database.
I have had the same problem in two of my programs. My error was this:
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.
I spent several days to solve this problem. I have tested many approaches that have been mentioned in different web sites, but non of them worked. Finally I changed my code and found out what was the problem. I'll try to tell you about different approaches and sum them up here.
While I was seeking the internet to find the solution for this error, I figured out that there are many solutions that worked for at least one person, but others say that it doesn't work for them! why there are many approaches to this error?
It seems this error can occur generally when there is a problem in connecting to the server. Maybe the problem is because of the wrong query string or too many connections to the database.
So I suggest you to try all the solutions one by one and don't give up!
Here are the solutions that I found on the internet and for each of them, there is at least on person who his problem has been solved with that solution.
Tip: For the solutions that you need to change the MySQL settings, you can refer to the following files:
Linux: /etc/mysql/my.cnf or /etc/my.cnf (depending on the Linux distribution and MySQL package used)
Windows: C:\**ProgramData**\MySQL\MySQL Server 5.6\my.ini (Notice it's ProgramData, not Program Files)
Here are the solutions:
changing bind-address attribute:
Uncomment bind-address attribute or change it to one of the following IPs:
bind-address="127.0.0.1"
or
bind-address="0.0.0.0"
commenting out "skip-networking"
If there is a skip-networking line in your MySQL config file, make it comment by adding # sign at the beginning of that line.
change "wait_timeout" and "interactive_timeout"
Add these lines to the MySQL config file:
[wait_timeout][1] = *number*
interactive_timeout = *number*
connect_timeout = *number*
Make sure Java isn't translating 'localhost' to [:::1] instead of [127.0.0.1]
Since MySQL recognizes 127.0.0.1 (IPv4) but not :::1 (IPv6)
This could be avoided by using one of two approaches:
In the connection string use 127.0.0.1 instead of localhost to avoid localhost being translated to :::1
Run java with the option -Djava.net.preferIPv4Stack=true to force java to use IPv4 instead of IPv6. On Linux, this could also be achieved by running (or placing it inside /etc/profile:
export _JAVA_OPTIONS="-Djava.net.preferIPv4Stack=true"
check Operating System proxy settings, firewalls and anti-virus programs
Make sure the Firewall, or Anti-virus software isn't blocking MySQL service.
Stop iptables temporarily on linux. If iptables are misconfigured they may allow tcp packets to be sent to mysql port, but block tcp packets from coming back on the same connection.
# Redhat enterprise and CentOS
systemctl stop iptables.service
# Other linux distros
service iptables stop
Stop anti-virus software on Windows.
change connection string
Check your query string. your connection string should be some thing like this:
dbName = "my_database";
dbUserName = "root";
dbPassword = "";
String connectionString = "jdbc:mysql://localhost/" + dbName + "?user=" + dbUserName + "&password=" + dbPassword + "&useUnicode=true&characterEncoding=UTF-8";
Make sure you don't have spaces in your string. All the connection string should be continues without any space characters.
Try to replace "localhost" with the loopback address 127.0.0.1.
Also try to add port number to your connection string, like:
String connectionString = "jdbc:mysql://localhost:3306/my_database?user=root&password=Pass&useUnicode=true&characterEncoding=UTF-8";
Usually default port for MySQL is 3306.
Don't forget to change username and password to the username and password of your MySQL server.
update your JDK driver library file
test different JDK and JREs (like JDK 6 and 7)
don't change max_allowed_packet
"max_allowed_packet" is a variable in MySQL config file that indicates the maximum packet size, not the maximum number of packets. So it will not help to solve this error.
change tomcat security
change TOMCAT6_SECURITY=yes to TOMCAT6_SECURITY=no
use validationQuery property
use validationQuery="select now()" to make sure each query has responses
AutoReconnect
Add this code to your connection string:
&autoReconnect=true&failOverReadOnly=false&maxReconnects=10
Although non of these solutions worked for me, I suggest you to try them. Because there are some people who solved their problem with following these steps.
But what solved my problem?
My problem was that I had many SELECTs on database. Each time I was creating a connection and then closing it. Although I was closing the connection every time, but the system faced with many connections and gave me that error. What I did was that I defined my connection variable as a public (or private) variable for whole class and initialized it in the constructor. Then every time I just used that connection. It solved my problem and also increased my speed dramatically.
#Conclusion#
There is no simple and unique way to solve this problem. I suggest you to think about your own situation and choose above solutions. If you take this error at the beginning of the program and you are not able to connect to the database at all, you might have problem in your connection string. But If you take this error after several successful interaction to the database, the problem might be with number of connections and you may think about changing "wait_timeout" and other MySQL settings or rewrite your code how that reduce number of connections.
If you are using MAMP PRO, the easy fix, which I really wish I had realized before I started searching the internet for days trying to figure this out. Its really this simple...
You just have to click "Allow Network Access to MySQL" from the MAMP MySQL tab.
Really, thats it.
Oh, and you MIGHT have to still change your bind address to either 0.0.0.0 or 127.0.0.1 like outlined in the posts above, but clicking that box alone will probably solve your problems if you are a MAMP user.
Setting the bind-address to the server's network IP instead of the localhost default, and setting privileges on my user worked for me.
my.cnf:
bind-address = 192.168.123.456
MySql Console:
GRANT ALL PRIVILEGES ON dbname.* to username#'%' IDENTIFIED BY 'password';
In my case,
Change the remote machine mysql configuration at /etc/mysql/my.cnf: change
bind-address = 127.0.0.1
to
#bind-address = 127.0.0.1
On the remote machine, change mysql user permissions with
GRANT ALL PRIVILEGES ON *.* TO 'user'#'%' IDENTIFIED BY 'password';
IMPORTANT: restart mysql on the remote machine: sudo /etc/init.d/mysql restart
I've just faced the same problem.
It happened because the MySQL Daemon was binded to the IP of the machine, which is required to make connection with an user that has permission to connect #your_machine.
In this case, the user should have permission to connect USER_NAME#MACHINE_NAME_OR_IP
I wanted remote access to my machine so I changed in my.cnf from
bind-address = MY_IP_ADDRESS
To
bind-address = 0.0.0.0
Which will allow an user from localhost AND even outside (in my case) to connect to the instance.
Both below permissions will work if you bind the MySQL to 0.0.0.0:
USER_NAME#MACHINE_NAME_OR_IP
USER_NAME#localhost
In my case (I am a noob), I was testing Servlet that make database connection with MySQL and one of the Exception is the one mentioned above.
It made my head swing for some seconds but I came to realize that it was because I have not started my MySQL server in localhost.
After starting the server, the problem was fixed.
So, check whether MySQL server is running properly.
In case you are having problem with a set of Docker containers, then make sure that you do not only EXPOSE the port 3306, but as well map the port from outside the container -p 3306:3306. For docker-compose.yml:
version: '2'
services:
mdb:
image: mariadb:10.1
ports:
- "3306:3306"
…
In my case it was an idle timeout, that caused the connection to be dropped on the server. The connection was kept open, but not used for a long period of time. Then a client restart works, while I believe a reconnect will work as well.
A not bad solution is to have a daemon/service to ping the connection from time to time.
As the detailed answer above says, this error can be caused by many things.
I had this problem too. My setup was Mac OSX 10.8, using a Vagrant managed VirtualBox VM of Ubuntu 12.04, with MySQL 5.5.34.
I had correctly setup port forwarding in the Vagrant config file. I could telnet to the MySQL instance both from my Mac and from within the VM. So I knew the MySQL daemon was running and reachable. But when I tried to connect over JDBC, I got the "Communications link failure" error.
In my case, the problem was solved by editing the /etc/mysql/my.cnf file. Specifically, I commented out the "#bind-address=127.0.0.1" line.
The resolution provided by Soheil was successful in my case.
To clarify, the only change I needed to make was with MySQL's server configuration;
bind-address = **INSERT-IP-HERE**
I am using an external MySQL server for my application. It is a basic Debian 7.5 installation with MySQL Server 5.5 - default configuration.
IMPORTANT:
Always backup the original of any configuration files you may modify. Always take care when elevated as super user.
File
/etc/mysql/my.cnf
Line
bind-address = 192.168.0.103 #127.0.0.1
Restart your MySQL Server service:
/usr/sbin/service mysql restart
As you can see, I simply provided the network IP of the server and commented out the default entry. Please note that simply copy and paste my solution will not work for you, unless by some miracle our hosts share the same IP.
Thanks # Soheil
I know this is an old thread but I have tried numerous things and fixed my issue using the following means..
I'm developing a cross platform app on Windows but to be used on Linux and Windows servers.
A MySQL database called "jtm" installed on both systems. For some reason, in my code I had the database name as "JTM". On Windows it worked fine, in fact on several Windows systems it flew along.
On Ubuntu I got the error above time and time again. I tested it out with the correct case in the code "jtm" and it works a treat.
Linux is obviously a lot less forgiving about case sensitivity (rightly so), whereas Windows makes allowances.
I feel a bit daft now but check everything. The error message is not the best but it does seem fixable if you persevere and get things right.
I just restarted MySQL (following a tip from here: https://stackoverflow.com/a/14238800) and it solved the issue.
I had the same issue on MacOS (10.10.2) and MySql (5.6.21) installed via homebrew.
The confusing thing was that one of my apps connected to the database fine and the other was not.
After trying many things on the app that threw the exception com.mysql.jdbc.CommunicationsException as suggested by the accepted answer of this question to no avail, I was surprised that restarting MySQL worked.
The cause of my issue might have been the following as suggested in the answer in the aforementioned link:
Are you using connection pool ? If yes, then try to restart the
server. Probably few of the connections in your connection pool are in closed state.
It happens (in my case) when there is not enough memory for MySQL. A restart fixes it, but if that's the case consider a nachine with more memory, or limit the memory taken by jvms
Go to Windows services in the control panel and start the MySQL service. For me it worked. When I was doing a Java EE project I got this error" Communication link failure". I restarted my system and then it worked.
After that I again got the same error even after restarting my system. Then I tried to open the MySQL command line console and login with root, even then it gave me an error.
Finally when I started the MySQL service from Windows services, it worked.
Had the same.
Removing port helped in my case, so I left it as jdbc:mysql://localhost/
For me the solution was to change in the conf file of mysql server the parameter bind-address="127.0.0.1" or bind-address="x.x.x.x" to bind-address="0.0.0.0".
Thanks.
If you are using hibernate, this error can be caused for keeping open a Session object more time than wait_timeout
I've documented a case in here for those who are interested.
I found the solution
since MySQL need the Localhost in-order to work.
go to /etc/network/interfaces file and make sure you have the localhost configuration set there:
auto lo
iface lo inet loopback
NOW RESTART the Networking subsystem and the MySQL Services:
sudo /etc/init.d/networking restart
sudo /etc/init.d/mysql restart
Try it now
It is majorly because of weak connection between mysql client and remote mysql server.
In my case it is because of flaky VPN connection.
In phpstorm + vagrant autoReconnect driver option helped.
I was experiencing similar problem and the solution for my case was
changing bind-address = 0.0.0.0 from 127.0.0.1
changing url's localhost to localhost:3306
the thing i felt is we should never give up, i tried every options from this post and from other forums as well...happy it works #saurab
I faced this problem also.
As Soheil suggested,
I went to php.ini file at the path C:\windows\php.ini , then I revised port number in this file.
it is on the line mysqli.default_port =..........
So I changed it in my java app as it's in the php.ini file,now it works fine with me.
For Windows :-
Goto start menu write , "MySqlserver Instance Configuration Wizard" and reconfigure your mysql server instance.
Hope it will solve your problem.
After years having the same issue and no permanent solution this is whats solved it for the past 3 weeks (which is a record in terms of error free operation)
set global wait_timeout=3600;
set global interactive_timeout=230400;
Don't forget to make this permanent if it works for you.
If you are using local emulator, you have to use IP address 10.0.2.2 instead of localhost to access to your local MySQL server.
I am trying to write a Java desktop app that can connect to my database made with Microsoft SQL Server Manager to allow me to view and update it. But, I am having trouble getting the connection to work. I've read through a bunch of tutorials and threads here on Stack Exchange of similar problems, and I'm not sure what I'm doing wrong.
The server is called "SQLEXPRESS" using Windows authentication. I downloaded the JDBC driver found here: https://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=11774 installed it in NetBeans by going to "Services-Databases(right click)-New Connection-Add", but I also added it as a library in my project.
When I try this code, I get the exception that the TCP/IP connection failed either because the server isn't running or port 1433 is locked:
try{
String
URL="jdbc:sqlserver://sqlexpress:1433;DatabaseName=GreenhouseManagement";
Connection conn = DriverManager.getConnection(URL,"","");
System.out.println("connected");
}catch(Exception e){
System.out.println("Oops\n"+e);
}
What do I need to change to fix this?
You might need to reconfigure your connection string into this format.
jdbc:microsoft:sqlserver://HOST:1433;DatabaseName=DATABASE
HOST in this case is most likely to be "localhost" since you are connecting on a local machine.
DATABASE will be the name of your database
Reference: http://alvinalexander.com/java/jdbc-connection-string-mysql-postgresql-sqlserver
I wrote a simple code to connect to SQL Server database and to does a simple select statement, this code runs successfully on my local machine over VPN but when I deploy the same code in the servers, then my code is stopping at getting the DB connection object.
It is not even throwing any timeout exception, so I thought of a port issue and checked using telnet which is successful. Can anyone please suggest why this might happen? I am able to get connection object of the same DB from my local machine over VPN.
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
String connectionUrl = props.getProperty("DBURI");
Connection conn=null;
System.out.println(connectionUrl.trim());
conn = DriverManager.getConnection(connectionUrl.trim());
Problem with the sqljdbc jar file , Used any 32 bit one , After replacing the jar , everything worked fine. Thanks
When trying to connect with a remote Oracle database via JDBC I receive the following exception:
java.sql.SQLRecoverableException: IO-fout: The Network Adapter could not establish the connection
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:419)
at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:536)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:228)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:521)
at java.sql.DriverManager.getConnection(DriverManager.java:322)
at java.sql.DriverManager.getConnection(DriverManager.java:358)
The following is my set-up:
Database: Oracle 10g Release 2 Standard Edition
JDBC library: ojdbc6.jar
JDBC driver: oracle.jdbc.driver.OracleDriver
JDBC URL: jdbc:oracle:thin:#9.2.2.2:1521:ORCL where ORCL is database's SID
JDBC User/pwd: Correct username / password
Strange about this problem is that the connection works just fine when I work from work. When I try to connect however from home via an AT&T VPN connection, it doesn't work.
I have confirmed that I can reach the IP address and have also telnetted the ip on port 1521, which works just fine. Connecting to the datasource from a local WebLogic Application Server also works alright. Furthermore, when trying to connect to the database via sqldeveloper I can also reach the database.
I need to reach the database however from a standalone application (for testing purposes). Does anyone have an idea why this problem occurs? And whether there are alternatives for connecting to a remote Oracle Database, alternatives which sqldeveloper and weblogic perhaps use?
Here's an excerpt of the code attempting to connect with the database:
public static void main(String args[]) throws ClassNotFoundException, SQLException {
Class.forName("oracle.jdbc.driver.OracleDriver");
Connection conn = DriverManager.getConnection("jdbc:oracle:thin:#9.2.2.2:1521:ORCL", "user", "pwd");
}
When a client connects to an Oracle server, it first connnects to the Oracle listener service. It often redirects the client to another port. So the client has to open another connection on a different port, which is blocked by the firewall.
So you might in fact have encountered a firewall problem due to Oracle port redirection. It should be possible to diagnose it with a network monitor on the client machine or with the firewall management software on the firewall.
If it is on a Linux box, I would suggest you add the database IP name and IP resolution to the /etc/hosts.
I have the same error and when we do the above, it works fine.
Take a look at this post on Java Ranch:
http://www.coderanch.com/t/300287/JDBC/java/Io-Exception-Network-Adapter-could
"The solution for my "Io exception: The Network Adapter could not establish the connection" exception was to replace the IP of the database server to the DNS name."
I had similar problem before. But this was resolved when I started using hostname instead of IP address in my connection string.
I have a java program that connects to a MS SQL database. The program works perfectly when running through eclipse however I get an error when I run it through AIX:
java.sql.SQLException: Network error IOException: A remote host refused an attempted connect operation.
I can successfully ping the server but am not able to telnet into the server. I am also not able to telnet from my windows desktop.
I am using jtds to connect:
String connectionString = "jdbc:jtds:sqlserver://"+dropez_ip_address+"/"+dropez_db_name;
ResultSet rs = null;
Statement stmt = null;
try{
Class.forName("net.sourceforge.jtds.jdbc.Driver");
Connection conn = DriverManager.getConnection(connectionString, dropez_db_username, dropez_db_password);
stmt = conn.createStatement();
}catch(Exception e){}
Here is some documentation from jTDS regarding the issue, but I am still not able to resolve the issue.
Why do I get java.sql.SQLException: "Network error IOException: Connection refused: connect" when trying to get a connection?
The "Connection refused" exception is thrown by jTDS when it is unable to connect to the server. There may be a number of reasons why this could happen:
- The server name is misspelled or the port number is incorrect.
- SQL Server is not configured to use TCP/IP. Either enable TCP/IP from SQL Server's Network Utility app or have jTDS connect via named pipes (see the URL format for information on how to do this).
- There is a firewall blocking port 1433 on the server.
To check whether TCP/IP is enabled and the port is not blocked you can use "telnet 1433". Until telnet doesn't connect, jTDS won't either. If you can't figure out why, ask your network administrator for help.
If you can't telnet on port 1433, you are blocked by a firewall somewhere in the middle between your machine and the server. That's not a java related problem.
May it be that when you say "it runs perfectly under eclipse but not AIX" you are taking about 2 different computers ? If so, the one with eclipse is not firewalled, the one where you deploy your app is blocked.
But again, nothing to do with java. It's a level 3 error (TCP layer) of TCP-IP model.
Regards,
Stéphane
Your SQL Server database probably doesn't have the TCP/IP protocol enabled, to enable it:
From the Microsoft SQL Server 2005 -> Configuration Tools, open the 'Microsoft SQL Server Configuration Manager'.
Expand ‘SQL Server 2005 Network Configuration’, and then click ‘Protocols for ’.
Right-click ‘TCP/IP’ and then click ‘Enable’. The icon for the protocol will change to show that the protocol is enabled.
For SQL Server 2008: