This question already has answers here:
Connect Java to a MySQL database
(14 answers)
Closed 6 months ago.
I am creating a java game and I need to upload it to web, I discovered the webswing that converts the jar to a web version, I tested it to jar without database connection and it worked, but when I try to connect to a mysql database it return a error:
Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException: java.sql.SQLException: No suitable driver found for jdbc:mysql://localhost:3306/dreamland
Error into webswing executable
I am using xampp to localhost database and I don't know if it's because that it can not connect
Picture of all applications on webswing
The "jogoDreamland" application is the one that's getting the error
Configuration of "jogoDreamland"
I only modified these two, the class path I added the path to where my main class is on the project and on main class I added the package.formsLogin
The buttons that causes the errors
When I click one of these two buttons it returns the error from above, when I launch it on desktop, it runs normally and connect to the database, the problem is when I use it on webswing
mysql connector version
The connection to the database
Code that the method on the button runs, that use the db
Another code that the method on the button runs, that use the db
Currently, only these two methods are loaded when I click the button.
At any point in time you should be aware where your application is running.
So if you run a Java Swing application on your desktop, it is running on your desktop computer. If you push this same application into WebSwing, it becomes a webapp that you have to install on some server. Via your browser you connect to that server to see the UI but it's still running on the server.
To get the database connection, the application has to connect to wherever your database is running. If you left that on the local computer, your server has to connect to the local computer. Probably it is better to install the database either on the same server or on a server close to the machine running the Webswing application.
You error message though indicates you wrapped your application but forgot to add the mysql jdbc driver.
I use H2 database (file) in my Java app and due to some data appearance problem in IntelliJ, I use file option instead of memory.
Here is my url setting in application.properties:
spring.datasource.url=jdbc:h2:file:~/test-db;
DB_CLOSE_DELAY=-1;DATABASE_TO_UPPER=false;AUTO_SERVER=TRUE
I can connect and see table data via IntelliJ and H2 console by using the url parameter as shown below:
jdbc:h2:file:~/test-db
However, even I connect to the database successfully, the table data is not seen in DBeaver as shown below:
I think I should use tcp option to connect H2 daabase, but I cannot by using the following settings:
spring.datasource.url=jdbc:h2:tcp://localhost/~/test-db
or
jdbc:h2:tcp://localhost/C:/test-db
and get "Unable to open JDBC Connection for DDL execution" error (I use Windows). Any idea?
You're using a file-associated connection to that in-memory DB that can only be used by 1 tool at once.
So when IntelliJ is connected it generates a lock-file to protect it against multi-access.
I would suggest a TCP connection that allows multiple connections - see redundant question here:
H2 database error: Database may be already in use: "Locked by another process"
This question already has answers here:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
(51 answers)
Closed 4 years ago.
I am getting an error (exceptions) while deploying my project. Some time ago the project was working but now it is not working. Please tell me a solution to get rid of this.
You dont provide any code so i ll answer about the error. Link Failure usually means that there was a problem trying to communicate with a service. This means, it seems like your jsp couldn't connect to your database on a connection level. Do you have your DB instance listening on localhost? Do you have firewalls in place that's preventing communication between your jsp and your DB instance? Have you checked the internet connection? The link? Maybe its usefull to check this Solving a "communications link failure" with JDBC and MySQL
It seems you forgot to include MySql connector into library. Please check if MySql connector is available in your project library.
As no code is provided, I just go trough troubleshooting from your GlassFish application server. I suppose you are using connection pool to connect to DB. Are you able to ping your connection pool? You might try via admin console or command line :
asadmin> ping-connection-pool myPool
I have a small HSQLDB program to test bits of SQL. I am getting this error:
A pre-version 2.0 client attempted to connect. We rejected them.
Yet the only JDBC driver I have is the HSQLDB v2.3 in the most recent download:
hsqldb/lib/hsqldb.jar
I'm using this string to load the JDBC driver:
Class.forName("org.hsqldb.jdbcDriver");
And the connection string is:
connectionStr = "jdbc:hsqldb:hsql://localhost/tmp_db";
user=sa, password=
Default values. My HSQLDB server seems to have started OK with a database as follows:
server.dbname.0=**tmp_db**
server.database.0=file:r:/.data/hsqldb/**tmp_db/tmp**
[Server#372f7a8d]: Database [index=2, id=2, db=file:r:/.data/hsqldb/**tmp_db/tmp**, alias=tmp_db] opened sucessfully in 26 ms.
I'm using Netbeans and when I connect via the Services tab, the database seems to be opening OK. Wouldn't Netbeans be using the same driver? Can I check that?
The big question is how do we specify the version 2 client connection, driver or parameters? Must I get a different JAR for the correct driver?
One last thing. The test program works fine if I use a file based connection, such as:
jdbc:hsqldb:db_file
Frustratingly too, the server connection string seemed to be working earlier today. At least I could drop/create tables while I was making changes.
You must use the same jars (or at least recent, compatible versions) on the client and server.
The error shows you are using the 2.x version jar on the server but a 1.8 jar on the client. Check NetBeans to see if some extension you have loaded has the old driver. You can use the correct jar in your NetBeans project by adding it as a library.
If the error is not from NetBeans, check your application's classpath and make sure you have the latest jar in it.
This question already has answers here:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
(51 answers)
Closed 6 years ago.
My program that connects to a MySQL database was working fine. Then, without changing any code used to set up the connection, I get this exception:
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.
What happened?
The code used to get the connection:
private static Connection getDBConnection() throws SQLException, InstantiationException, IllegalAccessException, ClassNotFoundException {
String username = "user";
String password = "pass";
String url = "jdbc:mysql://www.domain.com:3306/dbName?connectTimeout=3000";
Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection(url, username, password);
return conn;
}
This is a wrapped exception and not really interesting. It is the root cause of the exception which actually tells us something about the root cause. Please look a bit further in the stacktrace. The chance is big that you'll then face a SQLException: Connection refused or SQLException: Connection timed out.
If this is true in your case as well, then all the possible causes are:
IP address or hostname in JDBC URL is wrong.
Hostname in JDBC URL is not recognized by local DNS server.
Port number is missing or wrong in JDBC URL.
DB server is down.
DB server doesn't accept TCP/IP connections.
Something in between Java and DB is blocking connections, e.g. a firewall or proxy.
To solve the one or the either, follow the following advices:
Verify and test them with ping.
Refresh DNS or use IP address in JDBC URL instead.
Verify it based on my.cnf of MySQL DB.
Start it.
Verify if mysqld is started without the --skip-networking option.
Disable firewall and/or configure firewall/proxy to allow/forward the port.
By the way (and unrelated to the actual problem), you don't necessarily need to load the JDBC driver on every getConnection() call. Just only once during startup is enough.
check your wait timeout set on the DB server.
Some times it defaults to 10 seconds. This looses the connection in 10 seconds.
mysql> show global variables like '%time%' ;
update it make it something like 28800
mysql> SET GLOBAL wait_timeout = 28800;
I've been having this issue also for about 8-9 days.
Here's some background: I'm developing a simple Java application that runs in bash.
Details:
Spring 2.5.6
Hibernate3.2.3.ga
With maven.
(The base of the project is from mkyong.com , the spring tutorial without anotations )
MySQL version:
[jvazquez#archbox ~]$ mysql --version
mysql Ver 14.14 Distrib 5.5.9, for Linux (i686) using readline 5.1
Linux archbox 2.6.37-ARCH #1 SMP PREEMPT Fri Feb 18 16:58:42 UTC 2011 i686 Intel(R) Core(TM)2 Quad CPU Q8200 # 2.33GHz GenuineIntel GNU/Linux
The application works fine in Arch Linux, Mac OS X 10.6, and FreeBSD 7.2.
When I moved the jar file to another arch linux in a different host, using the same mysql, a similar my.cnf, and the similar kernel version, the connection died and obtained the same error as the original poster:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException:
Communications link failure
I tried every possible combination for this that I found on so and the forums (http://forums.mysql.com/read.php?39,180347,180347#msg-180347 for example, which is closed now and I can't post .. ), specifically:
Triple check that I wasn't using skip
networking. (verified with ps aux
and the my.cnf)
Tried enable log_warnings=1 in the my.cnf but obviously, I wasn't hitting the
server so I didn't saw anything while using the app
SHOW ENGINE innodb STATUS didn't show anything at all; during the tests I could connect via shell, and php also connected to the mysql server
/etc/hosts has localhost 127.0.0.1
Tried the jdbc properties using localhost and 127.0.0.1 with no results
Tried adding c3p0 and changed the max_wait
Max connections in the my.cnf was changed to 900 , 2000 and still nothing my.cnf
Added wait_timeout = 60 my.cnf
Added net_wait_timeout = 360 my.cnf
Added the destroy-method="close" spring.xml
As it was pointed out (if you look up for the same exception , you will find several so threads about the issue Reproduce com.mysql.jdbc.exceptions.jdbc4.CommunicationsException with a setup of Spring, hibernate and C3P0
for example ).
If you are using tomcat, please check the security exception (again, it is on SO, you will find it )
Check that you can resolve that url that you are using
Try adding c3p0.
Verify that there isn't a firewall rejecting your connections
Finally , if you are using GNU/Linux ( ARch linux for example and you indeed obtain this exception )
Try
MySQL Forums :: JDBC and Java :: EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost
If the link get's removed, just add mysqld:ALL to /etc/hosts.allow
I know that is a bit extense, but it may help anybody using GNU/Linux and having this exception and this thread seemed the best place to post my research.
Hope it helps
I got the same error
but then I figured it out its because the Mysql server is not running at that time.
So to change the status of the server
Go to Task Manager
Go to Services
then search for your Mysql server(eg:for my case its MYSQL56)
then you will see under the status column it says its not running
by right clicking and select start
Hope this will help.
We have a piece of software (webapp with Tomcat) using Apache commons connection pooling, and worked great for years. In the last month I had to update the libraries due to an old bug we were encountering. The bug had been fixed in a recent version.
Shortly after deploying this, we started getting exactly these messages. Out of the thousands of connections we'd get a day, a handful (under 10, usually) would get this error message. There was no real pattern, except they would sometimes cluster in little groups of 2 to 5.
I changed the options to on the pool to validate the connection every time one is taken from or put back in the pool (if one is found bad, a new one is generated instead) and the problem went away.
Have you updated your MySQL jar lately? It seems like there may be a new setting that didn't used to be there in our (admittedly very old) jar.
I agree with BalusC to try some other options on your config, such as those you're passing to MySQL (in addition to the connection timeout).
If this failure is transient like mine was, instead of permanent, then you could use a simple try/catch and a loop to keep trying until things succeed or use a connection pool to handle that detail for you.
Other random idea: I don't know what happens why you try to use a closed connection (which exception you get). Could you be accidentally closing the connection somewhere?
Ensure skip-networking is commented out in my.cnf/my.ini
As BalusC mentioned, it would be very useful to post the full stacktrace (always post a full stacktrace, it is useless and frustrating to have only the first lines of a stacktrace).
Anyway, you mentioned that your code was working fine and that this problem started suddenly to occur without any code change so I'm wondering if this could be related to you other question Problem with not closing db connection while debugging? Actually, if this problem started while debugging, then I think it is (you ran out of connections). In that case, restart you database server (and follow the suggestions of the other question to avoid this situation).
I encountered same problem. I am using spring & dbcp & mysql 5.5But If I change localhost to 192.168.1.110 then everything works. What make things more weird is mysql -h localhost just works fine.
update: Finally found a solution. Changing bindaddress to localhost or 127.0.0.1 in my.conf will fix the problem.
In my case, the local loopback interface wasn't started, so "localhost" couldn't be resolved.
You can check this by running "ifconfig" and you should see an interface called "lo". If it is not up, you can activate it by running "ifup lo" or "ifconfig lo up".
In my case, the mysql.com downloaded Connector/J 5.1.29 .jar had this error whereas the 5.1.29 .jar downloaded from the MvnRepository did not.
This happened when building a Google appengine application in Android Studio (gradle, Windows x64), communicating to a Linux MySQL server on the local network/local VM.
I see you are connecting to a remote host. Now the question is what type of a network are you using to connect to the internet?
WINDOWS
If it's a mobile broadband device then get your machines IP address and add it to your hosting server so that your host server can allow connections coming from your machine.[your host might have turned this off due to security reasons].
Note that every time you use a different network device your IP changes.
If you are using a LAN then set a static IP address on your machine then add it to your host.
I hope this helps!! :)
I got the communications failure error when using a java.sql.PreparedStatement with a specific statement.
This was running against MySQL 5.6, Tomcat 7.0.29 and JDK 1.7.0_67 on a Windows 7 x64 machine.
The cause turned out to be setting an integer to a string parameter and a string to an integer parameter then trying to perform executeQuery on the prepared statement. After I corrected the order of parameter setting the statement performed correctly.
This had nothing to do with network issues as the wording of the error message suggested.
The escential problem is that Mysql JDBC pool connections is not used, then the Timeout from Mysql, close the Connections. You need change the pool Parameters to get restart connection when the connection has failures, on this way:
Connection Validation: Required (Check)
Validation Method: autocommit
You can change the Validation Method if you cannot get it works!
If you use WAMP, make sure it is online. What I did was, first turned my firewall off, then it worked, so after that I allowed connection for all local ports, specially port 80. Than I got rid of this problem. For me it was the Firewall who was blocking the connection.
I had the same problem and I used most of the params (autoreconnect etc..), but didn't try the (test_on_idle, or test_on_connect) , I am going to do them next.
However, I had this hack that got me through this:
I have a cron job called Healthcheck, It wakes up every 10 mins and makes a REST API call to the server. The web / app server picks this up, connects to the db, makes a small change and comes back with a 'yes all quiet on western front' or 'shitshappening'. When the latter, it sends a pager / email to the right people.
It has the side effect of always keeping the db connection pool fresh. So long as this cron is running, I don't have the db connection timeout issues. otherwise, they crop up.