This question already has answers here:
Connect to remote MySQL database through SSH using Java
(6 answers)
Closed 2 years ago.
I'm studying to be a new developer. I've rent an AWS virtual machine with Bitnami and LAMP to practice in my exercises about Java and MySQL databases.
I have a problem with the connection. I can connect to the server with SSH in the terminal but, I can`t connect with my Java programs... I try to use Jsch and I've found an example to use my Key Pair but, I don't know how I connect to the database directly with Java using the Key Pair.
Can anybody tell me a link to learn about Jsch? Does some code solution this?
Thanks for readme! That is my first question!!
Thanks for the answers!! I have resolved the problem with the help of two links.
In this link, you can see how to create an SSH -L in Java. It explains all the parameters. https://ayoub.io/2016/06/29/using-jsch-for-ssh-port-forwarding-java.html
But this is not a complete solution because my code had an Exception. In this other link, you have the solution. com.jcraft.jsch.JSchException: UnknownHostKey
I hope that this helps someone.
This question already has answers here:
JDBC connection failed, error: TCP/IP connection to host failed
(9 answers)
Closed 5 years ago.
I have a local MS SQL Server Express 2016 running on 1433. I can connect to it via MS SQL Management Studio and HeidiSQL just fine.
In Eclipse Neon I created a new JPA project. I want to create entities from my DB. So I click on JPA Tools -> Generate Entities from Tables.... In the following dialog window I click on the Add connections... icon. By searching the internet I found two different approaches for continuing from here:
a) Connection Profile Type: SQL Server
b) Connection Profile Type: Generic JDBC
a) In the following window I add a new driver, specify the path to my sqljdbc42.jar and set all the properties (Driver Class: com.microsoft.sqlserver.jdbc.SQLServerDriver). The weird thing, when I chose this driver, in the Properties section nothing shows up and I get the following error:
b) Similar to a) I add a new driver, specify the path to the jar file and set all the properties. This time I get one step further: I can press the Test Connection button. If I do so however, the window freezes for a few seconds and then shows a Ping failed! error.
I guess the URL is wrong so I tried a lot of different variations but none of them worked. Here are a few of them (but I tried many more):
jdbc:sqlserver://MyPcName\SQLEXPRESS:1433
jdbc:sqlserver://MyPcName\SQLEXPRESS
jdbc:sqlserver://MyPcName\SQLEXPRESS:1433
jdbc:sqlserver://MyPcName\SQLEXPRESS
jdbc:sqlserver://localhost:1433
jdbc:sqlserver://MyPcName\SQLEXPRESS:1433;DatabaseName=MyDb
As mentioned above, connecting via Management Studio or HeidiSQL works (with the username test and no password). And while it should not matter since the server is running locally I tried turning of the firewall and it did not help either.
I still don't know why a) does not work but I figured out my issue with b). MS SQL Management Studio and HeidiSQL did connect to the database via named-pipe instead of tcp and the tcp connection was not actually setup. Following the steps in this answer solved it:
https://stackoverflow.com/a/24299346/4961688
This question already has answers here:
RMI cannot connect to remote server
(2 answers)
Closed 9 years ago.
I can't seem to connect 2 machines using RMI. To make sure there wasn't something wrong with my code I copied the simple example from wikipedia (http://en.wikipedia.org/wiki/Java_remote_method_invocation) and I edited the code to print out a simple int.
I tried giving all permissions and turning all the firewalls off and I still get this error:
java.rmi.ConnectException: Connection refused to host 55.229.xx.xxx; nested
exception is:java.net.ConnectException: Connection timed out: connect
I've been trying to do this for the past 3 days and I still can't seem to get past basic configuration problems.
The Problem could be your RMI server is sending back its local address, instead of WAN address.
System.setProperty("java.rmi.server.hostname", *host IP*);
also take a look at security policies regarding RMI:
http://docs.oracle.com/javase/tutorial/rmi/running.html
Check your firewall settings on your aws instance
RMI is running on 1099 port by default as i remember.
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.
I am getting the error: "The Network Adapter could not establish the connection" from a web application deployed in Oracle Application Server 10g. The database is local, so there shouldn't be any connection issues.
First test: I can connect to the DB no problem from SQL plus, run queries, etc.
Second test: I can connect to the database no problem from a locally installed JDeveloper on the server, and run queries, etc. no problem. This works with the short JDBC scring, and the long one (shown below).
jdbc:oracle:thin:#(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521)))(CONNECT_DATA=(SERVICE_NAME=abcd)(SERVER=DEDICATED)))
Yet when I run the web app, it gives the above error. It seems too generic for me to do anything about.
Any suggestions on how to solve this? I assume that Oracle logs failed connection attempts somewhere, but I couldn't find anything relevant in the databases alert.log file.
It is possible that the problem is that the application is using an old jsdk, but I would assume that then some version mismatch error would be given instead of a "network connection" message.
Edit: I don't know whether this is an OAS problem or a problem with the specific Web Application, I would like to figure this out first, as it seems it should be easy. In WebSphere, there is a "test connection" button to dest data-sources you have added, but it seems there is no such functionality in OAS10? Somehow I think there must be, and I am just missing it because I am not an OAS expert.
Edit 2: I installed JDevelop on a remote machine and connected to the database with no problems, so I know for sure it isn't an issue with the database connectivity itself - it seems like it must be a problem within OAS?
I faced similar problem(able to connect through client but not web application) with Oracle XE when running with default configuration. Increasing number of sessions and processes solved my problem. Check this http://www.markcallen.com/oracle/oracle-xe-tuning.
I assume that Oracle logs failed connection attempts somewhere
It would show up in listener.log, but with the error you get, it seems doubtful that JDBC could even contact the listener.
jdbc:oracle:thin:#(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521)))(CONNECT_DATA=(SERVICE_NAME=abcd)(SERVER=DEDICATED)))
Is that the same string you use for the web app?
I've had issues with localhost and 127.0.0.1 which go away when using a more definitive host name or address [IE a name that other machines would know the host as.]. I think it was to do with how the name was resolved (eg locally or off to a name server or similar).
Not a java person, but is there any way to simply ping localhost/127.0.0.1 from the java and see whether there's a response.
One of the ways to fix the issueis to update Hosts file at WAS Server with entries for DB servers as shown below:
111.222.333.444 serverab.abc.com serverab