com mysql jdbc exceptions jdbc4 CommunicationsException Communications link failure

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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  lt init gt  ConnectionImpl java 787      at com mysql jdbc JDBC4Connection  lt init gt  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  lt init gt  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  lt init gt  Socket java 375      at java net Socket  lt init gt  Socket java 218      at com mysql jdbc StandardSocketFactory connect StandardSocketFactory java 256      at com mysql jdbc MysqlIO  lt init gt  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

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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.

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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

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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

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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

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Also your server might just be closed  On a Mac  navigate to mySQL preference panel through the spotlight  When there  check the box to start your server when your computer starts and start the server

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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

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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

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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

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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

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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

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I was facing the same problem while i was starting my application    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    The issue was that in the mysql file  etc mysql mysql conf d mysqld cnf  the configuration was like that   mysqld  pid-file           var run mysqld mysqld pid socket             var run mysqld mysqld sock datadir            var lib mysql log-error          var log mysql error log   By default we only accept connections from localhost bind-address      127 0 0 1   Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links 0   So as we can see that bind address is pointing to the 127 0 0 1  so for starting your application  a simple solution is that we can use the jdbc mysql   127 0 0 1 3306 pizzeria instead of jdbc mysql   localhost 3306 pizzeria which will connect the mysql to the application or another solution is that you can check and change the mysql configurations to default Both solution can work  I hope it will work for you guys too

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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

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check your wait timeout set on the DB server  Some times it defaults to 10 seconds  This looses the connection in 10 seconds   mysql gt  show global variables like   time       update it make it something like 28800  mysql gt  SET GLOBAL wait timeout   28800

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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

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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

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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  lt  -- https   mvnrepository com artifact mysql mysql-connector-java -- gt   lt dependency gt       lt groupId gt mysql lt  groupId gt       lt artifactId gt mysql-connector-java lt  artifactId gt       lt version gt 8 0 21 lt  version gt   lt  dependency gt     New Jdbc driver  lt  -- https   mvnrepository com artifact org mariadb jdbc mariadb-java-client -- gt   lt dependency gt       lt groupId gt org mariadb jdbc lt  groupId gt       lt artifactId gt mariadb-java-client lt  artifactId gt       lt version gt 2 6 2 lt  version gt   lt  dependency gt

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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

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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  lt uses-permission android name  android permission INTERNET   gt  just after the opening manifest tag  Add the JDBC driver into your Gradle  or Maven  dependencies

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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    lt dependency gt       lt groupId gt mysql lt  groupId gt       lt artifactId gt mysql-connector-java lt  artifactId gt       lt version gt 5 1 38 lt  version gt   lt  dependency gt    All started when I saw the Ankit Jain s answer

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I encountered same problem  I am using spring  amp  dbcp  amp  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

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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

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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

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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    lt dependency gt       lt groupId gt mysql lt  groupId gt       lt artifactId gt mysql-connector-java lt  artifactId gt       lt version gt 5 1 9 lt  version gt   lt  dependency gt    But in the develop environment  I use this    lt dependency gt       lt groupId gt mysql lt  groupId gt       lt artifactId gt mysql-connector-java lt  artifactId gt       lt version gt 5 1 31 lt  version gt   lt  dependency gt    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

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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

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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

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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

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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 amp characterEncoding UTF-8 amp 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

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In my case  I faced this error when trying to connect to mysql-server running inside a container on a Ubuntu host VM from the same host    Example   If my VM name is abc company com   the following jdbc URL would not work   jdbc mysql   abc company com 3306 dbname  Above jdbc url would work fine from other machines like xyz company com but just not abc company com   where as the following jdbc URL would work just fine on abc company com machine   jdbc mysql   localhost 3306 dbname  which led me to check the  etc hosts file    Adding the following line to  etc hosts fixed this issue    127 0 1 1    abc company com    abc  This seems to be an OS bug that requires us to add these on some Ubuntu versions   Reference  https   www debian org doc manuals debian-reference ch05 en html  the hostname resolution  Before trying this  I had tried all other solutions like GRANT ALL    changing the bind-address line in mysql cnf   None of them helped me in this case

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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

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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

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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

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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          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    DB server has run out of connections    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          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 the DB    Verify if mysqld is started without the --skip-networking option    Restart the DB and fix your code accordingly that it closes connections in finally    Disable firewall and or configure firewall proxy to allow forward the port          See also    How should I connect to JDBC database   datasource in a servlet based application  Is it safe to use a static java sql Connection instance in a multithreaded system

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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

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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

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I had the same problem  and here s how it was fixed    My  jsp was calling attributes that I had not yet defined in the servlet  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

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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

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My same problem is solved by the following steps    Go to my cnf  vi  etc mysql my cnf  Modify its bind-address   bind-address   0 0 0 0   Restart MySQL  sudo  etc init d mysql restart

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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

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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

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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   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

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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

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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

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Ensure skip-networking is commented out in my cnf my ini

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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

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For Remote Call to Mysql     Add remote user to Mysql from for exemple  IP remoteIP    mysql -u xxxx -p   local coonection to mysql mysql gt  GRANT ALL PRIVILEGES ON     TO  theNewUser   remoteIP  IDENTIFIED BY  passWord     Query OK  0 rows affected  xx sec  mysql gt  FLUSH PRIVILEGES    Query OK  0 rows affected  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  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

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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

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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  lt username gt   lt password gt      instead of specifying the login parameters     Connection conn   DriverManager getConnection   jdbc mysql   localhost 3306 projects user user1 amp password 123      Regards

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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

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Please update your IP address in  etc mysql my cnf file  bind-address    0 0 0 0   Restart mysql deamon and mysql services

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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

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This question has MANY answers  and I think mine would suit another question better  but the answers to that question are locked  It points to this thread  What solved it for me was appending  amp createDatabaseIfNotExist true to the spring datasource url string in application properties  This was very tricky because it manifested itself in a couple of different  weird  seemingly unrelated errors  and when I tried to fix what it complained about it simply would pop another error up  or the error was impossible to fix  It complained about not being able to load JDBC  saying it wasn t in the classpath  but I added it to the classpath in some 30 different ways and was already facedesking

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If there are any readers who encountered this issue for accessing remote server  make sure the port is open

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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    quot useSSL true quot    quot requireSSL false quot    quot verifyServerCertificate false quot   is translated to sslMode PREFERRED    quot useSSL true quot    quot requireSSL true quot    quot verifyServerCertificate false quot   is translated to sslMode REQUIRED    quot useSSL true quot  AND  quot verifyServerCertificate true quot   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

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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

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

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