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

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:

  1. IP address or hostname in JDBC URL is wrong.
  2. Hostname in JDBC URL is not recognized by local DNS server.
  3. Port number is missing or wrong in JDBC URL.
  4. DB server is down.
  5. DB server doesn’t accept TCP/IP connections.
  6. DB server has run out of connections.
  7. 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:

  1. Verify and test them with ping.
  2. Refresh DNS or use IP address in JDBC URL instead.
  3. Verify it based on my.cnf of MySQL DB.
  4. Start the DB.
  5. Verify if mysqld is started without the --skip-networking option.
  6. Restart the DB and fix your code accordingly that it closes connections in finally.
  7. Disable firewall and/or configure firewall/proxy to allow/forward the port.

See also:

Related Posts:

  1. com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
  2. java.sql.SQLException: No database selected – why?
  3. Cannot issue data manipulation statements with executeQuery()
  4. java.lang.ClassNotFoundException: com.mysql.jdbc.Driver in Eclipse
  5. java.lang.ClassNotFoundException: com.mysql.jdbc.Driver in Eclipse
  6. getting error HTTP Status 405 – HTTP method GET is not supported by this URL but not used `get` ever?
  7. Can’t find mysqladmin on Mac OSX 10.6.8
  8. DB2 jdbc connection error Connection refused. ERRORCODE=-4499, SQLSTATE=08001
  9. A JNI error has occurred, please check your installation and try again in Eclipse x86 Windows 8.1
  10. Unable to create requested service [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]
  11. DB2 SQL Error: SQLCODE=-204, SQLSTATE=42704
  12. java.sql.SQLException: Access denied for user ‘root’@’localhost’ (using password: YES)
  13. ResultSet exception – before start of result set
  14. java.lang.ClassNotFoundException: sun.jdbc.odbc.JdbcOdbcDriver Exception occurring. Why?
  15. IO Error: The Network Adapter could not establish the connection
  16. Getting java.sql.SQLException: Operation not allowed after ResultSet closed
  17. How do I get the size of a java.sql.ResultSet?
  18. SQL Error: 0, SQLState: 08S01 Communications link failure
  19. How to resolve Unable to load authentication plugin ‘caching_sha2_password’ issue
  20. Efficient way to do batch INSERTS with JDBC
  21. What kind of Java type is “[B”?
  22. Connection Java – MySQL : Public Key Retrieval is not allowed
  23. JPA or JDBC, how are they different?
  24. Could not reserve enough space for object heap
  25. What does “Could not find or load main class” mean?
  26. Exception in thread “main” java.util.NoSuchElementException
  27. “Error occurred during initialization of VM; Could not reserve enough space for object heap” using -Xmx3G
  28. What’s the simplest way to print a Java array?
  29. javax vs java package
  30. A JNI error has occurred, please check your installation and try again in Eclipse x86 Windows 8.1
  31. What is a stack trace, and how can I use it to debug my application errors?
  32. How to fix “A JNI error has occurred, please check your installation.”
  33. Java Runtime Environment not found error when I open an application
  34. “PKIX path building failed” and “unable to find valid certification path to requested target”
  35. What exactly does a jar file contain?
  36. JavaFX – Exception in Application start method? [duplicate]
  37. How is “mvn clean install” different from “mvn install”?
  38. JRE Missing when installing eclipse
  39. What does “?” mean in Java? [duplicate]
  40. When is the @JsonProperty property used and what is it used for?
  41. Print ArrayList
  42. “Missing return statement” within if / for / while
  43. Understanding regex in Java: split(“\t”) vs split(“\\t”) – when do they both work, and when should they be used
  44. Make copy of an array
  45. How can I convert a .jar to an .exe?
  46. Error: NoClassDefFoundError: org/apache/commons/logging/LogFactory
  47. Illegal Escape Character “\”
  48. Error – trustAnchors parameter must be non-empty
  49. Calculating the angle between the line defined by two points
  50. Wait for page load in Selenium
  51. What does regular expression \\s*,\\s* do?
  52. Constructor cannot be applied to given types?
  53. Printing HashMap In Java
  54. Java “.class expected”
  55. Java Initialize an int array in a constructor
  56. Java – Best way to print 2D array?
  57. “cannot find symbol: method” but the method is declared
  58. No enclosing instance of type is accessible.
  59. How to remove single character from a String
  60. What is the best math library to use with java?
  61. What is the difference between a null array and an empty array?
  62. Why is there no String.Empty in Java?
  63. How to initialize List object in Java?
  64. PrintWriter append method not appending
  65. How do I use the JAVA_OPTS environment variable?
  66. What is the difference between iterator and iterable and how to use them?
  67. Netbeans installation doesn’t find JDK
  68. Convert String to int array in java
  69. eclipse won’t start – no java virtual machine was found
  70. What causes “‘void’ type not allowed here” error
  71. Variable might not have been initialized error
  72. Java substring: ‘string index out of range’
  73. throw checked Exceptions from mocks with Mockito
  74. Java GUI: about getContentPane( ) method and content
  75. Hibernate Error: a different object with the same identifier value was already associated with the session
  76. How to solve the “failed to lazily initialize a collection of role” Hibernate exception
  77. Initializing multiple variables to the same value in Java
  78. Java: Unresolved compilation problem
  79. FXML Load exception
  80. NullPointerExcetion Native Method Accessor… Hashing Words Issue
  81. Get keys from HashMap in Java
  82. Determine if a String is an Integer in Java [duplicate]
  83. How do I run Java .class files?
  84. Fill an array with random numbers [duplicate]
  85. Whitespace Matching Regex – Java
  86. Size has private access in ArrayList
  87. Keylistener not working for JPanel
  88. the getSource() and getActionCommand()
  89. Failed to install android-sdk: “java.lang.NoClassDefFoundError: javax/xml/bind/annotation/XmlSchema”
  90. Maven build Compilation error : Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project Maven
  91. Regex pattern including all special characters
  92. Error: ‘)’ expected compiler error
  93. How does addNotify() and requestFocus() work in Java with JPanel?
  94. DTO and DAO concepts and MVC
  95. How to extract .war files in java? ZIP vs JAR
  96. How to print a table of information in Java
  97. set background color: Android
  98. Class Declarations for temperature program in Java
  99. Spring Boot – Cannot determine embedded database driver class for database type NONE
  100. Convert double to float in Java

Leave a Comment

techhipbettruvabetnorabahisbahis forumutaraftarium24edueduedusedusedusedueduseduseduedus