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

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i'm working on getting database talk java programs.

can give me quick , dirty sample program using jdbc?

i'm getting rather stupendous error:

exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.communicationsexception: communications link failure      last packet sent server 0 milliseconds ago. driver has not received packets server.     @ sun.reflect.nativeconstructoraccessorimpl.newinstance0(native method)     @ sun.reflect.nativeconstructoraccessorimpl.newinstance(nativeconstructoraccessorimpl.java:39)     @ sun.reflect.delegatingconstructoraccessorimpl.newinstance(delegatingconstructoraccessorimpl.java:27)     @ java.lang.reflect.constructor.newinstance(constructor.java:513)     @ com.mysql.jdbc.util.handlenewinstance(util.java:409)     @ com.mysql.jdbc.sqlerror.createcommunicationsexception(sqlerror.java:1122)     @ com.mysql.jdbc.connectionimpl.createnewio(connectionimpl.java:2260)     @ com.mysql.jdbc.connectionimpl.<init>(connectionimpl.java:787)     @ com.mysql.jdbc.jdbc4connection.<init>(jdbc4connection.java:49)     @ sun.reflect.nativeconstructoraccessorimpl.newinstance0(native method)     @ sun.reflect.nativeconstructoraccessorimpl.newinstance(nativeconstructoraccessorimpl.java:39)     @ sun.reflect.delegatingconstructoraccessorimpl.newinstance(delegatingconstructoraccessorimpl.java:27)     @ java.lang.reflect.constructor.newinstance(constructor.java:513)     @ com.mysql.jdbc.util.handlenewinstance(util.java:409)     @ com.mysql.jdbc.connectionimpl.getinstance(connectionimpl.java:357)     @ com.mysql.jdbc.nonregisteringdriver.connect(nonregisteringdriver.java:285)     @ java.sql.drivermanager.getconnection(drivermanager.java:582)     @ java.sql.drivermanager.getconnection(drivermanager.java:207)     @ sqltest.main(sqltest.java:22) caused by: com.mysql.jdbc.exceptions.jdbc4.communicationsexception: communications link failure     last packet sent server 0 milliseconds ago. driver has not received packets server.     @ sun.reflect.nativeconstructoraccessorimpl.newinstance0(native method)     @ sun.reflect.nativeconstructoraccessorimpl.newinstance(nativeconstructoraccessorimpl.java:39)     @ sun.reflect.delegatingconstructoraccessorimpl.newinstance(delegatingconstructoraccessorimpl.java:27)     @ java.lang.reflect.constructor.newinstance(constructor.java:513)     @ com.mysql.jdbc.util.handlenewinstance(util.java:409)     @ com.mysql.jdbc.sqlerror.createcommunicationsexception(sqlerror.java:1122)     @ com.mysql.jdbc.mysqlio.<init>(mysqlio.java:344)     @ com.mysql.jdbc.connectionimpl.createnewio(connectionimpl.java:2181)     ... 12 more caused by: java.net.connectexception: connection refused     @ java.net.plainsocketimpl.socketconnect(native method)     @ java.net.plainsocketimpl.doconnect(plainsocketimpl.java:333)     @ java.net.plainsocketimpl.connecttoaddress(plainsocketimpl.java:195)     @ java.net.plainsocketimpl.connect(plainsocketimpl.java:182)     @ java.net.sockssocketimpl.connect(sockssocketimpl.java:432)     @ java.net.socket.connect(socket.java:529)     @ java.net.socket.connect(socket.java:478)     @ java.net.socket.<init>(socket.java:375)     @ java.net.socket.<init>(socket.java:218)     @ com.mysql.jdbc.standardsocketfactory.connect(standardsocketfactory.java:256)     @ com.mysql.jdbc.mysqlio.<init>(mysqlio.java:293)     ... 13 more

contents of 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" ); // in init         // // edit jdbc url          connection conn = drivermanager.getconnection(              "jdbc:mysql://localhost:3306/projects?user=user1&password=123");         // statement st = conn.createstatement();         // resultset rs = st.executequery( "select * table" );          system.out.println("connected?");     } }

so, have

com.mysql.jdbc.exceptions.jdbc4.communicationsexception: communications link failure
java.net.connectexception: connection refused

i'm quoting this answer contains step-by-step mysql+jdbc tutorial:

if sqlexception: connection refused or connection timed out or mysql specific communicationsexception: communications link failure, means db isn't reachable @ all. can have 1 or more of following causes:

  1. ip address or hostname in jdbc url wrong.
  2. hostname in jdbc url not recognized local dns server.
  3. port number missing or wrong in jdbc url.
  4. db server down.
  5. db server doesn't accept tcp/ip connections.
  6. db server has run out of connections.
  7. something in between java , db blocking connections, e.g. firewall or proxy.

to solve 1 or other, follow following advices:

  1. verify , test them ping.
  2. refresh dns or use ip address in jdbc url instead.
  3. verify based on my.cnf of mysql db.
  4. start db.
  5. verify if mysqld started without --skip-networking option.
  6. restart db , fix code accordingly closes connections in finally.
  7. disable firewall and/or configure firewall/proxy allow/forward port.

see also:


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