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

-

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:


Comments

Post a Comment

Popular posts from this blog

Hatching array of circles in AutoCAD using c# -

-
i beginner in autocad plugins .i have created array of circle using following code. now, have hatch circles in array .how that??how hatch circles @ once? moreover, how can return hatch method , use hatch objects.sorry language.thanks in advance. [assembly: commandclass(typeof(beamsection.class1))] namespace beamsection { public class class1 { //class1 obj = new class1(); [commandmethod("beamatsupport")] public void addlightweightpolyline() { // current document , database document acdoc = application.documentmanager.mdiactivedocument; database accurdb = acdoc.database; promptpointresult ppr = acdoc.editor.getpoint("\nselect starting point "); var ucs = acdoc.editor.currentusercoordinatesystem; point3d startingpt = ppr.value.transformby(ucs); list<double> radius = new list<double>(); radius.add(0.5);
Read more

ios - UITEXTFIELD InputView Uipicker not working in swift -

-
hello trying pop uipickerview view programmatically when user clicks on textfield. have tried doesn't doing anything. isn't working. nothing happening when click textfield class userprofiletableviewcontroller: uitableviewcontroller,uitextfielddelegate,uipickerviewdelegate,uipickerviewdatasource { var itempicker: uipickerview! = uipickerview() @iboutlet weak var gendertxtfield: uitextfield! var gender = ["male","female"] override func viewdidload() { super.viewdidload() gendertxtfield.delegate = self itempicker!.delegate = self itempicker!.datasource = self itempicker!.backgroundcolor = uicolor.blackcolor() self.gendertxtfield.inputview = itempicker } func numberofcomponentsinpickerview(pickerview: uipickerview) -> int{ return 1 } // returns # of rows in each component.. func pickerview(pickerview: uipickerview, numberofrowsincomponent component:
Read more

Python Pig Latin Translator -

-
so have been working on @ codecademy.com while trying learn python. don't know if blind , can't see why won't work or what. here's code won't let me use. function print variable if had typed in , print "empty" if didn't type anything. print "welcome english pig latin translator!" original = raw_input("what's name?") if len(original) > 0 print original else print "empty" if len(original) > 0 else the above lines contains syntax errors. try: if len(original) > 0: else: note added colons, ( : ).
Read more