Strange java lang NoClassDefFoundError in Eclipse

Question

I have a Java project in Eclipse perfectly running smoothly until this afternoon  when I updated some files  including a ant build xml file   When I build the project  the following error appears   java lang NoClassDefFoundError  proj absa FrontEnd ApplicationStarter Caused by  java lang ClassNotFoundException  proj absa FrontEnd ApplicationStarter     at java net URLClassLoader 1 run Unknown Source      at java security AccessController doPrivileged Native Method      at java net URLClassLoader findClass Unknown Source  at     java lang ClassLoader loadClass Unknown Source      at sun misc Launcher AppClassLoader loadClass Unknown Source      at java lang ClassLoader loadClass Unknown Source    Exception in thread  main     Does anyone have a clue where the problem may be

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Another occasion of when java lang NoClassDefFoundError may happen is during the second subsequent attempts to instantiate the class after the first attempt failed for some other exception or error  The class loader seems to cache knowledge that it was not able to instantiate the class on the first attempt but not the reason why  Thus it reports NoClassDefFoundError   So it s a good idea to make sure there were not errors exceptions with an earlier attempt at instantiating the class before going down a rabbit hole trying to troubleshoot the NoClassDefFoundError

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I found that I had a jar in WEB-INF lib that was in my classpath  however when I upgraded it to the latest version  the filename was different   Removing the old jar file from the classpath and adding the new one fixed the problem   Strangely  Eclipse did not seem to warn me that the old jar file was missing and appeared to compile  however nothing was getting compiled  hence the NoClassDefFoundError   The clue for me was that the build classes directory was setup in the project as the output folder but no class files were getting created there after the build

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I thought my problem and its solution could help So i was getting this same error in my eclipse project In my project i have couple of jar files and the NOCLASSDEFERROR was thrown for a file in the jar file   My library files were part of a folder name  lib  in my project heirarchy I changed my folders name to  libs  and voila it worked    I looked into the  classpath file and i had key-value pairs and the entry for my jar file had key named  lib  and hence i thought probably changing from lib could help

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java lang ClassNotFoundException means CLASSPATH issues   Not having a clue implies that you re assuming that the CLASSPATH is set properly  but it s not   If you re building with Eclipse  make sure that the directory where your compiled  class files exists  is in the CLASSPATH  and has the necessary  class files in it   If you re building with Ant  make sure you see something like this in your build xml    lt path id  production class path  gt       lt pathelement location    production classes    gt       lt pathelement location    production resources    gt       lt fileset dir    production lib   gt           lt include name       jar   gt           lt exclude name     junit  jar   gt           lt exclude name      test  jar   gt       lt  fileset gt   lt  path gt    UPDATE  Either you don t have JAVA HOME bin in your PATH or you downloaded the JRE instead of the JDK   Check the directory where you installed Java and see if your  bin directory has javac exe in it   If you don t have a  bin  download the JDK and install it   If you do have a  bin with javac exe in it  check your PATH to see that the Java  bin directory is in the PATH   Once you ve set it  open a command shell and type  javac -version  to ensure that all is well   What JDK did you tell Eclipse to use

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I m seeing this a bit too often lately  Just today I had the issue with a class in the same package as the affected  red-flagged  class    Exiting eclipse and restarting generally works to resolve the red flag on the affected class but sometimes a red flag is left on the project  then I also need to close the project and reopen it as well to get rid of the standalone red flag  It looks quite weird to see a red flag on a project  with no red flags in any of its child directories   With maven project clusters  I close and open all of the projects in the cluster after restarting eclipse

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While this is a wild guess and may not be applicable in your specific situation  this could ve saved me an hour or so   In case you have  converted  a plain project into Java project  by editing  project file and adding appropriate  tag   make sure you also have a proper  specified - my project didn t get built even though Eclipse attempted to and run no builders  success      lt buildSpec gt       lt buildCommand gt           lt name gt org eclipse jdt core javabuilder lt  name gt           lt arguments gt           lt  arguments gt       lt  buildCommand gt   lt  buildSpec gt

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When you launch your program  it stores the launch configuration that you may latter modify  If something changed in your build run process  you may have wrong settings  For example I used to work with maven  and some launch configuration reference a maven2 classpath container  When deleting the launch configuration and running the program again  it can work again

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Ensure that all the libraries you re using in your project are not being referenced from other project int the workspace  That was my problem

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I see that people have already talked about class path  Since there is no accepted answer  I assume it is not related to class path  So I would like to add that  not having package directive can also lead to class not found errors

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This worked for me in eclipse    Goto Project -  Properties Click on Source tab Clear the checkbox -  Allow output folders for source folders Apply the changes and run the project

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Stab in the dark  but I was having the same exact issue  I solved it by deleting the project from my workspace  be careful not to delete from disk   and then re-imported the project and it worked fine  I think mine was caused by a bad windows shutdown  restarting windows correctly did not correct the issue   HTH

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As mentioned above   java lang ClassNotFoundException means CLASSPATH issues    In my setup  I am running Maven to build  instead of Ant  and using Eclipse  instead of Netbeans    Usually  to build and setup the project  I will run  mvn clean    mvn compile    mvn eclipse eclipse  from the Windows command prompt   The last command  mvn eclipse eclipse  updates the project configuration creating  classpath and  project files   To fix the problem  I deleted the two files   classpath and  project  then re-ran the three commands   So depending on your configuration  try to find the classpath project files  make a backup  and delete them   You can also try deleting the target release build folder  whatever is created from the build command  as well   Then try to build package configure your project again

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I had a similar problem and it had to do with the libraries referenced by the java build path  I was referencing libraries that didn t exist anymore when I did an update  When I removed these references  by project started running again   The libraries are listed under the Java Build Path in the project properties window   Hope this helps

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If you are using Eclipse try Project clean and then try to restart the server

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This seems to be a common error  The solution is to    right-click project choose properties choose  Java Compiler  unclick the first box saying  Enable project specific settings  apply save run   Hope this helps in some cases

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go to build path and check for errors in the jar files  they might be moved to somewhere else  if you have errors on the jar files  Remove them and locate them by clicking add external jars   -cnufederer

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both the problem will be because of classpathref  master-classpath   please check the value is correct

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Doing Project- Clean    in Eclipse solved this problem for me

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For me the issue was I had configured another folder under  Run configurations  which had a class without the latest changes  Once I got it removed referred to the correct bin folder  it started working  Hope it helps someone

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BY ABDULHAYEE   NoClassDefFoundError in Java comes when Java Virtual Machine is not able to find a particular class at runtime which was available during compile time  For example if we have a method call from a class or accessing any static member of a Class and that class is not available during run-time then JVM will throw NoClassDefFoundError  It   s important to understand that this is different than ClassNotFoundException which comes while trying to load a class at run-time only and name was provided during runtime not on compile time  Many Java developer mingle this two Error and gets confused   In short NoClassDefFoundError will come if a class was present during compile time but not available in java classpath during runtime  Normally you will see below line in log when you get NoClassDefFoundError  Exception in thread  main  java lang NoClassDefFoundError Exception in thread    main    simply indicate that its    main    thread which is not able to find a particular class it could be any thread so just don   t worry   Difference between this error coming in main thread and other thread is   whenException in thread    main    comes program crashes or shut it self down as opposed to other thread in which case your program will continue to run    Read more  http   javarevisited blogspot com 2011 06 noclassdeffounderror-exception-in html ixzz2jr35SsaZ

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I too was facing the same issue  Then discovered that the path for the lib folder in the classpath was not set properly

[java] Strange "java.lang.NoClassDefFoundError" in Eclipse

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