java lang UnsupportedClassVersionError Bad version number in class file

Question

I am getting this error when I include an opensource library that I had to compile from source   Now  all the suggestions on the web indicate that the code was compiled in one version and executed in another version  new on old    However  I only have one version of JRE on my system   If I run the commands     javac -version javac 1 5 0 18    java -version java version  1 5 0 18  Java TM  2 Runtime Environment  Standard Edition  build 1 5 0 18-b02  Java HotSpot TM  Server VM  build 1 5 0 18-b02  mixed mode    and check in Eclipse for the properties of the java library  I get 1 5 0 18  Therefore  I have to conclude something else  internal to a class itself  is throwing the exception   Is that even possible

User · Answer

i solved  this problem by changing jre required for server  in my case is tomcat   From Server tab in eclipse  double click on the server  in order to open page for server configuration   click on Runtime environment  then change JRE required

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Always check for the obvious too   I got this error once when I accidently grabbed the wrong resource for the server s add and remove action   It can be easy to overlook

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I also got the same error  Reason for that I was compiling the project using Maven  I had JAVA HOME pointing to JDK7 and hence java 1 7 was being used for compilation and when running the project I was using JDK1 5  Changing the below entry in  classpath file or change in the eclipse as in the screenshot resolved the issue   classpathentry kind  con  path  org eclipse jdt launching JRE CONTAINER org eclipse jdt internal debug ui launcher StandardVMType J2SE-1 5   or change in the run configuarions of eclipse as

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I ve learned that error messages like this are usually right  When it couldn t POSSIBLY  in your mind  be what the error being reported says  you go hunting for a problem in another area   only to find out hours later that the original error message was indeed right   Since you re using Eclipse  I think Thilo has it right The most likely reason you are getting this message is because one of your projects is compiling 1 6 classes  It doesn t matter if you only have a 1 5 JRE on the system  because Eclipse has its own compiler  not javac   and only needs a 1 5 JRE to compile 1 6 classes   It may be weird  and a setting needs to be unchecked to allow this  but I just managed to do it   For the project in question  check the Project Properties  usually Alt Enter   Java Compiler section  Here s an image of a project configured to compile 1 6  but with only a 1 5 JRE

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changing the project to use java 1 7  For this to work follow those steps     Change Compiler Compliance Level Change your projects JRE JDK to something of the same level 1 7 in my case  Do the same change in all the projects referenced by your project Change your run debug configuration to use the JRE JDK  or of the same level    Not working     delete projects Bin directory Clean reBuild   Still not working   in your project s directory  edit  settings org eclipse jdt core prefs   make sure your target level is applied  Good Luck

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Did you compile with Eclipse  It uses a different compiler  not javac   That should not result in this error  if everything is configured properly   but you can try to compile it with javac instead   If that fixed the problem  try to see if Eclipse has some incorrect compiler settings  Specifically have it target Java 5

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Another scenario where this could happen is when you are launching an instance of eclipse  for debug etc   from a host eclipse - in which case  altering the project s level or JRE library on the project s classpath alone doesn t help  What matters is the JRE used to launch the target eclipse environment

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Also check any jar files in your project that have been compiled for a higher version of Java  If these are your own libraries  you can fix this by changing the target version attribute to javac   lt javac destdir    classes dir               debug  on  classpathref  project classpath  target  1 6  gt

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Deleting the project specific settings files  Eclipse workspace project folder  settings   from the project folder also will do   Obviously  we need to do a project clean and build after deleting

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Have you tried doing a full  clean  and then rebuild in Eclipse  Project- Clean         Are you able to compile and run with  javac  and  java  straight from the command line   Does that work properly   If you right click on your project  go to  Properties  and then go to  Java Build Path   are there any suspicious entries under any of the tabs   This is essentially your CLASSPATH   In the Eclipse preferences  you may also want to double check the  Installed JREs  section in the  Java  section and make sure it matches what you think it should   You definitely have either a stale  class file laying around somewhere or you re getting a compile-time run-time mismatch in the versions of Java you re using

[java] java.lang.UnsupportedClassVersionError: Bad version number in .class file?

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