Why is Ant giving me a Unsupported major minor version error

Question

I m running this target in Ant   lt target name  quot compile quot  depends  quot init quot      description  quot compile the source  quot   gt       lt  -- Compile the java code from   src  into   build  -- gt       lt javac srcdir  quot   src  quot  destdir  quot   build  quot   gt   lt  target gt   It s giving me this error   C  Users    workspace    build xml 21  java lang UnsupportedClassVersionError       com sun tools javac Main   Unsupported major minor version 51 0  Here are the versions  Apache Ant TM  version 1 8 2  JDK version is JDK 1 7 0  Here s my Compiler settings in Eclipse   Please help me resolve it

User · Answer

Check if tools jar used during compilation complies with the JRE set  If you are on eclipse  verify the versions as  Goto Window- Preferences  - Check Ant Runtime by selecting Runtime under Ant in the left pane  Check the Global Entries under classpath tab  You can see the version in folder path   - On the left pane check installed JREs under Java  Check the version  I had also got the same problem when my selected JRE was 1 6 0 24 and tools jar in Ant runtime was coming from jdk 1 7 If both of them are from different versions- 1 6 1 7  correct them by correcting their path  Typically  tools jar can be found at  C  Program Files Java jdk1 x x lib  Likewise if required add the JRE by pointing it to C  Program Files Java jdk1 x x

User · Answer

If you re getting this error because you re purposefully trying to build to Java 6  but you have Java 7 elsewhere in Eclipse  then it may be because you are referencing a Java 7 tools jar in a Java 6 environment   You ll need to install the JDK 6  not JRE  and add the JRE 6 tools jar as a User Entry in the Classpath of the build configuration  listed above the JRE 7 tools jar

User · Answer

go to run option--- select external tool option ---- external tool configuration---  select ant build ----  select your build xml --- there you will find JDK option--- select your required JRE

User · Answer

Simply just check your run time by go to ant build configuration and change the jre against to jdk  if jdk 1 7 then jre should be 1 7      enter image description here

User · Answer

I d like to add my results here to help others  as while relevant  none of these solved my problem  I had the unique situation where I went from workshop for weblogic 9 2 to Helios with JDK6   However our security experts pushed us on to JDK7  which forced my hand to go to Indigo    In the end I used sysinternals process explorer to find if anything was currently using the JDK6 folder that still existed on my system   Sure enough it was Eclipse    I opened up eclipse ini and the second line was referencing the JDK6  I replaced this with the JDK7 directory  started Eclipse  and the build was successful

User · Answer

One possible cause of this is an incorrect JRE selected in the Ant build options   After right-clicking the build xml and choosing  Run As     and then  Ant Build      make sure the correct JRE is chosen under the JRE Tab of the configuration options dialogue box   You will see a  Separate JRE  option  make sure the appropriate jdk is chosen from the drop down before clicking  Run

User · Answer

You would need to say which version of Ant and which JVM version    You can run ant -v to see which settings Ant is using as per the doc   Ant 1 8  requires JDK 1 4 or higher   The  Unsupported major minor version 51 0  means somewhere code was compiled for a version  of the JDK  and that you are trying to run those classes under an older version of the JDK   see here

User · Answer

Download the JDK version of the JRE to the installed JRE s and use that instead  In Eclipse Indigo  if you check the classpath tab on the run configuration for ant  you will see that it defaults to adding the tools jar from the system  So if you launch Eclipse using Java7 and run an ant build using a separate JRE6 it generates an UnsupportedClassVersionError  When I added the JDK version Eclipse picked up the tools jar from the JDK and my ant task ran successfully

User · Answer

Check whether u have jdk installed in the path  C  Program Files Java   If not Install the JDK in your machine In Eclipse  right click on  build xml  then select Run As   External Tools Configuration Click on  JRE  tab then click on  Installed JREs     ADD     Standard VM    Click  Next  Select the Directory  C  Program Files Java jdk1 7 x xx  and the directory will be added to the  installed jres  Select the new JDK directory and Click  OK  Click on  Seperate JRE  dropdown and select the JDK version  jdk1 7 x xx  and click on  Run    This would help

User · Answer

I run into the same problem  Then I went into Run as -  Ant build   - jre  I found the jre used is separate JRE which is the default eclipse JRE 1 6   Then I went to the perferences - installed JREs   And change the location of the default eclipse JRE to my jdk 1 7    The problem is resolved

User · Answer

In my case  the project was a Maven  I had JDK 1 8 0  Eclipse   Kepler  and I installed the M2Eclipse plugin from Eclipse Marketplace   Changing compiler level didn t help   Finally I used latest version of eclipse  Luna   compiler level 1 7  same M2Eclipse plugin and problem was solved

User · Answer

The runtime jre was set to jre 6 instead of jre 7 in the build configuration window

[java] Why is Ant giving me a Unsupported major.minor version error

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