[java] java.lang.UnsupportedClassVersionError Unsupported major.minor version 51.0

I am trying to build an application, but it gives some error. My JDK version is given below:

java version "1.6.0_30"
Java(TM) SE Runtime Environment (build 1.6.0_30-b12)
Java HotSpot(TM) Client VM (build 20.5-b03, mixed mode, sharing)

Here is my Error Log:

Buildfile: build.xml

compile:
     [echo] Compiling the service....
     [echo]   ...mkdir for classes first....
     [echo]   ...java classes next....
     [echo]   ...mkdir for generated code next....
     [echo]  ...generate stubs/skeletons next....
[wscompile] command line: wscompile -d /home/vivekray/program/MTrans/WEB-INF/classes -features:wsi,documentliteral -gen:server -keep -model /home/vivekray/program/MTrans/WEB-INF/model.gz -verbose -Xprintstacktrace /home/vivekray/program/MTrans/src/config.xml -classpath /home/vivekray/program/MTrans/WEB-INF:/home/vivekray/program/MTrans/WEB-INF/classes:/home/vivekray/program/MTrans/lib/log4j-1.2.16.jar:/home/vivekray/jwsdp-2.0/jwsdp-shared/lib/mail.jar:/home/vivekray/jwsdp-2.0/jwsdp-shared/lib/activation.jar:/home/vivekray/jwsdp-2.0/jaxp/lib/jaxp-api.jar:/home/vivekray/jwsdp-2.0/jaxp/lib/endorsed/dom.jar:/home/vivekray/jwsdp-2.0/jaxp/lib/endorsed/sax.jar:/home/vivekray/jwsdp-2.0/jaxp/lib/endorsed/xalan.jar:/home/vivekray/jwsdp-2.0/jaxp/lib/endorsed/xercesImpl.jar:/home/vivekray/jwsdp-2.0/jaxrpc/lib/jaxrpc-api.jar:/home/vivekray/jwsdp-2.0/jaxrpc/lib/jaxrpc-spi.jar:/home/vivekray/jwsdp-2.0/jaxrpc/lib/jaxrpc-impl.jar:/home/vivekray/jwsdp-2.0/saaj/lib/saaj-api.jar:/home/vivekray/jwsdp-2.0/saaj/lib/saaj-impl.jar:/home/vivekray/jwsdp-2.0/jwsdp-shared/lib/relaxngDatatype.jar:/home/vivekray/jwsdp-2.0/jwsdp-shared/lib/xsdlib.jar:/home/vivekray/jwsdp-2.0/jwsdp-shared/lib/jax-qname.jar:/home/vivekray/jwsdp-2.0/apache-ant/lib/ant.jar:/home/vivekray/jwsdp-2.0/fastinfoset/lib/FastInfoset.jar:/home/vivekray/Softwares/apache-tomcat-7.0.27/lib/servlet-api.jar
[wscompile] [creating model: mtransservice]
[wscompile] [creating service: Mtransservice]

BUILD FAILED
java.lang.UnsupportedClassVersionError: in/cdac/mobile/computing/mtrans/MtransService : Unsupported major.minor version 51.0
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
    at org.apache.tools.ant.AntClassLoader.defineClassFromData(AntClassLoader.java:1146)
    at org.apache.tools.ant.AntClassLoader.getClassFromStream(AntClassLoader.java:1324)
    at org.apache.tools.ant.AntClassLoader.findClassInComponents(AntClassLoader.java:1388)
    at org.apache.tools.ant.AntClassLoader.findClass(AntClassLoader.java:1341)
    at org.apache.tools.ant.AntClassLoader.loadClass(AntClassLoader.java:1088)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:295)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:247)
    at com.sun.xml.rpc.processor.modeler.rmi.RmiUtils.getLoadableClassName(RmiUtils.java:78)
    at com.sun.xml.rpc.processor.modeler.rmi.RmiUtils.getRealName(RmiUtils.java:54)
    at com.sun.xml.rpc.processor.modeler.rmi.RmiModeler.modelPort(RmiModeler.java:676)
    at com.sun.xml.rpc.processor.modeler.rmi.RmiModeler.buildLiteralModel(RmiModeler.java:603)
    at com.sun.xml.rpc.processor.modeler.rmi.RmiModeler.buildModel(RmiModeler.java:457)
    at com.sun.xml.rpc.processor.config.ModelInfo.buildModel(ModelInfo.java:88)
    at com.sun.xml.rpc.processor.Processor.runModeler(Processor.java:63)
    at com.sun.xml.rpc.tools.wscompile.CompileTool.run(CompileTool.java:714)
    at com.sun.xml.rpc.util.ToolBase.run(ToolBase.java:43)
    at com.sun.xml.rpc.tools.ant.Wscompile.execute(Wscompile.java:746)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:288)
    at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.apache.tools.ant.Task.perform(Task.java:348)
    at org.apache.tools.ant.Target.execute(Target.java:357)
    at org.apache.tools.ant.Target.performTasks(Target.java:385)
    at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1337)
    at org.apache.tools.ant.Project.executeTarget(Project.java:1306)
    at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
    at org.apache.tools.ant.Project.executeTargets(Project.java:1189)
    at org.apache.tools.ant.Main.runBuild(Main.java:758)
    at org.apache.tools.ant.Main.startAnt(Main.java:217)
    at org.apache.tools.ant.launch.Launcher.run(Launcher.java:257)
    at org.apache.tools.ant.launch.Launcher.main(Launcher.java:104)

Total time: 1 second

These guys gave you the reason why is failing but not how to solve it. This problem may appear even if you have a jdk which matches JVM which you are trying it into.

Project -> Properties -> Java Compiler

Enable project specific settings.

Then select Compiler Compliance Level to 1.6 or 1.5, build and test your app.

Now, it should be fine.

It means that you compiled your classes under a specific JDK, but then try to run them under older version of JDK.

Use Maven and use the maven-compiler-plugin to explicitly call the actual correct version JDK javac.exe command, because Maven could be running any version; this also catches the really stupid long standing bug in javac that does not spot runtime breaking class version jars and missing classes/methods/properties when compiling for earlier java versions! This later part could have easily been fixed in Java 1.5+ by adding versioning attributes to new classes, methods, and properties, or separate compiler versioning data, so is a quite stupid oversight by Sun and Oracle.

I encountered the same issue, when jdk 1.7 was used to compile then jre 1.4 was used for execution.

My solution was to set environment variable PATH by adding pathname C:\glassfish3\jdk7\bin in front of the existing PATH setting. The updated value is "C:\glassfish3\jdk7\bin;C:\Sun\SDK\bin". After the update, the problem was gone.

Version 51 is Java 7, you probably use the wrong JDK. Check JAVA_HOME.

As mentioned here, under Binary Compatibility

Make sure you're using the correct SDK when compiling/running and also, make sure you use source/target 1.7.