What version of javac built my jar

Question

How can I tell what version of the Java compiler was used to build a jar   I have a jar file  and it could have been built in any one of three JDKs   We need to know exactly which one  so we can certify compatibility   Is the compiler version embedded somewhere in the class files or jar

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There is no need to unpack the JAR  if one of the class names is known or is looked up e g  using 7zip   so on Windows the following would be sufficient   javap -cp log4j-core-2 5 jar -verbose org apache logging log4j core Logger   findstr major

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Since I needed to analyze fat jars I was interested in the version of each individual class in a jar file  Therefore I took Joe Liversedge approach  https   stackoverflow com a 27877215 1497139 and combined it with David J  Liszewski  https   stackoverflow com a 3313839 1497139 class number version table to create a bash script jarv to show the versions of all class files in a jar file   usage  usage    jarv jarfile  -h --help  show this usage   Example  jarv  Home  m2 repository log4j log4j 1 2 17 log4j-1 2 17 jar  java 1 4 org apache log4j Appender java 1 4 org apache log4j AppenderSkeleton java 1 4 org apache log4j AsyncAppender DiscardSummary java 1 4 org apache log4j AsyncAppender Dispatcher       Bash script jarv     bin bash   WF 2018-07-12   find out the class versions with in jar file   see https   stackoverflow com questions 3313532 what-version-of-javac-built-my-jar    uncomment do debug   set -x   ansi colors  http   www csc uvic ca  sae seng265 fall04 tips s265s047-tips bash-using-colors html blue   033 0 34m    red   033 0 31m    green   033 0 32m      e 1 32m  is too bright for white bg  endColor   033 0m       a colored message      params        1  l color - the color of the message       2  l msg - the message to display   color msg       local l color   1    local l msg   2    echo -e    l color  l msg  endColor          error       show an error message and exit       params        1  l msg - the message to display error       local l msg   1      use ansi red for error   color msg  red  Error   l msg  1 gt  amp 2   exit 1        show the usage   usage       echo  usage   0 jarfile      -h --help usage show this usage   echo   -h --help  show this usage    exit 1         showclassversions   showclassversions       local l jar   1    jar -tf   l jar    grep   class    while read classname   do     class   echo  classname   sed -e  s   class          class version   javap -classpath   l jar  -verbose  class   grep  major version    cut -f2 -d       cut -c2-      class pretty   echo  class   sed -e  s     g       case  class version in       45 3  java version  java 1 1          46  java version  java 1 2          47  java version  java 1 3          48  java version  java 1 4          49  java version  java5          50  java version  java6          51  java version  java7          52  java version  java8          53  java version  java9          54  java version  java10             java version  x  class version x        esac     echo  java version  class pretty   done      check the number of parameters if      -lt 1   then   usage fi    start of script   check arguments while test    -gt 0 do   case  1 in       -h --help usage show this usage     -h --help         usage       exit 1                      showclassversions   1    esac   shift done

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A good deal of times  you might be looking at whole jar files  or war files that contain many jar files in addition to themselves   Because I didn t want to hand check each class  I wrote a java program to do that   https   github com Nthalk WhatJDK    whatjdk some war some war WEB-INF lib xml-apis-1 4 01 jar contains classes compatible with Java1 1 some war contains classes compatible with Java1 6   While this doesn t say what the class was compiled WITH  it determines what JDK s will be able to LOAD the classes  which is probably what you wanted to begin with

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Each class file has a version number embedded for the byte code level which the JVM use to see if it likes that particular byte code chunk or not   This is 48 for Java 1 4  49 for Java 1 5 and 50 for Java 6   Many compilers exist which can generate byte code at each level  javac uses the  -target  option to indicate which byte code level to generate  and the Java 6 javac can generate byte code for at least 1 4  1 5 and 6   I do not believe that the compiler inserts anything that can identify the compiler itself which is what I think you ask for   Also the Eclipse compiler is increasingly being used  as it is a single jar which can run with the JRE only   In a jar file there is usually many classes  and each of them is independent  so you need to investigate all classes in the jar to be certain about the characteristics of the contents

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Developers and administrators running Bash may find these convenience functions helpful   jar jdk version          -n   1   amp  amp  -x   command -v javap       amp  amp  javap -classpath   1  -verbose   jar -tf   1    grep   class    head -n1   sed -e  s   class        grep  major version    sed -e  s   0-9   1          print jar jdk version       local version   version   jar jdk version   1     case  version in 49  version 1 5   50  version 1 6   51  version 1 7   52  version 1 8   esac      -n   version      amp  amp  echo   basename   1   contains classes compiled with JDK version  version       You can paste them in for one-time usage or add them to    bash aliases or    bashrc  The results look something like     jar jdk version poi-ooxml-3 5-FINAL jar 49   and    print jar jdk version poi-ooxml-3 5-FINAL jar poi-ooxml-3 5-FINAL jar contains classes compiled with JDK version 1 5    EDIT As jackrabbit points out  you can t 100  rely on the manifest to tell you anything useful  If it was  then you could pull it out in your favorite UNIX shell with unzip     unzip -pa poi-ooxml-3 5-FINAL jar META-INF MANIFEST MF Manifest-Version  1 0 Ant-Version  Apache Ant 1 7 1 Created-By  11 3-b02  Sun Microsystems Inc   Built-By  yegor Specification-Title  Apache POI Specification-Version  3 5-FINAL-20090928 Specification-Vendor  Apache Implementation-Title  Apache POI Implementation-Version  3 5-FINAL-20090928 Implementation-Vendor  Apache   This  jar doesn t have anything useful in the manifest about the contained classes

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Here is Java s way to find this information   Windows  javap -v  lt class gt    findstr major Unix  javap -v  lt class gt    grep major   For example   gt  javap -v Application   findstr major  nbsp  nbsp major version  51

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you can find Java compiler version from  class files using a Hex Editor   Step 1  Extract  class files from jar file using a zip extractor  step 2  open  class file with a hex editor  I have used notepad   hex editor plugin  This plugin reads file as binary and shows it in hex  You can see below     Index 6 and 7 gives major version number of the class file format being used  https   en wikipedia org wiki Java class file  Java SE 11   55  0x37 hex   Java SE 10   54  0x36 hex   Java SE 9   53  0x35 hex   Java SE 8   52  0x34 hex    Java SE 7   51  0x33 hex    Java SE 6 0   50  0x32 hex    Java SE 5 0   49  0x31 hex    JDK 1 4   48  0x30 hex    JDK 1 3   47  0x2F hex    JDK 1 2   46  0x2E hex    JDK 1 1   45  0x2D hex

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The Java compiler  javac  does not build jars  it translates Java files into class files  The Jar tool  jar  creates the actual jars  If no custom manifest was specified  the default manifest will specify which version of the JDK was used to create the jar

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You can t tell from the JAR file itself  necessarily   Download a hex editor and open one of the class files inside the JAR and look at byte offsets 4 through 7   The version information is built in   http   en wikipedia org wiki Java class file  Note  As mentioned in the comment below       those bytes tell you what version the class has been compiled FOR  not   what version compiled it

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On Windows do the following    Unzip or extract the JAR file using WinZip   Java JAR command  Drag and Drop one of the class files into your Eclipse Java project  Open the class file    Now Eclipse will show the exact major and minor version

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To expand on Jonathon Faust s and McDowell s answers  If you re on a  nix based system  you can use od  one of the earliest Unix programs1 which should be available practically everywhere  to query the  class file on a binary level   od -An -j7 -N1 -t dC SomeClassFile class   This will output the familiar integer values  e g  50 for Java 5  51 for Java 6 and so on   1 Quote from https   en wikipedia org wiki Od  Unix

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The code posted by Owen can tell you the information mentioned by a number of the other answers here   public void simpleExample          FileInputStream fis   new FileInputStream   mytest class        parseJavaClassFile   fis      protected void parseJavaClassFile   InputStream classByteStream   throws Exception       DataInputStream dataInputStream   new DataInputStream   classByteStream        magicNumber   dataInputStream readInt        if   magicNumber    0xCAFEBABE                 int minorVer   dataInputStream readUnsignedShort            int majorVer   dataInputStream readUnsignedShort               do something here with major  amp  minor numbers           See also this and this site  I ended up modifying the Mind Products code quickly to check what each of my dependencies was compiled for

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You check in Manifest file of jar example   Manifest-Version  1 0 Created-By  1 6 0  IBM Corporation

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I as well wrote my own bash script to dump the Java version required by all the jars passed at the command line    Mine is a bit rough  but works for me  -   example usage    jar dump version of jvm required sh   jar JVM VERSION REQUIRED  46 0   private tmp jars WEB-INF lib json-simple-1 1 jar JVM VERSION REQUIRED  49 0   private tmp jars WEB-INF lib json-smart-1 1 1 jar JVM VERSION REQUIRED  50 0   private tmp jars WEB-INF lib jsontoken-1 0 jar JVM VERSION REQUIRED  50 0   private tmp jars WEB-INF lib jsr166y-1 7 0 jar   jar dump version of jvm required sh     bin bash  DIR   PWD  function show help       ME   basename  0    IT   cat  lt  lt EOF    Dumps the version of the JVM required to run the classes in a jar file    usage   ME JAR FILE    e g       ME myFile jar    - gt   VERSION  50 0     myFile jar    Java versions are    54   Java 10   53   Java 9   52   Java 8   51   Java 7   50   Java 6   49   Java 5   48   Java 1 4   47   Java 1 3   46   Java 1 2   45 3   Java 1 1  EOF       echo   IT    exit    if     1      help    then   show help fi if   -z   1    then   show help fi  function unzipJarToTmp       JAR  1   CLASS FILE   jar -tf   JAR    grep   class    grep -v        head -n1   awk   print  NF      OUT FILE   CLASS FILE     echo  J  JAR C  CLASS FILE O  OUT FILE    jar xf   JAR    CLASS FILE     MAJOR   javap -v   OUT FILE  2 gt  amp 1   grep major   awk -F      print  3      MINOR   javap -v   OUT FILE  2 gt  amp 1   grep minor   awk -F      print  3      if   -z   MAJOR      then     echo  JVM VERSION REQUIRED  NA as no classes in  JAR    else     echo  JVM VERSION REQUIRED   MAJOR  MINOR   JAR    fi      loop over cmd line args for JAR in      do   cd   DIR    JAR UID   basename   JAR    sed s  jar  g    TMPDIR  tmp jar dump  JAR UID    mkdir -p   TMPDIR    JAR ABS PATH   realpath  JAR     cd   TMPDIR      echo   JAR ABS PATH    unzipJarToTmp   JAR ABS PATH     sleep 2 done

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I build a little bash script  on github  based on Davids suggestion using the file command

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One liner  Linux   unzip -p mylib jar META-INF MANIFEST MF  This prints the content of MANIFEST MF file to stdout  hopefully there is one in your jar file     Depending on what built your package  you will find the JDK version in Created-By or Build-Jdk key

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You can tell the Java binary version by inspecting the first 8 bytes  or using an app that can    The compiler itself doesn t  to the best of my knowledge  insert any identifying signature  I can t spot such a thing in the file VM spec class format anyway

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Following up on  David J  Liszewski s answer  I ran the following commands to extract the jar file s manifest on Ubuntu     Determine the manifest file name    jar tf LuceneSearch jar   grep -i manifest META-INF MANIFEST MF    Extract the file    sudo jar xf LuceneSearch jar META-INF MANIFEST MF    Print the file s contents    more META-INF MANIFEST MF Manifest-Version  1 0 Ant-Version  Apache Ant 1 8 2 Created-By  1 7 0 25-b30  Oracle Corporation  Main-Class  org wikimedia lsearch config StartupManager

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A jar is merely a container  It is a file archive a la tar  While a jar may have interesting information contained within it s META-INF hierarchy  it has no obligation to specify the vintage of the classes within it s contents  For that  one must examine the class files therein  As as Peter Lawrey mentioned in comment to the original question  you can t necessarily know which JDK release built a given class file  but you can find out the byte code class version of the class file contained in a jar  Yes  this kinda sucks  but the first step is to extract one or more classes from the jar  For example    jar xf log4j-1 2 15 jar  On Linux  Mac OS X or Windows with Cygwin installed  the file 1  command knows the class version    file   org apache log4j Appender class   org apache log4j Appender class  compiled Java class data  version 45 3  Or alternatively  using javap from the JDK as  jikes thunderbolt aptly points out    javap -v   org apache log4j Appender class   grep major  major version  45  For Windows environments without either file or grep  gt  javap -v   org apache log4j Appender class   findstr major  major version  45  FWIW  I will concur that javap will tell a whole lot more about a given class file than the original question asked  Anyway  a different class version  for example    file   bin classes P class  home dave bin classes P class  compiled Java class data  version 50 0  The class version major number corresponds to the following Java JDK versions   45 3   Java 1 1 46   Java 1 2 47   Java 1 3 48   Java 1 4 49   Java 5 50   Java 6 51   Java 7 52   Java 8 53   Java 9 54   Java 10 55   Java 11 56   Java 12 57   Java 13 58   Java 14

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You can easily do this on command line using following process    If you know any of the class name in jar  you can use following command    javap -cp jarname jar -verbose packagename classname   findstr major   example        C  pathwherejarlocated gt  javap -cp jackson-databind-2 8 6 jar -verbose com fasterxml jackson databind JsonMappingException   findstr major   Output        major version  51   Quick Reference    JDK 1 0     major version 45  DK 1 1     major version 45  JDK 1 2     major version 46  JDK 1 3     major version 47  JDK 1 4     major version 48  JDK 1 5     major version 49  JDK 1 6     major version 50  JDK 1 7     major version 51  JDK 1 8     major version 52  JDK 1 9     major version 53       PS   if you dont know any of the classname   you can easily do this by   using any of the jar decompilers or by simply using following command to extract jar file      jar xf myFile jar

[java] What version of javac built my jar?

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