If still using Eclipse for Android app development and targeting newer Android SDK versions you may find ProGuard failing with this error message:
Can't process class [junit/runner/Version.class] (Unsupported class version number [52.0] (maximum 51.0, Java 1.7))
Proguard returned with error code 1. See console
Proguard Error 1
Output:
java.io.IOException: Can't read [U:\Android\android-sdk\platforms\android-27\android.jar] (Can't process class [junit/runner/Version.class] (Unsupported class version number [52.0] (maximum 51.0, Java 1.7)))
at proguard.InputReader.readInput(InputReader.java:230)
at proguard.InputReader.readInput(InputReader.java:200)
at proguard.InputReader.readInput(InputReader.java:178)
at proguard.InputReader.execute(InputReader.java:100)
at proguard.ProGuard.readInput(ProGuard.java:196)
at proguard.ProGuard.execute(ProGuard.java:78)
at proguard.ProGuard.main(ProGuard.java:492)
Caused by: java.io.IOException: Can't process class [junit/runner/Version.class] (Unsupported class version number [52.0] (maximum 51.0, Java 1.7))
at proguard.io.ClassReader.read(ClassReader.java:112)
at proguard.io.FilteredDataEntryReader.read(FilteredDataEntryReader.java:87)
at proguard.io.JarReader.read(JarReader.java:65)
at proguard.io.DirectoryPump.readFiles(DirectoryPump.java:65)
at proguard.io.DirectoryPump.pumpDataEntries(DirectoryPump.java:53)
at proguard.InputReader.readInput(InputReader.java:226)
... 6 more
Caused by: java.lang.UnsupportedOperationException: Unsupported class version number [52.0] (maximum 51.0, Java 1.7)
at proguard.classfile.util.ClassUtil.checkVersionNumbers(ClassUtil.java:140)
at proguard.classfile.io.LibraryClassReader.visitLibraryClass(LibraryClassReader.java:89)
at proguard.classfile.LibraryClass.accept(LibraryClass.java:301)
at proguard.io.ClassReader.read(ClassReader.java:86)
... 11 more
Cause
Newer versions of Android platform are compiled as Java 8 binary and ProGuard 4.7 coming with Android SDK Tools doesn't support it (last updated with
SDK Tools Revision 17, March 2012).
> cd \android-sdk\tools\proguard\bin
> proguard
ProGuard, version 4.7
Usage: java proguard.ProGuard [options ...]
Solution
Java 8 support is available with
Proguard 5.x onwards, so we will update to the latest version available, in my case 5.3.3 from Apr 2017.
- Move / rename the old version:
rename \android-sdk\tools\proguard\ proguard.old
- Download the zip file from SourceForce
- Extract the contents into \android-sdk\tools\ renaming the new folder to proguard
rename \android-sdk\tools\proguard5.3.3\ proguard
- Check the new version:
> cd \android-sdk\tools\proguard\bin\
> proguard
ProGuard, version 5.3.3
Usage: java proguard.ProGuard [options ...]
- Copy the Android configuration files over:
> cd \android-sdk\tools\
> copy proguard.old\proguard-*.txt proguard\
proguard.old\proguard-android-optimize.txt
proguard.old\proguard-android.txt
proguard.old\proguard-project.txt
3 file(s) copied.
Exporting the APK package again should work now.
