How to update ProGuard for Android SDK

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.

1. Move / rename the old version:

   rename \android-sdk\tools\proguard\ proguard.old

2. Download the zip file from SourceForce
    
3. Extract the contents into \android-sdk\tools\ renaming the new folder to proguard

   rename \android-sdk\tools\proguard5.3.3\ proguard

4. Check the new version:

   > cd \android-sdk\tools\proguard\bin\
   > proguard
   ProGuard, version 5.3.3
   Usage: java proguard.ProGuard [options ...]

5. 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.