ProGuard says Unsupported class version number [52.0] (maximum 51.0, Java 1.7) with sbt-proguard

问题:

I'm on Mac OS X 10.9.2 and sbt 0.13.3-SNAPSHOT (built from the sources), Java 8 and sbt-proguard 0.2.2 plugin.

sbt 0.13.3-SNAPSHOT

[jacek]> sbtVersion [info] 0.13.3-SNAPSHOT 

Java 8

$ /Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home/bin/java -version java version "1.8.0" Java(TM) SE Runtime Environment (build 1.8.0-b132) Java HotSpot(TM) 64-Bit Server VM (build 25.0-b70, mixed mode) 

project/plugins.sbt

addSbtPlugin("com.typesafe.sbt" % "sbt-proguard" % "0.2.2") 

When I ran proguard:proguard in sbt shell it blew up with the following exception:

[sbt-updates]> show proguard:proguard [info] ProGuard, version 4.9 [info] Reading program directory [/Users/jacek/oss/sbt-updates/target/scala-2.10/sbt-0.13/classes] (filtered) [info] Reading program jar [/Users/jacek/.ivy2/cache/org.scalaz/scalaz-concurrent_2.10/bundles/scalaz-concurrent_2.10-7.1.0-M6.jar] (filtered) [info] Reading program jar [/Users/jacek/.sbt/boot/scala-2.10.3/lib/scala-library.jar] (filtered) [info] Reading program jar [/Users/jacek/.ivy2/cache/org.scalaz/scalaz-core_2.10/bundles/scalaz-core_2.10-7.1.0-M6.jar] (filtered) [info] Reading program jar [/Users/jacek/.ivy2/cache/org.scalaz/scalaz-effect_2.10/bundles/scalaz-effect_2.10-7.1.0-M6.jar] (filtered) [info] Reading library jar [/Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home/jre/lib/rt.jar] [error] Error: Can't read [/Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home/jre/lib/rt.jar] (Can't process class [apple/applescript/AppleScriptEngine.class] (Unsupported class version number [52.0] (maximum 51.0, Java 1.7))) [trace] Stack trace suppressed: run last proguard:proguard for the full output. [error] (proguard:proguard) Proguard failed with exit code [1] [error] Total time: 16 s, completed Apr 19, 2014 2:27:56 PM 

Why could be the reason for the error?

回答1:

It appears that ProGuard and hence sbt-proguard don't support Java 8 yet and changing the version of Java used in the script to launch sbt helped.

[sbt-updates]> show proguard:proguard [info] Compiling 8 Scala sources to /Users/jacek/oss/sbt-updates/target/scala-2.10/sbt-0.13/classes... [warn] there were 6 feature warning(s); re-run with -feature for details [warn] one warning found [info] ProGuard, version 4.9 [info] Reading program directory [/Users/jacek/oss/sbt-updates/target/scala-2.10/sbt-0.13/classes] (filtered) [info] Reading program jar [/Users/jacek/.ivy2/cache/org.scalaz/scalaz-concurrent_2.10/bundles/scalaz-concurrent_2.10-7.1.0-M6.jar] (filtered) ... 

This is with the following version of Java 7:

$ /Library/Java/JavaVirtualMachines/jdk1.7.0_51.jdk/Contents/Home/bin/java -version java version "1.7.0_51" Java(TM) SE Runtime Environment (build 1.7.0_51-b13) Java HotSpot(TM) 64-Bit Server VM (build 24.51-b03, mixed mode) 

回答2:

It's possible to update the version of Proguard that sbt-proguard uses by changing the key proguardVersion in build.sbt to a setting newer than 5.0, e.g.

ProguardKeys.proguardVersion in Proguard := "5.2.1" 

See: https://github.com/sbt/sbt-proguard/issues/5

文章来源: ProGuard says Unsupported class version number [52.0] (maximum 51.0, Java 1.7) with sbt-proguard