JDK-8172146 : If custom manifest contains "Multi-release: true" regular jar becomes MR jar
  • Type: Bug
  • Component: tools
  • Sub-Component: jar
  • Affected Version: 9
  • Priority: P3
  • Status: Closed
  • Resolution: Not an Issue
  • Submitted: 2016-12-30
  • Updated: 2017-01-09
  • Resolved: 2017-01-09
Related Reports
Relates :  
JDK-8071566 - Improve testing for multi-version JAR file maker tool
Description
To reproduce create manifest.txt with content
Multi-release: true

then create jar
$jar cfm test.jar manifest.txt  .

java.util.jar.JarFile.isMultiRelease will return true for the jar.
Comments
A Mr.JAR is identified by the manifest main attribute: Multi-Release: true A developer can, if they want, bypass the specific support for multi-release (including validation) and assemble in this manner (with or without explicit versioned directories). I would not recommend this approach but i don't think we should disallow it.
09-01-2017