Multi-release jar file - Should the "Multi-Release" mainfest attribute have a specific value?

Jaikiran Pai jai.forums2013 at
Thu Jan 24 03:12:59 UTC 2019

Thank you Alan.


On 23/01/19 8:09 PM, Alan Bateman wrote:
> On 23/01/2019 14:27, Jaikiran Pai wrote:
>> Hi,
>> The Multi-Release JarFile support JEP[1] notes that the jar file is
>> expected to contain a main attribute:
>> Multi-Release: true
>> The JarFile javadoc[1] on the other hand makes no mention of the value
>> for such an attribute and just mentions that the Multi-Release main
>> attribute needs to be present:
>> "A multi-release jar file is a jar file that contains a manifest with a
>> main attribute named "Multi-Release",..."
>> Which one of these 2 docs is expected to be the formal specification?
>> I'm guessing it's the javadoc, in which case, is it intentional that the
>> value for this attribute isn't mentioned or is it just a miss? My quick
>> tests show that the implementation of this feature does indeed expect
>> the value to be a "true" for it to consider the versioned entries in a
>> multi-release jar.
> The JAR file spec [1] is the specification. There's a lengthy section
> defining MR JARs. The API docs are also specification, for the APIs
> that provide access to JAR files, including MR JARs. So yes, you need
> the "Multi-Release" attribute in the main section of the JAR file
> manifest and it needs to have a value of "true" to enable. There is
> also a JDK-specific property, documented in the JarFile docs, to
> override the configuration where needed.
> -Alan
> [1]

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