FULL PRODUCT VERSION :
java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)
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ADDITIONAL OS VERSION INFORMATION :
Linux artemis 4.9.13-101.fc24.x86_64 #1 SMP Tue Mar 7 23:48:32 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
A plain HttpUrlConnection created like this:

URL url = new URL("http", "localhost", 8888, "/");
URLConnection conn = url.openConnection();
conn.getInputStream();

Sends a request with a header line:

    Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2

In this list of media ranges, the media range "*; q=.2" is illegal. RFC 7231, section 5.3.2 defines a media range as

media-range = ( "*/*"
                      / ( type "/" "*" )
                      / ( type "/" subtype )
                      ) *( OWS ";" OWS parameter )

So the part without the parameter must be

                      ( "*/*"
                      / ( type "/" "*" )
                      / ( type "/" subtype )

This obviously does not include "*".

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the program above, use e.g. wireshark to get the header sent.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
An RFC compliant header.
ACTUAL -
See above.

REPRODUCIBILITY :
This bug can be reproduced always.

CUSTOMER SUBMITTED WORKAROUND :
Explicitly set the accept range, e.g.:

URLConnection conn = url.openConnection();
// URLConnection default accept header is illegal
conn.setRequestProperty("Accept", "*/*");