RFR: 8320577: Improve MessageHeader's toString() function to make HttpURLConnection's debug log readable

[Oliver Lockwood]

On Wed, 22 Nov 2023 08:49:12 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

>> At the moment, if you have debug logging turned on for the `HttpURLConnection` class, then from [line 746](https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/sun/net/www/protocol/http/HttpURLConnection.java#L746) a log message like this is generated:
>>> sun.net.www.MessageHeader at 49c4f2906 pairs: {null: HTTP/1.1 200}{Content-Type: application/json}{Transfer-Encoding: chunked}{Date: Thu, 09 Nov 2023 11:50:00 GMT}{Keep-Alive: timeout=60}{Connection: keep-alive}
>> 
>> The lack of separation after the `Object.toString()` output makes it hard to realise from the above that it's trying to say "6 pairs". 
>> The change proposed by this PR would make the same log operation output this, instead:
>>> sun.net.www.MessageHeader at 49c4f290 6 pairs: {null: HTTP/1.1 200}{Content-Type: application/json}{Transfer-Encoding: chunked}{Date: Thu, 09 Nov 2023 11:50:00 GMT}{Keep-Alive: timeout=60}{Connection: keep-alive}
>
> Hi @oliverlockwood all PRs need to be associated to a Java Bug System ticket; I created one for you. Please change the PR title to `8320577` to mark this PR as ready for review.

Hi @djelinski, thank you for taking the time to do this on my behalf.  I have now formed the title to be like `issue number: message` as per the check and other open PRs that I can see.  Please let me know if you need me to jump through any other hurdles 😄

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PR Comment: https://git.openjdk.org/jdk/pull/16615#issuecomment-1822389833