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

[Jaikiran Pai]

On Fri, 10 Nov 2023 14:23:19 GMT, Oliver Lockwood <duke 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}

Good catch. I've seen that log message in the log files a few times before and it never occurred to me that it was trying to say that there are "X" number of message header pairs.
Change looks good to me other than what Daniel already noted about the copyright year.

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Marked as reviewed by jpai (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16615#pullrequestreview-1744393055