RFR: 8277412: Use String.isBlank to simplify code in sun.net.www.protocol.mailto.Handler

[Andrey Turbanov]

On Tue, 7 Dec 2021 08:07:22 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> All this manually written code actually can be replaced with single String.isBlank() call.
>> `file` variable is guaranteed to be non-null.
>
> src/java.base/share/classes/sun/net/www/protocol/mailto/Handler.java line 125:
> 
>> 123:          * Let's just make sure we DO have an Email address in the URL.
>> 124:          */
>> 125:         if (file.isBlank())
> 
> The mail protocol handler is a legacy protocol handler and I don't know if there is good test coverage. The change proposed here changes the exception from RuntimeException to NPE when there isn't a file component in the URL. Neither is specified by URLStreamHandler.parseURL so I suspect there may be follow-on issues to clarify the spec on several points.

`file` can't be `null` here.  It's either empty string, or result of String.substring (which is also guarantee to be non-null).
Check code before this line:
https://github.com/openjdk/jdk/blob/07669e3bc65b1728d784e21ec83b437374f9fa19/src/java.base/share/classes/sun/net/www/protocol/mailto/Handler.java#L121-L125

IDEA confirms that
![изображение](https://user-images.githubusercontent.com/741251/145016751-a8a2b3b9-f286-4227-a30c-848a6446b48c.png)

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PR: https://git.openjdk.java.net/jdk/pull/6372