RFR: 8345249: Apply some conservative cleanups in FileURLConnection

[Eirik Bjørsnøs]

On Fri, 29 Nov 2024 16:13:42 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Please review this PR which applies various cleanups to `sun.net.www.protocol.file.FileURLConnection`.
>> 
>> This class is known to be an _old, intricate, and hard to maintain piece of code._  However, there are some relatively straightforward refactorings / cleanups possible which improve readability and makes it easier to reason about what's going on in this class.
>> 
>> In this PR, I have chosen to make each individual small change a separate commit. This to assist review of each individual change, which can otherwise disappear a bit when reviewing the PR as a whole. 
>> 
>> A detailed listing of each commit follows in a separate comment.
>> 
>> This is a pure cleanup PR, no tests are added or updated in this PR.
>
> src/java.base/share/classes/sun/net/www/protocol/file/FileURLConnection.java line 78:
> 
>> 76:                 if (fileList == null)
>> 77:                     throw new FileNotFoundException(file.getPath() + " exists, but is not accessible");
>> 78:                 directoryListing = Arrays.<String>asList(fileList);
> 
> Is the `<String>` parameterization necessary? I tested on jshell, and it seems since the destination variable's type is `List<String>` we don't need this explicit parameterization to distinguish varargs.

Yes, indeed this can be dropped. See 06b2a23.

> src/java.base/share/classes/sun/net/www/protocol/file/FileURLConnection.java line 193:
> 
>> 191:                     String fileName = directoryListing.get(i);
>> 192:                     sb.append(fileName);
>> 193:                     sb.append("\n");
> 
> We can use a `StringJoiner` or stream to join the strings instead. (Note there is a suffix `\n` in the strings)

`StringJoiner` will not include the trailing line break. I want to be conservative in this PR so reluctant to introduce streams for this.

Opted to use an enhanced for-loop. See f9efa3b.

EDIT: Aha, `StringJoiner`, not `String.join` :-)  Still, I think I prefer keeping the explicit iteration for this PR.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22459#discussion_r1863827672
PR Review Comment: https://git.openjdk.org/jdk/pull/22459#discussion_r1863827700