RFR: 8345249: Apply some conservative cleanups in FileURLConnection

[Chen Liang]

On Fri, 29 Nov 2024 13:33:37 GMT, Eirik Bjørsnøs <eirbjo 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.

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)

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PR Review Comment: https://git.openjdk.org/jdk/pull/22459#discussion_r1863735620
PR Review Comment: https://git.openjdk.org/jdk/pull/22459#discussion_r1863738691