RFR: 8354724: Methods in java.io.Reader to read all characters and all lines [v19]

[Markus KARG]

On Tue, 13 May 2025 15:33:39 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Implement the requested methods and add a test thereof.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8354724: "stream" -> "reader"

src/java.base/share/classes/java/io/Reader.java line 205:

> 203:             public String readAllAsString() throws IOException {
> 204:                 ensureOpen();
> 205:                 String result = cs.toString().substring(next);

For sake of efficiency can we please *first* limit and copy *last*? If `cs` refers to a huge object and `next` is just few bytes before `length()`, it makes no sense to copy the huge memory block just to return one or two characters finally. 🤔 

`result = cs.subSequence(next, cs.length()).toString()`?

src/java.base/share/classes/java/io/Reader.java line 500:

> 498:      * @since 25
> 499:      */
> 500:     public String readAllAsString() throws IOException {

Still thinking that declaring `CharSequence` instead of `String` would be beneficial. In case a `Reader` implementation reads from I/O, the implementation could so return a block of native memory without turning it into a Java `String` just for sake of fulfilling the API. In case of servers for example, the information often is passed-through from one I/O source to another I/O sink *unmodified*, which means, the `String` then is turned into *a new* native memory block again; double native memory used *plus* on-heap memory used, without any benefit. Can we please provide I/O APIs which do *not* enforce duplicate copying to and from `String` in such scenarios? 😃

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PR Review Comment: https://git.openjdk.org/jdk/pull/24728#discussion_r2089421861
PR Review Comment: https://git.openjdk.org/jdk/pull/24728#discussion_r2089436642