> On 15 Apr 2025, at 07:52, Cay Horstmann <cay.horstm...@gmail.com> wrote:
>
>
>
> Il 14/04/25 23:46, Ron Pressler ha scritto:
>>> On 14 Apr 2025, at 21:48, Remi Forax <fo...@univ-mlv.fr> wrote:
>>>
>>>
>>> Hi Ron,
>>> i think you need to close the inputReader
>>>
>>> public static String output(String... args) {
>>> ProcessBuilder processBuilder = new ProcessBuilder(args);
>>> try {
>>> Process process = processBuilder.start();
>>> try (BufferedReader reader = process.inputReader()) {
>>> return reader.lines().collect(Collectors.joining("\n"));
>>> }
>>> } catch (IOException e) {
>>> throw new IOError(e);
>>> }
>>> }
>> When the process terminates, the InputStream underlying the pipe is closed
>> (after being drained and the unread bytes served by a ByteArrayInputStream),
>> which *I think* should be sufficient, but I could be wrong.
>> — Ron
>
> Reading the process output into a string or string stream raises a number of
> worries.
>
> * Do I need to wait for the process to complete?
I don’t know all the error conditions, but since you’re reading the stream
until its end, and this pipe ends when the process closes, then I don’t think
you need to also wait for the process complete, but you may want to call
waitFor to get the exit status.
> * Do I need to close anything?
It seems to me that all the pipes are closed when the process ends, so no, but
I’m not an expert in this area.
> * How exactly do I use getInputStream()/inputReader() with *extreme care*, as
> the API doc warns me?
I think that note cautions that if you want to use that pair of methods
*together*, then be careful because they’re both reading from the same
underlying stream.
>
> If it is safe to call
>
> builder.start().inputReader().lines()
>
> or
>
> builder.start().getInputStream().readAllBytes()
>
> without waiting or closing, then the API doc could say so.
I think so, and so I guess the doc should say that, but there could be error
conditions that complicate matters (e.g. what happens if your thread is
interrupted?)
> If not, then maybe a safe method to get the entire output would be
> appropriate for Process?
>
In what form, though? A Stream<String> of lines seems the most flexible and
convenient — calling .toList() on it seems especially convenient.
But perhaps that hypothetical Process.inputLines() method could also have the
returned Stream<String> throw an exception if the process terminates with a
non-zero code, making things even more convenient, like so:
var p = new ProcessBuilder("ls", "-al").start();
try {
var lines = p.inputLines().toList();
...
} catch (ProcessFailedException ex) {
var errorLines = p.errorLines().toList();
...
}
— Ron
