Get content of a file inside a directory

Question

I want to get the content of a file inside a directory:

/sys/block/sda/device/model

I use this code to get the content:

String content = new String(Files.readAllBytes(Paths.get("/sys/block/sda/device/model")));

But in some scenarios, I have cases like this:

/sys/block/sda/device/model
/sys/block/sdb/device/model
/sys/block/sdc/device/model

How I can iterate all the directories starting with

sd* and print the file model?

Can you show me some example for Java 8 with filter?

I think there is backward links in the directory that you reading from. its just a hypothesis. can you check that? — nafas, Aug 01 '14 at 08:47
check on filters http://www.tutorialspoint.com/java/io/file_listfiles_file_filter.htm — Thusitha Thilina Dayaratne, Aug 01 '14 at 09:03
Can you check if this post helps? http://stackoverflow.com/questions/794381/how-to-find-files-that-match-a-wildcard-string-in-java — longhua, Aug 01 '14 at 09:03

score 2 · Accepted Answer · answered Aug 01 '14 at 15:03

Here is an example of how to do this using Java 8 features:

Function<Path,byte[]> uncheckedRead = p -> {
  try { return Files.readAllBytes(p); }
  catch(IOException ex) { throw new UncheckedIOException(ex); }
};
try(Stream<Path> s=Files.find(Paths.get("/sys/block"), 1,
    (p,a)->p.getName(p.getNameCount()-1).toString().startsWith("sd"))) {
  s.map(p->p.resolve("device/model")).map(uncheckedRead).map(String::new)
   .forEach(System.out::println);
}

This is an example that strives for compactness and working stand-alone. For real applications, it’s likely that you would do it a bit differently. The task of using an IO operation as a Function which doesn’t allow checked exception is quite common so you might have a wrapper function like:

interface IOFunction<T,R> {
    R apply(T in) throws IOException;
}
static <T,R> Function<T,R> wrap(IOFunction<T,R> f) {
    return t-> { try { return f.apply(t); }
      catch(IOException ex) { throw new UncheckedIOException(ex); }
    };
}

Then you can use

try(Stream<Path> s=Files.find(Paths.get("/sys/block"), 1,
    (p,a)->p.getName(p.getNameCount()-1).toString().startsWith("sd"))) {
  s.map(p->p.resolve("device/model")).map(wrap(Files::readAllBytes))
   .map(String::new).forEach(System.out::println);
}

But maybe you’d use newDirectoryStream instead even if the returned DirectoryStream is not a Stream and hence requires a manual Stream creation as this method allows passing a glob pattern like "sd*":

try(DirectoryStream<Path> ds
                     =Files.newDirectoryStream(Paths.get("/sys/block"), "sd*")) {
  StreamSupport.stream(ds.spliterator(), false)
    .map(p->p.resolve("device/model")).map(wrap(Files::readAllBytes))
    .map(String::new).forEach(System.out::println);
}

Finally, the option to process the files as stream of lines should be mentioned:

try(DirectoryStream<Path> ds
                     =Files.newDirectoryStream(Paths.get("/sys/block"), "sd*")) {
  StreamSupport.stream(ds.spliterator(), false)
    .map(p->p.resolve("device/model")).flatMap(wrap(Files::lines))
    .forEach(System.out::println);
}

prashant thakre · Answer 2 · 2014-08-01T09:58:03.727

1

Rather using st* it's better if you can first search the existing folder inside the path /sys/block by using below code.

Please find working example :-

String dirNames[] = new File("E://block").list();
for(String name : dirNames)
{
    if (new File("E://block//" + name).isDirectory())
    {
        if(name.contains("sd")){
            String content = new String(Files.readAllBytes(Paths.get("E://block//"+name+"//device//model")));
            System.out.println(content);
        }

    }
}

edited Aug 01 '14 at 09:58

answered Aug 01 '14 at 09:04

prashant thakre

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@PeterPenzov I have edited my answer to provide the full solution, I tested in my system and its working fine. – prashant thakre Aug 01 '14 at 09:58
By the way is this for Java 8? Is there other more optimized for performance way? – Peter Penzov Aug 01 '14 at 11:14
@Peter Penzov: no, besides your own `readAllBytes` part this code is not the slightest Java 8 related. Id doesn’t even uses Java 7 features. – Holger Aug 01 '14 at 12:00
Can you please show me how this code can be implemented with the new Java 8 features? – Peter Penzov Aug 01 '14 at 12:16

Get content of a file inside a directory

2 Answers2