I needed to read a whole bunch of files recently and instead of just grabbing my old FileUtils.java that I and probably most developers have and then copy from project to project, I decided to have quick look at how else to do it…
Yes, I know there is Commons IO and Google IO, why would I even bother? They probably do it better, but I wanted to check out the NIO jdk classes and play with lambdas as well…and to be honest, I think this actually ended up being a very neat bit of code.
So I had a specific use case:
I wanted to read all the source files from a whole directory tree, line by line.
What this code does, it uses Files.walk to recursively get all the paths from the starting point, it creates a stream, which I then filter to only files that end with the required extension. For each of those files, I use Files.lines to create a stream of Strings, one per line. I trim that, filter out the empty ones and add them to the return collection.
All very concise thanks to the new constructs.
package net.briandupreez.blog.java8.io;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.FileVisitOption;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;
/**
* RecursiveFileLineReader
* Created by Brian on 2014-05-26.
*/
public class RecursiveFileLineReader {
private transient static final Log LOG = LogFactory.getLog(RecursiveFileLineReader.class);
/**
* Get all the non empty lines from all the files with the specific extension, recursively.
*
* @param path the path to start recursion
* @param extension the file extension
* @return list of lines
*/
public static List<String> readAllLineFromAllFilesRecursively(final String path, final String extension) {
final List<String> lines = new ArrayList<>();
try (final Stream<Path> pathStream = Files.walk(Paths.get(path), FileVisitOption.FOLLOW_LINKS)) {
pathStream
.filter((p) -> !p.toFile().isDirectory() && p.toFile().getAbsolutePath().endsWith(extension))
.forEach(p -> fileLinesToList(p, lines));
} catch (final IOException e) {
LOG.error(e.getMessage(), e);
}
return lines;
}
private static void fileLinesToList(final Path file, final List<String> lines) {
try (Stream<String> stream = Files.lines(file, Charset.defaultCharset())) {
stream
.map(String::trim)
.filter(s -> !s.isEmpty())
.forEach(lines::add);
} catch (final IOException e) {
LOG.error(e.getMessage(), e);
}
}
}| Reference: | Playing with Java 8 – Lambdas, Paths and Files from our JCG partner Brian Du Preez at the Zen in the art of IT blog. |
