LineCounter.java

package uk.kludje.test.sample;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Collection;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import static java.nio.charset.StandardCharsets.UTF_8;
import static uk.kludje.fn.function.UFunction.asUFunction;

/**
 * Line counter - stream approach with checked exception handling.
 */
public class LineCounter {

  public Map<Path, Long> countLines(Collection<? extends Path> paths) throws IOException {
    return paths.stream()
        .parallel()
        .collect(Collectors.<Path, Path, Long>toConcurrentMap(p -> p, asUFunction(this::linesIn)));
  }

  private long linesIn(Path path) throws IOException {
    try (Stream<String> lines = Files.lines(path, UTF_8)) {
      return lines.count();
    }
  }
}