Streams from Files

Description

java.io and java.nio.file packages from Java 8 has added many methods to support I/O operations using streams.

We can read text from a file as a stream of strings. Each element in the stream represents one line of text.

We can also use a stream to read JarEntry from a JarFile and we can read entries in a directory as a stream of Path.

Auto close

Calling the close() method on the stream will close the underlying file.

Alternatively, we can create the stream in a try-with-resources statement so the underlying file is closed automatically.

Example

The following code shows how to read contents of a file using a stream.


import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.stream.Stream;
/* ww  w . j av a2s .com*/
public class Main {
  public static void main(String[] args) {
    Path path = Paths.get("./Main.java");
    try (Stream<String> lines = Files.lines(path)) {
      lines.forEach(System.out::println);
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

The code above generates the following result.

Example 2

The following code shows how to read a path using stream.


import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.stream.Stream;
//  w w  w  .  j  a  va2 s.  co  m
public class Main {
  public static void main(String[] args) {
    Path dir = Paths.get(".");
    System.out.printf("%nThe file tree for %s%n", 
        dir.toAbsolutePath());
    try (Stream<Path> fileTree = Files.walk(dir)) {
      fileTree.forEach(System.out::println);
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}