How to read from files with Files.lines(…).forEach(…)?

Question

I'm currently trying to read lines from a text only file that I have. I found on another stackoverflow(Reading a plain text file in Java) that you can use Files.lines(..).forEach(..) However I can't actually figure out how to use the for each function to read line by line text, Anyone know where to look for that or how to do so?

Answer 1

Sample content of test.txt

Hello
Stack
Over
Flow
com

Code to read from this text file using lines() and forEach() methods.

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.stream.Stream;

public class FileLambda {

    public static void main(String JavaLatte[]) {
        Path path = Paths.get("/root/test.txt");
        try (Stream<String> lines = Files.lines(path)) {
            lines.forEach(s -> System.out.println(s));
        } catch (IOException ex) {
          // do something or re-throw...
        }
    }
}

Answer 2

With Java 8, if file exists in a classpath:

Files.lines(Paths.get(ClassLoader.getSystemResource("input.txt")
                    .toURI())).forEach(System.out::println);

Answer 3

Files.lines(Path) expects a Path argument and returns a Stream<String>. Stream#forEach(Consumer) expects a Consumer argument. So invoke the method, passing it a Consumer. That object will have to be implemented to do what you want for each line.

This is Java 8, so you can use lambda expressions or method references to provide a Consumer argument.

Answer 4

Avoid returning a list with:

List<String> lines = Files.readAllLines(path); //WARN

Be aware that the entire file is read when Files::readAllLines is called, with the resulting String array storing all of the contents of the file in memory at once. Therefore, if the file is significantly large, you may encounter an OutOfMemoryError trying to load all of it into memory.

Use stream instead: Use Files.lines(Path) method that returns a Stream<String> object and does not suffer from this same issue. The contents of the file are read and processed lazily, which means that only a small portion of the file is stored in memory at any given time.

Files.lines(path).forEach(System.out::println);

Answer 5

I have created a sample , you can use the Stream to filter/

public class ReadFileLines {
    public static void main(String[] args) throws IOException {
        Stream<String> lines = Files.lines(Paths.get("C:/SelfStudy/Input.txt"));
//      System.out.println(lines.filter(str -> str.contains("SELECT")).count());

//Stream gets closed once you have run the count method.
        System.out.println(lines.parallel().filter(str -> str.contains("Delete")).count());
    }
}

Sample input.txt.

SELECT Every thing
Delete Every thing
Delete Every thing
Delete Every thing
Delete Every thing
Delete Every thing
Delete Every thing