Java – How to read a file into a list?

By mkyong | Updated: December 20, 2018

Viewed: 16,677 (+96 pv/w)

Tags: java read file stream

In Java, there are few ways to read a file line by line into a List

1. Java 8 stream

	List<String> result;
	try (Stream<String> lines = Files.lines(Paths.get(fileName))) {
		result = lines.collect(Collectors.toList());
	}

2. Java 7

	Files.readAllLines(new File(fileName).toPath(), Charset.defaultCharset());

3. Classic BufferedReader example.

	List<String> result = new ArrayList<>();
	BufferedReader br = null;

	try {

		br = new BufferedReader(new FileReader(fileName));

		String line;
		while ((line = br.readLine()) != null) {
			result.add(line);
		}

	} catch (IOException e) {
		e.printStackTrace();
	} finally {
		if (br != null) {
			br.close();
		}
	}

1. File -> List

1.1 A dummy file

a
b
c
d
1
2
3

1.2 Read file into a List

package com.mkyong.example;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class JavaExample {

    public static void main(String[] args) {

        String filename = "d:\\server.log";

        try {
            List list = readByJavaClassic(filename);
            list.forEach(System.out::println);
        } catch (IOException e) {
            e.printStackTrace();
        }


    }

    private static List readByJava8(String fileName) throws IOException {
        List<String> result;
        try (Stream<String> lines = Files.lines(Paths.get(fileName))) {
            result = lines.collect(Collectors.toList());
        }
        return result;

    }

    private static List readByJava7(String fileName) throws IOException {
        return Files.readAllLines(new File(fileName).toPath(), Charset.defaultCharset());
    }

    private static List readByJavaClassic(String fileName) throws IOException {

        List<String> result = new ArrayList<>();
        BufferedReader br = null;

        try {

            br = new BufferedReader(new FileReader(fileName));

            String line;
            while ((line = br.readLine()) != null) {
                result.add(line);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (br != null) {
                br.close();
            }
        }

        return result;
    }

}

Output

a
b
c
d
1
2
3

References

1. Java 8 Stream – Read a file line by line