Java How to read a file into a list?
By:Roy.LiuLast updated:2019-08-11
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
d:\\server.log
1.2 Read file into a List
JavaExample.java
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
References
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