Java – How to read a file into a list?
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
a
b
c
d
1
2
3
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
a
b
c
d
1
2
3
References
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