Java 8 Stream – Read a file line by line

In Java 8, you can use Files.lines to read file as Stream.

c://lines.txt – A simple text file for testing

line1

line2

line3

line4

line5

1. Java 8 Read File + Stream

TestReadFile.java

package com.mkyong.java8;

import java.io.IOException;

import java.nio.file.Files;

import java.nio.file.Paths;

import java.util.stream.Stream;

public class TestReadFile {

public static void main(String args[]) {

String fileName = "c://lines.txt";

//read file into stream, try-with-resources

try (Stream<String> stream = Files.lines(Paths.get(fileName))) {

stream.forEach(System.out::println);

} catch (IOException e) {

e.printStackTrace();

}

}

}

Output

line1

line2

line3

line4

line5

2. Java 8 Read File + Stream + Extra

This example shows you how to use Stream to filter content, convert the entire content to upper case and return it as a List.

TestReadFile2.java

package com.mkyong.java8;

import java.io.IOException;

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 TestReadFile2 {

public static void main(String args[]) {

String fileName = "c://lines.txt";

List<String> list = new ArrayList<>();

try (Stream<String> stream = Files.lines(Paths.get(fileName))) {

//1. filter line 3

//2. convert all content to upper case

//3. convert it into a List

list = stream

.filter(line -> !line.startsWith("line3"))

.map(String::toUpperCase)

.collect(Collectors.toList());

} catch (IOException e) {

e.printStackTrace();

}

list.forEach(System.out::println);

}

}

Output

LINE1

LINE2

LINE4

LINE5

3. BufferedReader + Stream

A new method lines() has been added since 1.8, it lets BufferedReader returns content as Stream.

TestReadFile3.java

package com.mkyong.java8;

import java.io.BufferedReader;

import java.io.IOException;

import java.nio.file.Files;

import java.nio.file.Paths;

import java.util.ArrayList;

import java.util.List;

import java.util.stream.Collectors;

public class TestReadFile3{

public static void main(String args[]) {

String fileName = "c://lines.txt";

List<String> list = new ArrayList<>();

try (BufferedReader br = Files.newBufferedReader(Paths.get(fileName))) {

//br returns as stream and convert it into a List

list = br.lines().collect(Collectors.toList());

} catch (IOException e) {

e.printStackTrace();

}

list.forEach(System.out::println);

}

}

Output

line1

line2

line3

line4

line5

4. Classic BufferedReader And Scanner

Enough of Java 8 and Stream, let revisit the classic BufferedReader (JDK1.1) and Scanner (JDK1.5) examples to read a file line by line, it is working still, just developers are moving toward Stream.

4.1 BufferedReader + try-with-resources example.

TestReadFile4.java

package com.mkyong.core;

import java.io.BufferedReader;

import java.io.FileReader;

import java.io.IOException;

public class TestReadFile4{

public static void main(String args[]) {

String fileName = "c://lines.txt";

try (BufferedReader br = new BufferedReader(new FileReader(fileName))) {

String line;

while ((line = br.readLine()) != null) {

System.out.println(line);

}

} catch (IOException e) {

e.printStackTrace();

}

}

}

4.2 Scanner + try-with-resources example.

TestReadFile5.java

package com.mkyong.core;

import java.io.File;

import java.io.IOException;

import java.util.Scanner;

public class TestReadFile5 {

public static void main(String args[]) {

String fileName = "c://lines.txt";

try (Scanner scanner = new Scanner(new File(fileName))) {

while (scanner.hasNext()){

System.out.println(scanner.nextLine());

}

} catch (IOException e) {

e.printStackTrace();

}

}

}

from:http://www.mkyong.com/java8/java-8-stream-read-a-file-line-by-line/

In Java 8, you can use Files.lines to read file as Stream.

c://lines.txt – A simple text file for testing

line1
line2
line3
line4
line5

Copy

1. Java 8 Read File + Stream

TestReadFile.java

package com.mkyong.java8;

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

public class TestReadFile {

	public static void main(String args[]) {

		String fileName = "c://lines.txt";

		//read file into stream, try-with-resources
		try (Stream<String> stream = Files.lines(Paths.get(fileName))) {

			stream.forEach(System.out::println);

		} catch (IOException e) {
			e.printStackTrace();
		}

	}

}

Copy

Output

line1
line2
line3
line4
line5