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();
}
}
}
References
- Java 8 File.lines()Java 8 StreamJava BufferedReader
link: https://www.mkyong.com/java8/java-8-stream-read-a-file-line-by-line/
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