java8 read file 读文件

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

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

line1line2line3line4line5

 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-resourcestry (Stream<String> stream = Files.lines(Paths.get(fileName))) {stream.forEach(System.out::println);} catch (IOException e) {e.printStackTrace();}}}

Output

line1line2line3line4line5

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 aList.

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 Listlist = stream.filter(line -> !line.startsWith("line3")).map(String::toUpperCase).collect(Collectors.toList());} catch (IOException e) {e.printStackTrace();}list.forEach(System.out::println);}}

Output

LINE1LINE2LINE4LINE5

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 Listlist = br.lines().collect(Collectors.toList());} catch (IOException e) {e.printStackTrace();}list.forEach(System.out::println);}}

Output

line1line2line3line4line5

 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();}}}