java8-read-file-读文件
目录
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
line1
line2
line3
line4
line5Java 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
line5Java 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
LINE5BufferedReader + 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
line5Classic 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();
}
}
}