Java8流逐行讀取文件
在Java8中，可以使用Files.lines讀取文件的流。
c://lines.txt – 用於測試的簡單文本文件
line1 line2 line3 line4 line5
1. Java 8 讀取文件+流
TestReadFile.java
package com.yiibai.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();
}
}
}
輸出結果
line1 line2 line3 line4 line5
2. Java 8 讀取文件+流+額外
這個例子說明了如何使用數據流過濾內容，其全部內容轉換為大寫並返回一個列表。
TestReadFile2.java
package com.yiibai.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);
}
}
輸出結果
LINE1 LINE2 LINE4 LINE5
3. BufferedReader + Stream
一種新的方法lines() ，已經在JDK1.8已經添加，它讓 BufferedReader 返回流的內容。
TestReadFile3.java
package com.yiibai.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);
}
}
輸出結果
line1 line2 line3 line4 line5
4. BufferedReader和Scanner
上麵我們已經足夠了解Java8和流，現在重溫經典BufferedReader（JDK1.1）和Scanner （JDK1.5）的例子來逐行讀取文件中的行。
4.1 BufferedReader + 嘗試使用資源的例子。
TestReadFile4.java
package com.yiibai.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+使用資源的例子。
TestReadFile5.java
package com.yiibai.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();
}
}
}
參考
