Java 按行读取文件

1. 使用 Scanner 按行读取文件

import java.io.*;
import java.util.Scanner;

class ReadFileWithScanner {
    public static void main(String[] args) throws FileNotFoundException {
        InputStream stream = new FileInputStream("src/main/resources/test-data.txt");
        //InputStream stream = ReadFileWithScanner.class.getClassLoader().getResourceAsStream("test-data.txt");
        Scanner scanner = new Scanner(stream);

        while (scanner.hasNextLine()) {
            System.out.println(scanner.nextLine());
        }
    }
}

2. 使用 BufferedReader 按行读取文件

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Objects;

class ReadFileWithBufferedReader {
    public static void main(String[] args) throws IOException {
        File file = new File("src/main/resources/test-data.txt");
        //URL fileUrl = ReadFileWithBufferedReader.class.getClassLoader().getResource("test-data.txt");
        //File file = new File(fileUrl.getFile());
        FileReader fileReader = new FileReader(file);
        BufferedReader bufferedReader = new BufferedReader(fileReader);
        String line;

        while (true) {
            line = bufferedReader.readLine();
            if (Objects.isNull(line)) {
                break;
            }

            System.out.println(line);
        }
    }
}

3. 使用 RandomAccessFile 按行读取文件

虽然是 Random，实际是顺序按行读取的。文件读取完毕后，可以通过 randomAccessFile.seek(0); 重置指针，再次从头读取文件。

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Objects;

class ReadFileWithRandomAccessFile {
    public static void main(String[] args) throws IOException, InterruptedException {
        File file = new File("src/main/resources/test-data.txt");
        //File file = new File(ReadFileWithRandomAccessFile.class.getClassLoader().getResource("test-data.txt").getFile());
        RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r");
        String line;

        while (true) {
            line = randomAccessFile.readLine();
            if (Objects.isNull(line)) {
                break;
            }

            System.out.println(line);
        }
    }
}

3. 使用 readAllLines 按行读取文件

注意，这个方法会把所有内容读取到内存当中，适合文件小的情况。

import java.io.IOException;
import java.net.URISyntaxException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;

class ReadFileWithReadAllLines {
    public static void main(String[] args) throws IOException, URISyntaxException, InterruptedException {
        Path path = Paths.get("src/main/resources/test-data.txt");
        //Path path = Paths.get(ReadFileWithReadAllLines.class.getClassLoader().getResource("test-data.txt").toURI());
        List<String> lines = Files.readAllLines(path);

        for (String line: lines) {
            System.out.println(line);
        }
    }
}