Java优学网字符流教程：轻松掌握文件读写与编码处理技巧

// 显式指定UTF-8编码 Reader reader = new InputStreamReader(new FileInputStream("file.txt"), "UTF-8");

public class FileCharCopy {

public static void main(String[] args) {
    try (Reader reader = new FileReader("source.txt");
         Writer writer = new FileWriter("target.txt")) {
        
        char[] buffer = new char[1024];
        int charsRead;
        
        while ((charsRead = reader.read(buffer)) != -1) {
            writer.write(buffer, 0, charsRead);
        }
        
    } catch (IOException e) {
        e.printStackTrace();
    }
}

}

try (FileChannel channel = FileChannel.open(Paths.get("hugefile.txt"), StandardOpenOption.READ)) {

MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
CharsetDecoder decoder = StandardCharsets.UTF_8.newDecoder();
CharBuffer charBuffer = decoder.decode(buffer);

// 处理字符数据
while (charBuffer.hasRemaining()) {
    processChar(charBuffer.get());
}

}