读取文件

 List<String> lines = Files.readAllLines(Paths.get("/Users/cong/3.txt"), StandardCharsets
                .UTF_8);

写入文件

 PrintStream out = new PrintStream(newFileOutputStream("/Users/cong/Desktop/pass/passwd.txt"));
 out.println(stringBuilder.toString());

读取大文件

 try {
        FileChannel fileChannel = FileChannel.open(Paths.get("/Users/cong/Downloads/crackstation-human-only.txt"), StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE);

        MappedByteBuffer mbb = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, 900);
        Charset charset = Charset.forName("utf-8");
        CharsetDecoder decoder = charset.newDecoder();
        CharBuffer charBuffer = decoder.decode(mbb);
        Scanner sc = new Scanner(charBuffer).useDelimiter(System.getProperty("line.separator"));
        while (sc.hasNext()) {
            String next = sc.next();
            System.out.println(next);


        }

    } catch (Exception e) {
        e.printStackTrace();
    }</xmp></code></pre>