java IO流

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reader读取

    public static void main(String[] args) throws IOException{
        try (BufferedReader reader = new BufferedReader(new FileReader("D:\a.txt"));) {
            reader.lines().forEach(System.out::println);
        }
    }

在try（）的括号中写reader的定义语句，就不用在finally中关闭流，流会在try大括号{}内逻辑执行完成后自行关闭

writer写入

    public static void main(String[] args) throws IOException{
        try (BufferedReader reader = new BufferedReader(new FileReader("D:\a.txt"));
             FileWriter writer = new FileWriter("D:\b.txt")) {
            //换行符
            String property = System.getProperty("line.separator");
            reader.lines().forEach(str -> {
                try {
                    writer.write(str);
                    writer.write(property);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            });
        }
    }

写入时，每次写一行数据，最后添加换行

文件复制

    public static void main(String[] args) throws IOException {
        try (InputStream inputStream = new FileInputStream("D:\a.png");
             OutputStream outputStream = new FileOutputStream("D:\b.png")) {
            byte[] b = new byte[1024];
            int i = 0;
            while ((i = inputStream.read(b)) > 0) {
                outputStream.write(b, 0, i);
            }
        }
    }