字节流

• 初始化变量

  private static final String FILENAME = "E:" + File.separator + "hello.txt";
  

向文件中写入字符串

private static void testWriteFile() {
    File file = new File(FILENAME);
    try {
        //默认覆盖原内容，不向文件中追加新内容
        OutputStream os = new FileOutputStream(file);
        String txt = "你好，世界！";
        byte[] bytes = txt.getBytes();
        os.write(bytes);
        os.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private static void testWriteFileWithByte() {
    File file = new File(FILENAME);
    try {
        //向文件中追加内容
        OutputStream os = new FileOutputStream(file, true);
        String txt = "你好，世界！";
        byte[] bytes = txt.getBytes();
        for (byte b : bytes) {
            os.write(b);
        }
        os.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

读取文件内容

private static void testReadFile() {
    File file = new File(FILENAME);
    try {
        InputStream is = new FileInputStream(file);
        byte[] bytes = new byte[1024];
        int length = is.read(bytes);
        is.close();
        System.out.println("读取长度：" + length);
        System.out.println("读取内容：" + new String(bytes));
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private static void testReadFileUnknownSize() {
    File file = new File(FILENAME);
    try {
        InputStream is = new FileInputStream(file);
        //注意byte数组的初始大小，如果读取的数据大小超出时会报错
        byte[] bytes = new byte[1024];
        int count = 0;
        int temp;
        //只有当读到文件末尾的时候会返回-1
        while((temp = is.read()) != -1) {
            bytes[count++] = (byte) temp;
        }
        is.close();
        System.out.println(new String(bytes));
    } catch (IOException e) {
        e.printStackTrace();
    }
}