生成10位16进制的数
public class ReadDeviceNo {// 获取一个String值public static String getString(Context context) {//读器SD卡文件  获取设备序列号 (如果有,读取这个序列号,没有就随机产生一个10位16进制的数)File file = new File(getFilePath(context));String num = "";if (file.exists()) {num = ReadTxt(file);}//判断这个数字 是否存在  并且长度是否等于10if (TextUtils.isEmpty(num) && num.length() != 10) {//随机生成1个10位进制的随机数num = getRandomValue(10);write(file, num);}return num;}//获取获取随机数private static String getFilePath(Context context) {String directoryPath = "";//判断SD卡是否可用if (MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {directoryPath = "mnt/sdcard";} else {//没内存卡就存机身内存directoryPath = context.getCacheDir().getAbsolutePath();}String filePath = directoryPath + File.separator + "cl.txt";File file = new File(directoryPath);if (!file.exists()) {//判断文件目录是否存在file.mkdirs();}return filePath;}//读取txt文件private static String ReadTxt(File file) {StringBuilder result = new StringBuilder();try {BufferedReader br = new BufferedReader(new FileReader(file));//构造一个BufferedReader类来读取文件String s = null;while ((s = br.readLine()) != null) {//使用readLine方法，一次读一行result.append(s);}br.close();} catch (Exception e) {e.printStackTrace();}return result.toString();}/*产生numSize位16进制的数*/public static String getRandomValue(int numSize) {String str = "";for (int i = 0; i < numSize; i++) {char temp = 0;int key = (int) (Math.random() * 2);switch (key) {case 0:temp = (char) (Math.random() * 10 + 48);//产生随机数字break;case 1:temp = (char) (Math.random() * 6 + 'a');//产生a-fbreak;default:break;}str = str + temp;}return str;}private static void write(File file, String content) {try {if (!file.exists()) {file.createNewFile();}StringBuilder sb = new StringBuilder();sb.append(content);RandomAccessFile raf = new RandomAccessFile(file, "rwd");raf.seek(file.length());raf.write(sb.toString().getBytes());raf.close();} catch (Exception e) {e.printStackTrace();}}
}