从File中读取文件十六进制内容，途中进行补位

HexUtil.java

 public static final String readHexContent(String filePath) {
        FileInputStream in = null;
        try {
            in = new FileInputStream(filePath);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }


        int b = 0;
        int i = 1;
        StringBuilder builder = new StringBuilder();
        while (in != null)//b=in.read()这就是程序核心
        {
            try {
                if ((b = in.read()) == -1) {
                    break;
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            String item = Integer.toHexString(b);
            if (item.length() == 1) {
                builder.append("0");
            }
            builder.append(item);

        }

        try {
            in.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return builder.toString().trim();
    }