A:http://download.pudn.com/downloads15/sourcecode/app/354278Cams.rar（随机数字6个）
B:http://www.pudn.com/downloads15/sourcecode/app/detail58144.html

规律
1截取B的url地址/downloads15/sourcecode/app
2截取B页面里面文件的名字
3判断下载资源的扩展名

download.pudn.com/1/2.3

download.pudn.com
download2.pudn.com
download3.pudn.com
download4.pudn.com
（需要四次的测试）

http://www.pudn.com/downloads204/sourcecode/math/detail962376.html
http://download2.pudn.com/downloads204/sourcecode/math/40128283opinionfinderv1.5.rar（随机数字8个）

http://www.pudn.com/downloads159/sourcecode/embed/detail711587.html
http://download.pudn.com/downloads159/sourcecode/embed/2549709344jianpan.rar（随机数字10个）

http://www.pudn.com/downloads261/sourcecode/windows/dialog/detail1201359.html
http://download3.pudn.com/downloads261/sourcecode/windows/dialog/977025389WeatherShow.rar（随机数字9个）

http://www.pudn.com/downloads293/sourcecode/windows/opengl/detail1314028.html
http://download3.pudn.com/downloads293/sourcecode/windows/opengl/891932011.rar（随机数字7个）

总结最后文件名是随机个数的随机数字，猜想有最短和最长限制。