总结：

NSURL *url = [NSURL URLWithString:@"http://www.baidu.com:8848/search/path?username=1&password=2"];
//协议  scheme：http
NSLog(@"scheme：%@",[url scheme]);
//域名  host：www.baidu.com
NSLog(@"host：%@",[url host]);
//完整URL字符串  absoluteString：http://www.baidu.com/search/path?username=1&password=2
NSLog(@"absoluteString：%@",[url absoluteString]);
//相对路径  relativePath：/search/path
NSLog(@"relativePath：%@",[url relativePath]);
//端口号  port：8848
NSLog(@"port：%@",[url port]);
//search  pathComponent：( "/", search,  path)
NSLog(@"pathComponent：%@",[url pathComponents]);
//参数  Query：username=1&password=2
NSLog(@"Query：%@",[url query]);