Hangzhou to Shanghai

You can do it on the day of travel, but if so, you need to be there early like 90min in advance. Sometimes the waiting line can be very long.

Is that possible business class ticket gonna be sold out if i purchase on the same day of travel? If i do ticket purchase in advance through online, i still have to be at railway station 90 minutes earlier to collect the tickets? As i don't know whether ticket collection counter gonna be as long queue as ticket purchase counter.

Some of them may sold out, but since their many rails a day, you can wait for the next available one if you are not tight in time. As for the waiting line, in fact, most station do not have special ling for collection only.