Is it possible to connect 3 LM317s in parallel to get upto 4A of current output ? I need 4A but I'm not able to figure out any other possibility. Is there any other possibility to achieve this ?
Yes, it is possible. Do not connect the outputs directly together but rather put a small resistor (0.5 Ohm or so) between each output and the summing node.
Check: http://www.ti.com/lit/ds/symlink/lm317.pdf 8.3.11 Adjustable 4-A Regulator Circuit on page 15/16.
You can also look at 9.3.13 which generates higher current with a single LM317, using instead NPN's to deliver the extra current.