Difference between HTTP PUT and POST

Difference between PUT and POST

The key difference between PUT and POST is that PUT is idempotent while POST is not. No matter how many times you send a PUT request, the results will be same. POST is not an idempotent method. Making a POST multiple times may result in multiple resources getting created on the server.

Another difference is that, with PUT, you must always specify the complete URI of the resource. This implies that the client should be able to construct the URI of a resource even if it does not yet exist on the server. This is possible when it is the client's job to choose a unique name or ID for the resource, just like creating a user on the server requires the client to choose a user ID. If a client is not able to guess the complete URI of the resource, then you have no option but to use POST.

Request	Operation
PUT http://MyService/Persons/	Won't work. PUT requires a complete URI
PUT http://MyService/Persons/1	Insert a new person with PersonID=1 if it does not already exist, or else update the existing resource
POST http://MyService/Persons/	Insert a new person every time this request is made and generate a new PersonID.
POST http://MyService/Persons/1	Update the existing person where PersonID=1

It is clear from the above table that a PUT request will not modify or create more than one resource no matter how many times it is fired (if the URI is same). There is no difference between PUT and POST if the resource already exists, both update the existing resource. The third request (POST http://MyService/Persons/) will create a resource each time it is fired.