How to fill values of variables in json file dynamically in java

I have a json file which looks like

{
  name = VARIABLE1
  age = VARIABLE2
  address
  {
    street = VARIABLE3
    line = VARIABLE4
  }
}

So now i want to read the file in java code and generate the values of VARIABLES and generate the json and post it to a server. Which means i am testing the server with same kind of data but with different values.

How can i do this