Interview Questions and Answers

Google Gson is a Java library that can be used to convert Java Objects into respective JSON format. In another way, it can used to convert the JSON into equivalent java objects. There are some other java libraries also capable of doing this conversion, but Gson stands among very few which do not require any pre-annotated java classes OR sourcecode of java classes in any way.

Gson also support the old java classes which had not support of generics in them for type information. It just work with these legacy classes smoothly.

Gson object can be created in two ways. First way gives you a quick Gson object ready for faster coding, while second way uses GsonBuilder to build a more sophisticated Gson object.

Gson gson = new Gson();

To convert the java objects to JSON format, use toJson() method.

Employee employee = new Employee();

employee.setId(1);

employee.setFirstName("Arindam");

employee.setLastName("Ghosh");

employee.setRoles(Arrays.asList("FINANCE", "MANAGER"));

Gson gson = new Gson();

System.out.println(gson.toJson(employee));

To convert the JSON to java object, use fromJson() method.

Gson gson = new Gson();

System.out.println(

    gson.fromJson("{'id':1,'firstName':'Arindam','lastName':'Ghosh','roles':['FINANCE','MANAGER']}", 

    Employee.class));

     

Employee [id=1, firstName=Arindam, lastName=Ghosh, roles=[FINANCE, MANAGER]]