Convert json array to a java list object [duplicate]

Question

I got an json array from server response:

[{"id":1, "name":"John", "age": 20},{"id":3, "name":"Tomas", "age": 29}, {"id":12, "name":"Kate", "age": 32}, ...]

I would like to use gson to convert the above json data to a Java List<Person> object. I tried the following way:

Firstly, I created a Person.java class:

public class Person{
  private long id;
  private String name;
  private int age;

  public long getId(){
     return id;
  }

  public String getName(){
     return name;
  }

  public int getAge(){
     return age;
  }
}

Then, in my service class, I did the following:

//'response' is the above json array 
List<Person> personList = gson.fromJson(response, List.class); 

for(int i=0; i<personList.size(); i++){
   Person p = personList.get(i); //java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to Person
}

I got Exception java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to Person . How to get rid of my problem? I just want to convert the json array to a List<Person> object. Any help?

Answer 1

You need to use a supertype token for the unmarshalling, so that Gson knows what the generic type in your list is. Try this:

TypeToken<List<Person>> token = new TypeToken<List<Person>>(){};
List<Person> personList = gson.fromJson(response, token.getType());

And iterate through the results as such:

for(Person person : personList) {
    // some code here
}