java - Unable to parse Json array using Gson

Question

I have this json array:

 [
{
"id":18,
"city":"??????",
"street":"??????? 1",
"zipcode":121209,
"state":"IL",
"lat":32.158138,
"lng":34.807838
},
{
"id":19,
"city":"??????",
"street":"??? ??? 1",
"zipcode":76812,
"state":"IL",
"lat":32.161041,
"lng":34.810410
}
]

And i have this class to hold the data:

public class MapData {
    private int id;
    private String city;
    private String street;
    private String state;
    private int zipcode;
    private double lat;
    private double lng;

    public MapData(int id, String city, String street, String state,
            int zipcode, double lat, double lng) {          
        this.id = id;
        this.city = city;
        this.street = street;
        this.state = state;
        this.zipcode = zipcode;
        this.lat = lat;
        this.lng = lng;
    }

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    public String getStreet() {
        return street;
    }
    public void setStreet(String street) {
        this.street = street;
    }
    public String getState() {
        return state;
    }
    public void setState(String state) {
        this.state = state;
    }
    public int getZipcode() {
        return zipcode;
    }
    public void setZipcode(int zipcode) {
        this.zipcode = zipcode;
    }
    public double getLat() {
        return lat;
    }
    public void setLat(double lat) {
        this.lat = lat;
    }
    public double getLng() {
        return lng;
    }
    public void setLng(double lng) {
        this.lng = lng;
    }

}   

I'm trying to convert the json into a List of MapData objects:

Type type = new TypeToken<List<MapData>>(){}.getType();
return gson.fromJson(jsonString, type);

But i get this error:

java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to com.deliveries.models.MapData

What am i doing wrong?

Answer 1

I suspect that the method calling fromJson is returning the wrong type. It should return a List<MapData> instead of MapData.

Something like:

public static List<MapData> getData(){
    Gson gson = new Gson();
    String jsonString = "[{"id":18,"city":"test","street":"test 1","zipcode":121209,"state":"IL","lat":32.158138,"lng":34.807838},{"id":19,"city":"test","street":"1","zipcode":76812,"state":"IL","lat":32.161041,"lng":34.810410}]";
    Type type = new TypeToken<List<MapData>>(){}.getType();
    return gson.fromJson(jsonString, type);     
}

I have a fully working example of your issue in this Gist