Getting null values while deserialize json string to textview gson

Question

I am newbie, I have created webservice in java for get all Restaurant category from MySQL database and accessing in android studio ,

my json response is as following,

[
{
    "restro": {
        "categoryid": 1,
        "categoryname": "Restaurant (Vegetarian)"
    }
},
{
    "restro": {
        "categoryid": 2,
        "categoryname": "Restaurant (Non-Vegetarian)"
    }
}
]  

deserialization code gson library

Gson gson=new Gson();
        Type RestroTypeListType=new TypeToken<Collection<Category>>(){}.getType();
        List<Category> categories=(List<Category>)gson.fromJson(jsonstring,RestroTypeListType);
        tv1.setText("");
        for(Category category : categories)
        {
              tv1.append(category.getCategoryName()+"\n");
        }

my entity class is

public class Category {

private int categoryID;
private String categoryName;

public Category() {

}

public int getCategoryID() {
    return categoryID;
}

public void setCategoryID(int categoryID) {
    this.categoryID = categoryID;
}

public String getCategoryName() {
    return categoryName;
}

public void setCategoryName(String categoryName) {
    this.categoryName = categoryName;
}

@Override
public String toString() {
    return "Category{" +
            ", categoryName='" + categoryName + '\'' +
            '}';
}

}

I am getting null in textview.

Answer 1

Your problem is that you are expecting a collection of categories but you are returning a collection of restro.

Can you provide more detail about the restro attribute in your json response.

But i guess that introducing a new Class that has an attribute named (restro) of type Category will solve your problem.

And change

Type RestroTypeListType=new TypeToken<Collection<Category>>(){}.getType();

For

Type RestroTypeListType=new TypeToken<Collection<Restro>>(){}.getType();

Answer 2

yeah, I got the answer

without add any external library ,

JSONArray jsonArray = new JSONArray(jsonstring);
        String OuterstringArray;
        tv1.setText("");
        for (int outer = 0; outer < jsonArray.length(); outer++) {
            OuterstringArray=jsonArray.getJSONObject(outer).getString("restro");
            JSONObject jsonObject=new JSONObject(OuterstringArray);

            arrayListRestro.add(jsonObject.getString("categoryname"));
        }
        ArrayAdapter arrayAdapter=new ArrayAdapter(this,android.R.layout.simple_list_item_1,arrayListRestro);
        listRestros.setAdapter(arrayAdapter);