json to java object with gson ( object nested with arraylist )

问题

I want to create a object Checklist with the following JSON. But I think the Arraylist categories isn't created. I do not have an exception the debug console enter into bucle when create the object : " Background partial concurrent mark sweep GC freed 165848(5MB) AllocSpace objects, 144(1852KB) LOS objects, 22% free, 55MB/71MB, paused 5.343ms total 67.660ms "

{"type_check":"CAB","description":"simple cabin","categories":[{"category_id":"3","description":"Confort"},{"category_id":"4","description":"Servicios"},{"category_id":"5","description":"Alimentación"},{"category_id":"6","description":"Personal"},{"category_id":"7","description":"Instalaciones"}]}

And the following classes:

Checklist.class

public class Checklist {

private String type_check;
private String description;
private ArrayList<Category> categories;}

Category.class

public class Category {


private int category_id;
private String description;

}

Creating the object:

 Gson gson = new GsonBuilder().create();
                            Checklist check = gson.fromJson(checklist.toString(), Checklist.class);

I must specify the arraylist when I parse the json?? Thanks and have a nice day.

回答1:

this is how the json would look like with following code

[
  {
"type_check": "CAB_0",
"description": "simple cabin",
"categories": [
  {
    "category_id": 0,
    "description": "Description_0"
  },
  {
    "category_id": 1,
    "description": "Description_1"
  },
  {
    "category_id": 2,
    "description": "Description_2"
  },
  {
    "category_id": 3,
    "description": "Description_3"
  },
  {
    "category_id": 4,
    "description": "Description_4"
  },
  {
    "category_id": 5,
    "description": "Description_5"
  },
  {
    "category_id": 6,
    "description": "Description_6"
  }
]

}, { "type_check": "CAB_1", "description": "simple cabin", "categories": [ { "category_id": 0, "description": "Description_0" }, { "category_id": 1, "description": "Description_1" }, { "category_id": 2, "description": "Description_2" }, { "category_id": 3, "description": "Description_3" }, { "category_id": 4, "description": "Description_4" }, { "category_id": 5, "description": "Description_5" }, { "category_id": 6, "description": "Description_6" } ] }, { "type_check": "CAB_2", "description": "simple cabin", "categories": [ { "category_id": 0, "description": "Description_0" }, { "category_id": 1, "description": "Description_1" }, { "category_id": 2, "description": "Description_2" }, { "category_id": 3, "description": "Description_3" }, { "category_id": 4, "description": "Description_4" }, { "category_id": 5, "description": "Description_5" }, { "category_id": 6, "description": "Description_6" } ] }, { "type_check": "CAB_3", "description": "simple cabin", "categories": [ { "category_id": 0, "description": "Description_0" }, { "category_id": 1, "description": "Description_1" }, { "category_id": 2, "description": "Description_2" }, { "category_id": 3, "description": "Description_3" }, { "category_id": 4, "description": "Description_4" }, { "category_id": 5, "description": "Description_5" }, { "category_id": 6, "description": "Description_6" } ] }, { "type_check": "CAB_4", "description": "simple cabin", "categories": [ { "category_id": 0, "description": "Description_0" }, { "category_id": 1, "description": "Description_1" }, { "category_id": 2, "description": "Description_2" }, { "category_id": 3, "description": "Description_3" }, { "category_id": 4, "description": "Description_4" }, { "category_id": 5, "description": "Description_5" }, { "category_id": 6, "description": "Description_6" } ] }, { "type_check": "CAB_5", "description": "simple cabin", "categories": [ { "category_id": 0, "description": "Description_0" }, { "category_id": 1, "description": "Description_1" }, { "category_id": 2, "description": "Description_2" }, { "category_id": 3, "description": "Description_3" }, { "category_id": 4, "description": "Description_4" }, { "category_id": 5, "description": "Description_5" }, { "category_id": 6, "description": "Description_6" } ] }, { "type_check": "CAB_6", "description": "simple cabin", "categories": [ { "category_id": 0, "description": "Description_0" }, { "category_id": 1, "description": "Description_1" }, { "category_id": 2, "description": "Description_2" }, { "category_id": 3, "description": "Description_3" }, { "category_id": 4, "description": "Description_4" }, { "category_id": 5, "description": "Description_5" }, { "category_id": 6, "description": "Description_6" } ] } ]

Checklist.Java code is here

public class Checklist {

private String type_check;
private String description;
private ArrayList<Category> categories;

public String getType_check() {
    return type_check;
}

public void setType_check(String type_check) {
    this.type_check = type_check;
}

public String getDescription() {
    return description;
}

public void setDescription(String description) {
    this.description = description;
}

public ArrayList<Category> getCategories() {
    return categories;
}

public void setCategories(ArrayList<Category> categories) {
    this.categories = categories;
}

}

Category.java code is here

public class Category {

private int category_id;
private String description;

public int getCategory_id() {
    return category_id;
}
public void setCategory_id(int category_id) {
    this.category_id = category_id;
}
public String getDescription() {
    return description;
}
public void setDescription(String description) {
    this.description = description;
}


}

TestCode.Java code is here

import java.util.ArrayList;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class TestCode {

public static void main(String[] args) {
    ArrayList<Checklist> list = new ArrayList<Checklist>();

    list = createList();

    String stringJson = (new Gson()).toJson(list);

    System.out.println("##### JSON from a object #######");

    System.out.println(stringJson);

    System.out.println("###### Convert JSON to object ######");

    ArrayList<Checklist> list2 = new ArrayList<Checklist>();

    list2 = (new Gson()).fromJson(stringJson,
            new TypeToken<ArrayList<Checklist>>() {
            }.getType());

    System.out.println("####### print out put ######");

    for (int i = 0; i < list2.size(); i++) {
        Checklist checklist = list2.get(i);
        System.out.println(checklist.getType_check() + "");
        System.out.println(checklist.getDescription() + "");

        ArrayList<Category> categorys = checklist.getCategories();

        for (int j = 0; j < categorys.size(); j++) {
            Category category = categorys.get(j);
            System.out.println(category.getCategory_id() + "");
            System.out.println(category.getDescription() + "");
        }

    }

}

private static ArrayList<Checklist> createList() {
    // TODO Auto-generated method stub
    ArrayList<Checklist> list = new ArrayList<Checklist>();

    for (int i = 0; i < 7; i++) {
        Checklist checklist = new Checklist();
        checklist.setType_check("CAB_" + i);
        checklist.setDescription("simple cabin");

        ArrayList<Category> categorys = new ArrayList<Category>();

        for (int j = 0; j < 7; j++) {
            Category category = new Category();
            category.setCategory_id(j);
            category.setDescription("Description_" + j);
            categorys.add(category);
        }
        checklist.setCategories(categorys);
        list.add(checklist);
    }

    return list;
}

}

来源：https://stackoverflow.com/questions/29251870/json-to-java-object-with-gson-object-nested-with-arraylist