Trouble mapping JSON data to Java object

Question

I'm having a little trouble working out an appropriate java object structure for the following JSON data:

"pages": {
            "181382": {
                "pageid": 181382,
                "ns": 0,
                "title": "Anonymity"
            },
            "7181837": {
                "pageid": 7181837,
                "ns": 0,
                "title": "Anonymous"
            }
        }

The identifiers "181382" and "7181837" change depending on the data returned so these cannot be used as a member on an object. I tried to approach it using a Map<String, Object> approach but got a little stuck.

Edit: This is what I've tried

public class PageData {

    int pageid;
    String ns;
    String title;

    public int getPageid() {
        return pageid;
    }

    public String getNs() {
        return ns;
    }

    public String getTitle() {
        return title;
    }

}



Map<String, PageData> pages = results.getPages().getData();

        for (PageData data : pages.values()) {
            System.out.println(data.getTitle());
        }

Where did you get stuck? Show us how you tried to map it. You can map the object named 7181837 to a POJO and use a Map<String, YourPojo>. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Jan 9, 2014 at 21:14
Well it just wasn't mapping correctly so it threw null pointers when I tried to access any of the data — Ben Dale
– Ben Dale, Commented Jan 9, 2014 at 21:15
So post the actual JSON, actual DTOs/POJOs, and actual usage of such. Chance are a level if "off". — user2864740
– user2864740, Commented Jan 9, 2014 at 21:15
Seems to me it's a Map containing two more Maps. If you wish you can replace the inner Maps with Page objects, but there's no compelling reason to do so. — Hot Licks
– Hot Licks, Commented Jan 9, 2014 at 21:18
class PageCollection { public Map<String, PageData> pages; } might be useful .. chances are you're deserializing off by a level as the JSON Object related to the Map is the value of the pages property. (Also, you should still show the usage of the GSON). — user2864740
– user2864740, Commented Jan 9, 2014 at 21:18

Maxim Shoustin · Accepted Answer · 2014-01-09 21:24:23Z

Just create some wrapper for your Object. Here is working example:

Wrapper

public class Wrapper {
    Map<String, PageData> pages = null;

    public Map<String, PageData> getPages() {
        return pages;
    }   
}

Launcher

public class Launcher {
    public static void main(String[] args) {
        String str = "{\"pages\": {\r\n" + 
                "            \"181382\": {\r\n" + 
                "                \"pageid\": 181382,\r\n" + 
                "                \"ns\": 0,\r\n" + 
                "                \"title\": \"Anonymity\"\r\n" + 
                "            },\r\n" + 
                "            \"7181837\": {\r\n" + 
                "                \"pageid\": 7181837,\r\n" + 
                "                \"ns\": 0,\r\n" + 
                "                \"title\": \"Anonymous\"\r\n" + 
                "            }\r\n" + 
                "        }" +
                "}";


        Gson gson = new Gson();

        Wrapper results = gson.fromJson(str, Wrapper.class);

        Map<String, PageData> pages = results.getPages();

        for (PageData data : pages.values()) {
            System.out.println(data.getTitle());
        }
    }
}

PageData

public class PageData{/* the same */}

Output:

Anonymity
Anonymous

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