JSON response with arraylist

Question

I am new to JSON and jQuery and I want to get JSON data using AJAX. I want to show data using a submit button I try like this:

PrintWriter out = response.getWriter();
List<Countries> country = new ArrayList<Countries>();
country = FetchData.getAllCountries();
JSONObject js = new JSONObject();
JSONArray jsonArray = new JSONArray(country);

// set the response content-type
response.setContentType("application/json");

// writing the json-array to the output stream
out.print(jsonArray);
out.flush();

I get a compile time error: The constructor JSONArray(List<Countries>) is undefined. below way i try it working but i want to implemt using jason array

           PrintWriter out = response.getWriter();
    ArrayList<Countries> country = new ArrayList<Countries>();
    country = FetchData.getAllCountries();
    String json = new Gson().toJson(country);
    response.setContentType("application/json");
    response.setCharacterEncoding("UTF-8");
    out.write(json);

working below way

ArrayList<Countries> country=new ArrayList<Countries>();
country=FetchData.getAllCountries();
Gson gson = new Gson();
JsonElement element = gson.toJsonTree(country, new TypeToken<List<Countries>>() {}.getType());

JsonArray jsonArray = element.getAsJsonArray();
response.setContentType("application/json");
response.getWriter().print(jsonArray);

The error means JSONArray does not accept a List / or only a List in it's constructor. — Daniel Cheng
– Daniel Cheng, Commented May 6, 2014 at 8:41
arraylist response using jsaon array is possible or any other solution — user3607292
– user3607292, Commented May 6, 2014 at 8:45
Look what I found! code.google.com/p/json-simple/wiki/EncodingExamples .... its the Wiki for that json library, it contains encoding examples. Check them out. — ug_
– ug_, Commented May 6, 2014 at 8:51

RTF · Accepted Answer · 2014-05-06 16:15:45Z

1

Is that the json-simple library you're using? If it is:

PrintWriter out = response.getWriter();
List<Countries> country = new ArrayList<Countries>();
country = FetchData.getAllCountries();
JSONObject js = new JSONObject();
js.put("countries", country); // make sure the Country class overrides toString()

// set the response content-type
response.setContentType("application/json");

// writing the json-array to the output stream
out.print(js.toJSONString());
out.flush();

You seem to be trying to insert an anonymous array into your json string. You can't do that, it's not valid JSON. For example, your JSON cannot look like:

{
    ["1st Country", "2nd Country", "3rd Country"]
}

...there needs to be at least one key/value pair in JSON e.g.

{
    "countries": ["1st Country", "2nd Country", "3rd Country"]
}

...so "countries" is the key and the array is the value. If you use the example code I gave above, then your server should return a JSON string to the browser that looks like the valid JSON example above. So, if your client javascript is calling the server using an AJAX call like this (using jQuery):

$.ajax({
    type:     'GET',
    url:      '/your-server-path',
    dataType: 'json',
    success:  function(response, status, request) {
        // jQuery automatically converts the JSON object to a Javascript object 
        for (int i=0; i<response.countries.length; i++) {
            console.log("Country " + i + " is " + response.countries[i]);
        }
    }, 
    error: function(request, status, error) {
        console.log("Something went wrong...");
    }
});

Also, as I mentioned in the first code snippet, you must override the toString() method of your Country class, so that each Country instance can be converted to a string and added to the JSON array e.g.

@Override
public String toString() {
    // return some combination of variables in your Country class
    // or however you want a Country to be represented
}

edited May 6, 2014 at 16:15

answered May 6, 2014 at 8:53

RTF

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2 Comments

user3607292 Over a year ago

client side which way to set resopnse because above way implmenting got error errror (object object)

user3607292 Over a year ago

ArrayList<Countries> country=new ArrayList<Countries>(); country=FetchData.getAllCountries(); Gson gson = new Gson(); JsonElement element = gson.toJsonTree(country, new TypeToken<List<Countries>>() {}.getType()); JsonArray jsonArray = element.getAsJsonArray(); response.setContentType("application/json"); response.getWriter().print(jsonArray);

ug_ · Accepted Answer · 2014-05-06 08:52:29Z

From the Wiki for json-simple https://code.google.com/p/json-simple/wiki/EncodingExamples#Example_2-4_-_Encode_a_JSON_array_-_Using_List_and_streaming

LinkedList list = new LinkedList();
list.add("foo");
list.add(new Integer(100));
list.add(new Double(1000.21));
list.add(new Boolean(true));
list.add(null);
StringWriter out = new StringWriter();
JSONValue.writeJSONString(list, out);
String jsonText = out.toString();
System.out.print(jsonText);

So yours would be

PrintWriter out = response.getWriter();
List<Countries> country = new ArrayList<Countries>();
country = FetchData.getAllCountries();
JSONObject js = new JSONObject();
JSONArray jsonArray = new JSONArray(country);

StringWriter out = new StringWriter();
JSONValue.writeJSONString(country, out);

// set the response content-type
response.setContentType("application/json");

// writing the json-array to the output stream
out.print(out.toString());
out.flush();

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