How to convert list data into json in java

Question

I have a function which is returning Data as List in java class. Now as per my need, I have to convert it into Json Format.

Below is my function code snippet:

public static List<Product> getCartList() {
    List<Product> cartList = new Vector<Product>(cartMap.keySet().size());
    for(Product p : cartMap.keySet()) {
        cartList.add(p);
    }
    return cartList;
}

I tried To convert into json by using this code but it is giving type mismatch error as function is of type List...

public static List<Product> getCartList() {
    List<Product> cartList = new Vector<Product>(cartMap.keySet().size());
    for(Product p : cartMap.keySet()) {
        cartList.add(p);
    }

    Gson gson = new Gson();
     // convert your list to json
     String jsonCartList = gson.toJson(cartList);
     // print your generated json
     System.out.println("jsonCartList: " + jsonCartList);

     return jsonCartList;

        }

Please help me resolve this.

@vikas See if this helps you - kodejava.org/examples/588.html — Jeevan Patil
– Jeevan Patil, Commented Mar 11, 2013 at 6:57

anubhava · Accepted Answer · 2013-03-11 06:59:58Z

37

Using gson it is much simpler. Use following code snippet:

 // create a new Gson instance
 Gson gson = new Gson();
 // convert your list to json
 String jsonCartList = gson.toJson(cartList);
 // print your generated json
 System.out.println("jsonCartList: " + jsonCartList);

Converting back from JSON string to your Java object

 // Converts JSON string into a List of Product object
 Type type = new TypeToken<List<Product>>(){}.getType();
 List<Product> prodList = gson.fromJson(jsonCartList, type);

 // print your List<Product>
 System.out.println("prodList: " + prodList);

answered Mar 11, 2013 at 6:59

anubhava

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6 Comments

vikas Over a year ago

Sir i tried with follwoing code but Giving Type Mismatch error "public static List<Product> getCartList() { List<Product> cartList = new Vector<Product>(cartMap.keySet().size()); for(Product p : cartMap.keySet()) { cartList.add(p); } Gson gson = new Gson(); // convert your list to json String jsonCartList = gson.toJson(cartList); // print your generated json System.out.println("jsonCartList: " + jsonCartList); return jsonCartList; }"

vikas Over a year ago

Because function is in List and it is returning string

anubhava Over a year ago

Can you change List<Product> cartList = new Vector<Product>(cartMap.keySet().size()); to this: List<Product> cartList = new ArrayList<Product>(cartMap.keySet().size());

anubhava Over a year ago

Or better: List<Product> cartList = new ArrayList<Product>(cartMap.keySet()); then no need to run any for loop.

vikas Over a year ago

Sir it is giving type mismatch error as it is returning string and function is in List

|

PSR · Accepted Answer · 2013-03-11 10:56:28Z

20

public static List<Product> getCartList() {

    JSONObject responseDetailsJson = new JSONObject();
    JSONArray jsonArray = new JSONArray();

    List<Product> cartList = new Vector<Product>(cartMap.keySet().size());
    for(Product p : cartMap.keySet()) {
        cartList.add(p);
        JSONObject formDetailsJson = new JSONObject();
        formDetailsJson.put("id", "1");
        formDetailsJson.put("name", "name1");
       jsonArray.add(formDetailsJson);
    }
    responseDetailsJson.put("forms", jsonArray);//Here you can see the data in json format

    return cartList;

}

you can get the data in the following form

{
    "forms": [
        { "id": "1", "name": "name1" },
        { "id": "2", "name": "name2" } 
    ]
}

edited Mar 11, 2013 at 10:56

answered Mar 11, 2013 at 6:52

PSR

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6 Comments

vikas Over a year ago

thnx sir for ur response ..plz sir tell me what to add in this code: " formDetailsJson.put("...", "...");"

PSR Over a year ago

you need to add related jar files to class path which contain org.json.simple.JSONArray,org.json.simple.JSONObject classes.

vikas Over a year ago

Sir i need to know what to add as argument in this "formDetailsJson.put("...", "..."); formDetailsJson.put("...", "...");"

vikas Over a year ago

And those jar file i ahave added sir

PSR Over a year ago

you need to put name with which name you are going to access in the javascript

|

LocoGris · Accepted Answer · 2019-03-12 08:08:07Z

8

Try these simple steps:

ObjectMapper mapper = new ObjectMapper();
String newJsonData = mapper.writeValueAsString(cartList);
return newJsonData;
ObjectMapper() is com.fasterxml.jackson.databind.ObjectMapper.ObjectMapper();

edited Mar 12, 2019 at 8:08

LocoGris

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answered Mar 12, 2019 at 7:24

codelover

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Comments

Daniel Robertus · Accepted Answer · 2013-03-11 06:53:27Z

0

i wrote my own function to return list of object for populate combo box :

public static String getJSONList(java.util.List<Object> list,String kelas,String name, String label) {
        try {
            Object[] args={};
            Class cl = Class.forName(kelas);
            Method getName = cl.getMethod(name, null);
            Method getLabel = cl.getMethod(label, null);
            String json="[";
            for (int i = 0; i < list.size(); i++) {
            Object o = list.get(i);
            if(i>0){
                json+=",";
            }
            json+="{\"label\":\""+getLabel.invoke(o,args)+"\",\"name\":\""+getName.invoke(o,args)+"\"}";
            //System.out.println("Object = " + i+" -> "+o.getNumber());
            }
            json+="]";
            return json;
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(JSONHelper.class.getName()).log(Level.SEVERE, null, ex);
        } catch (Exception ex) {
            System.out.println("Error in get JSON List");
            ex.printStackTrace();
        }
        return "";
    }

and call it from anywhere like :

String toreturn=JSONHelper.getJSONList(list, "com.bean.Contact", "getContactID", "getNumber");

answered Mar 11, 2013 at 6:53

Daniel Robertus

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2 Comments

anstarovoyt Over a year ago

Usage += for string is very bad practice in loop

Daniel Robertus Over a year ago

yup, i just have a little bit data so its not effect that much.. if you work with lot of data you can use StringBuilder or StringBuffer.

ArifMustafa · Accepted Answer · 2018-04-17 04:34:43Z

Try like below with Gson Library.

Earlier Conversion List format were:

[Product [Id=1, City=Bengalore, Category=TV, Brand=Samsung, Name=Samsung LED, Type=LED, Size=32 inches, Price=33500.5, Stock=17.0], Product [Id=2, City=Bengalore, Category=TV, Brand=Samsung, Name=Samsung LED, Type=LED, Size=42 inches, Price=41850.0, Stock=9.0]]

and here the conversion source begins.

//** Note I have created the method toString() in Product class.

//Creating and initializing a java.util.List of Product objects
List<Product> productList = (List<Product>)productRepository.findAll();

//Creating a blank List of Gson library JsonObject
List<JsonObject> entities = new ArrayList<JsonObject>();

//Simply printing productList size
System.out.println("Size of productList is : " + productList.size());

//Creating a Iterator for productList
Iterator<Product> iterator = productList.iterator();

//Run while loop till Product Object exists.
while(iterator.hasNext()){

    //Creating a fresh Gson Object
    Gson gs = new Gson();

    //Converting our Product Object to JsonElement 
    //Object by passing the Product Object String value (iterator.next())
    JsonElement element = gs.fromJson (gs.toJson(iterator.next()), JsonElement.class);

    //Creating JsonObject from JsonElement
    JsonObject jsonObject = element.getAsJsonObject();

    //Collecting the JsonObject to List
    entities.add(jsonObject);

}

//Do what you want to do with Array of JsonObject
System.out.println(entities);

Converted Json Result is :

[{"Id":1,"City":"Bengalore","Category":"TV","Brand":"Samsung","Name":"Samsung LED","Type":"LED","Size":"32 inches","Price":33500.5,"Stock":17.0}, {"Id":2,"City":"Bengalore","Category":"TV","Brand":"Samsung","Name":"Samsung LED","Type":"LED","Size":"42 inches","Price":41850.0,"Stock":9.0}]

Hope this would help many guys!

Rasanjana N · Accepted Answer · 2019-03-28 06:24:42Z

0

JSONObject responseDetailsJson = new JSONObject();
JSONArray jsonArray = new JSONArray();

List<String> ls =new  ArrayList<String>();

for(product cj:cities.getList()) {
    ls.add(cj);
    JSONObject formDetailsJson = new JSONObject();
    formDetailsJson.put("id", cj.id);
    formDetailsJson.put("name", cj.name);
    jsonArray.put(formDetailsJson);
}

responseDetailsJson.put("Cities", jsonArray);

return responseDetailsJson;

edited Mar 28, 2019 at 6:24

Rasanjana N

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answered Mar 28, 2019 at 5:53

vipin kumar

1

Comments

Sollymanul Islam · Accepted Answer · 2020-10-20 15:01:00Z

0

You can use the following method which uses Jackson library

public static <T> List<T> convertToList(String jsonString, Class<T> target) {
    if(StringUtils.isEmpty(jsonString)) return List.of();

        return new ObjectMapper().readValue(jsonString, new ObjectMapper().getTypeFactory().
                constructCollectionType(List.class, target));
    } catch ( JsonProcessingException | JSONException e) {
        e.printStackTrace();
        return List.of();
    }
}

edited Oct 20, 2020 at 15:01

answered Oct 20, 2020 at 14:51

Sollymanul Islam

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Comments

Abhiram Chowdary · Accepted Answer · 2022-03-20 15:52:24Z

-1

if response is of type List , res.toString() is simply enough to convert to json or else we need to use ObjectMapper mapper = new ObjectMapper(); String jsonRes = mapper.writeValueAsString(res);

edited Mar 20, 2022 at 15:52

answered Mar 15, 2022 at 6:39

Abhiram Chowdary

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