How to Convert List to JSON in Java

How to convert List to Json in Java

Use GSON library for that. Here is the sample code

List<String> foo = new ArrayList<String>();
foo.add("A");
foo.add("B");
foo.add("C");

String json = new Gson().toJson(foo );

Here is the maven dependency for Gson

<dependencies>
    <!--  Gson: Java to Json conversion -->
    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.2.2</version>
        <scope>compile</scope>
    </dependency>
</dependencies>

Or you can directly download jar from here and put it in your class path

http://code.google.com/p/google-gson/downloads/detail?name=gson-1.0.jar&can=4&q=

To send Json to client you can use spring or in simple servlet add this code

response.getWriter().write(json);

How to convert list data into json in java

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" } 
    ]
}

Convert List to JsonObject in Java using json simple

Got the answer -

First converted the List to Map and then to Json -

public Map<String, String> test() {

    Map<String, String> result = items.stream().collect(Collectors.toMap(Item::getValue, Item::getType)); //Converts List items to Map

    System.out.println("Result  : " + result);

    JSONObject json = new JSONObject(result); //Converts MAP to JsonObject

    System.out.println("JSON : " + json); //prints {"firstname":"abc","lastname":"pqr","id":"1"}
    return result;
}

Convert list of Objects to JSON Array in java - Spring Boot api testing

It seems to me that the issue is that you are trying to pass something like the following JSON to the content:

[
  {
    "compania1_list": "Compania1 list",
    "name1": "name1",
    "s": "---",
    "s1": "---",
    "o": null,
    "o1": null
  },
  {
    "compania1_list": "Compania2 list",
    "name1": "name2",
    "s": "---",
    "s1": "---",
    "o": null,
    "o1": null
  }
]

This is a JSON Array with 2 JSON Objects and not a JSON Object with a JSON Array with 2 JSON Objects. My guess is that MockHttpServletRequestBuilder.content() method is not expecting JSON like this.

With this being said, I would change your Controller to accept an Object and not a Collection as follows:

@ResponseStatus(HttpStatus.CREATED)
@PostMapping("/lista")
public Map<String, Object> createCompanias(@RequestBody CompaniasCreationRequest companiasCreationRequest) {
    return companiaService.postListCompanias(companiasCreationRequest.getCompanias());
}

Being CompaniasCreationRequest as follows:

public class CompaniasCreationRequest {
    private List<Compania> companias;

    public CompaniasCreationRequest(List<Compania> companias) {
        this.companias = companias;
    }

    public List<Compania> getCompanias() {
        return companias;
    }

    public void setCompanias(List<Compania> companias) {
        this.companias = companias;
    }
}

In your test this would mean the following changes:

@Test
void successSavePostCompaniaLista() throws Exception {
    Compania c1 = new Compania("Compania1 list",
        "name1",
        "---",
        "---",
        null,
        null);
    Compania c2 = new Compania("Compania2 list",
        "name2",
        "---",
        "---",
        null,
        null);

    CompaniasCreationRequest companiasCreationRequest = new CompaniasCreationRequest(List.of(c1,c2));
    
    when(companiaRepository.save(any(Compania.class))).then(returnsFirstArg());

    this.mockMvc.perform(
            post("/companias/lista")
                .header("authorization", "Bearer " + token)
                .content(asJsonString(companiasCreationRequest))
                .contentType(MediaType.APPLICATION_JSON))
        .andDo(print())
        .andExpect(status().isCreated())
        .andExpect(jsonPath("$.result[0].success[0]").isNotEmpty())
        .andExpect(jsonPath("$.result[0].success[0].name").value(c1.getName()))
        .andExpect(jsonPath("$.result[0].success[1].name").value(c2.getName()));
}

Now your request body will look like the following (which is a somewhat more standard JSON format):

{
  "companias": [
    {
      "compania1_list": "Compania1 list",
      "name1": "name1",
      "s": "---",
      "s1": "---",
      "o": null,
      "o1": null
    },
    {
      "compania1_list": "Compania2 list",
      "name1": "name2",
      "s": "---",
      "s1": "---",
      "o": null,
      "o1": null
    }
  ]
}

How to convert JSON string into List of Java object?

You are asking Jackson to parse a StudentList. Tell it to parse a List (of students) instead. Since List is generic you will typically use a TypeReference

List<Student> participantJsonList = mapper.readValue(jsonString, new TypeReference<List<Student>>(){});

How to convert an Array List of objects to Json

Play comes with play-json module which can do it. You might have to create a wrapping class to output the kunden root node:

public class Kunden {
  private List<Kunde> kunden;
  // getter and setter
}

Kunden root = new Kunden();
kunden.setKunden(...);

JsonNode rootNode = Json.toJson(root);
ObjectMapper mapper = new ObjectMapper(); 
String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(node);

Note that ObjectMapper is used to pretty print.

See the official Play Framework 2.6.X docs: Mapping Java objects to JSON.

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