How to convert List to Json in Java

Question

How to convert generic list to json in Java.I have class like this..

public class Output
{
    public int Keyname { get; set; }
    public Object  outputvalue{ get; set; }  //outvalue may be even a object collection
}

List<Output> outputList = new List<Output>();

I want to convert outputList into json in Java.After converting i will send it to client.

Thats rather difficult if you just know the outputvalue is an `Object`. We can not even assume it is serializable. — Henry, Jan 09 '13 at 05:45
possible duplicate of [how to convert a List of Data to json](http://stackoverflow.com/questions/8182391/how-to-convert-a-list-of-data-to-json) — Gabriel, Jan 09 '13 at 05:47
Can you tell us what framwork that you use, such as spring or something else, in some framework that it can do this automatically, and send data to the client browser. — OQJF, Jan 09 '13 at 05:51
You can use GSON like this >> http://stackoverflow.com/a/15332888/3920648 it work for me — Telember, Jan 18 '15 at 15:16

score 150 · Accepted Answer · edited Aug 28 '15 at 15:03

150

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);

edited Aug 28 '15 at 15:03

Mr. Polywhirl

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answered Jan 09 '13 at 05:50

code_fish

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How to remove null from the json if the list contain null. – rahul Jan 09 '14 at 07:15
How does the output look like? – AlikElzin-kilaka Feb 25 '14 at 16:19
1

You should write `new ArrayList<>()` instead of `new ArrayList()`. – principal-ideal-domain May 12 '15 at 08:41

Rahul · Answer 2 · 2013-01-09T05:50:16.067

14

You need an external library for this.

JSONArray jsonA = JSONArray.fromObject(mybeanList);
System.out.println(jsonA);

Google GSON is one of such libraries

You can also take a look here for examples on converting Java object collection to JSON string.

edited Jan 09 '13 at 05:50

answered Jan 09 '13 at 05:43

Rahul

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score 7 · Answer 3 · answered May 10 '18 at 14:58

jackson provides very helpful and lightweight API to convert Object to JSON and vise versa. Please find the example code below to perform the operation

List<Output> outputList = new ArrayList<Output>();
public static void main(String[] args) {
    try {
        Output output = new Output(1,"2342");
        ObjectMapper objectMapper = new ObjectMapper();
        String jsonString = objectMapper.writeValueAsString(output);
        System.out.println(jsonString);
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }
}

there are many other features and nice documentation for Jackson API. you can refer to the links like: https://www.journaldev.com/2324/jackson-json-java-parser-api-example-tutorial..

dependencies to include in the project are

    <!-- Jackson -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.5.1</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.5.1</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.5.1</version>
    </dependency>

score 4 · Answer 4 · answered Jan 09 '13 at 07:34

Try this:

public void test(){
// net.sf.json.JSONObject, net.sf.json.JSONArray    

List objList = new ArrayList();
objList.add("obj1");
objList.add("obj2");
objList.add("obj3");
HashMap objMap = new HashMap();
objMap.put("key1", "value1");
objMap.put("key2", "value2");
objMap.put("key3", "value3");
System.out.println("JSONArray :: "+(JSONArray)JSONSerializer.toJSON(objList));
System.out.println("JSONObject :: "+(JSONObject)JSONSerializer.toJSON(objMap));
}

you can find API here.

score 3 · Answer 5 · answered Jan 09 '13 at 05:45

3

Look at the google gson library. It provides a rich api for dealing with this and is very straightforward to use.

answered Jan 09 '13 at 05:45

Dave G

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@vbm - https://sites.google.com/site/gson/gson-user-guide#TOC-Collections-Examples – Stephen C Jan 09 '13 at 06:25

score 3 · Answer 6 · answered May 10 '18 at 14:39

3

download java-json.jar from Java2s then use the JSONArray constructor

List myList = new ArrayList<>();    
JSONArray jsonArray = new JSONArray(myList);
System.out.println(jsonArray);

answered May 10 '18 at 14:39

Ali

71
2

score 2 · Answer 7 · answered Aug 28 '15 at 15:23

For simplicity and well structured sake, use SpringMVC. It's just so simple.

@RequestMapping("/carlist.json")
public @ResponseBody List<String> getCarList() {
    return carService.getAllCars();
}

Reference and credit: https://github.com/xvitcoder/spring-mvc-angularjs

score -1 · Answer 8 · answered Oct 13 '17 at 00:52

-1

Use GSONBuilder with setPrettyPrinting and disableHtml for nice output.

String json = new GsonBuilder().setPrettyPrinting().disableHtmlEscaping().
                            create().toJson(outputList  );
                    fileOut.println(json);

answered Oct 13 '17 at 00:52

Ammad

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How to convert List to Json in Java

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