How to convert List to Json in Java

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.

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);

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.

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>

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.

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

download java-json.jar from Java2s <Http://www.java2s.com/Code/Jar/j/Downloadjavajsonjar.htm> then use the JSONArray constructor

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

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

Use GSONBuilder with setPrettyPrinting and disableHtml for nice output.

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