如何在Java中将List转换为Json

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.

Answer 1

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);

Answer 2

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.

Answer 3

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

Answer 4

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 .

Answer 5

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

Answer 6

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

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

Answer 7

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>

Answer 8

Use GSONBuilder with setPrettyPrinting and disableHtml for nice output.

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