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>>(){});

This works. Added []. I used

payload = objectMapper.readValue(jsonFile, objectMapper.getTypeFactory().constructCollectionType(List.class, Pojo.class));

for the conversion.

App.java

public class App {

    public static void main(String[] args) {
        String jsonFile = "[{\"name\":\"test\",\"value\":\"8893\"},\n" +
                "{\"name\":\"test2\",\"value\":\"1\"},\n" +
                "{\"name\":\"test3\",\"value\":\"68\"},\n" +
                "{\"name\":\"test4\",\"value\":\"26824212473\"}]";

        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.writerWithDefaultPrettyPrinter();

        List<Pojo> payload = null;

        try {
            payload = objectMapper.readValue(jsonFile, objectMapper.getTypeFactory().constructCollectionType(List.class, Pojo.class));
        } catch (IOException e) {
            e.printStackTrace();
        }

        payload.forEach(System.out::println);

    }

}

Pojo.java

class Pojo {
    private String name;
    private String value;

    public Pojo() {
        super();
    }

    public Pojo(String name, String value) {
        this.name = name;
        this.value = value;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "Pojo{" +
                "name='" + name + '\'' +
                ", value='" + value + '\'' +
                '}';
    }
}

This format of json is not Appropriate.you can change format and use array for sequential keys. but you can use below approach:

JSONObject object = new JSONObject(message);
Iterator<String> keyList = object.keys();

while (keyList.hasNext()){
     String key = keyList.next();
     object.get(key);
     //parse value and use it

}

Definitely the easiest way to do that is using Gson's default parsing function fromJson().

There is an implementation of this function suitable for when you need to deserialize into any ParameterizedType (e.g., any List), which is fromJson(JsonElement json, Type typeOfT).

In your case, you just need to get the Type of a List<String> and then parse the JSON array into that Type, like this:

import java.lang.reflect.Type;
import com.google.gson.reflect.TypeToken;

JsonElement yourJson = mapping.get("servers");
Type listType = new TypeToken<List<String>>() {}.getType();

List<String> yourList = new Gson().fromJson(yourJson, listType);

In your case yourJson is a JsonElement, but it could also be a String, any Reader or a JsonReader.

You may want to take a look at Gson API documentation.

The JSON should have a root node.

If you don't have that, you can read from the file line-by-line, and pass each line into the JSONParser wrapped in a StringReader (since the JSONParser.parse() method takes a Reader).

e.g.

   BufferedReader in
      = new BufferedReader(new FileReader("test.json"));
   while(!done) {
      String s = in.readLine();
      if (s == null) {
         done = true;
      }
      else {
         StringReader sr = new StringReader(s);
         // etc...
      }
   }

Edit: I've assumed you're using JSONParser. If you're using a different parser (which one?) then it may take a String argument.

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);