Convert Java Object to Json and Vice versa?

Question

I know that JSON object is nothing but the String .

My question is that I have a Map of Object and i want to convert it into Json format.

Example :

Java Class ->
Class Person{
  private String name;
  private String password;
  private int number;
}

Java list ->
Map<List<Long>,List<Person>> map=new HashMap<List<Long>,List<Person>>();
..and map has Some data filled in it.

I want to convert that list into

 Json Format?

How I can achieve it? Because i want to send it over HttpClient... If not what is the other alternative way?

As per my knowledge there is Gson API available, but I dont know how to use it and or in other efficient way.

Thank you

Answer 1

Not sure what the problem with Gson is. From the doc :

BagOfPrimitives obj = new BagOfPrimitives();
Gson gson = new Gson();
String json = gson.toJson(obj); 

and

BagOfPrimitives obj2 = gson.fromJson(json, BagOfPrimitives.class);  

That object is (as the name suggests) made up of primitives. However Gson will trivially handle objects, collections of objects etc. Life gets a little more complex when using generics etc., but for your example above I would expect Gson to work with little trouble.

Answer 2

Using Gson to convert to Json using Gson at client side.

Sending String array.

    String[] subscriberArray = new String[]{"eee", "bbb"}; 
    Gson gson = new Gson();
    String recipientInfoStringFormat = gson.toJson(subscriberArray);    

Sending Array of User Defined Type.

        RecipientInfo[] recipientInfos = new RecipientInfo[1];

        RecipientInfo ri = new RecipientInfo();
        ri.setA(1);
        ri.setB("ss");

        recipientInfos.add(ri);

        Gson gson = new Gson();
        String recipientInfoStringFormat = gson.toJson(recipientInfos);     

Using Gson at Server Side to read Data.

For Primitive Types.

            String subscriberArrayParam = req.getParameter("subscriberArrayParam"); 
    Gson gson = new Gson();
    String[] subscriberArray = gson.fromJson(subscriberArrayParam, String[].class);     
    for (String str : subscriberArray) {
        System.out.println("qq :"+str);
    }

For User Defined Object

    String recipientInfos = req.getParameter("recipientInfoStringFormat");

    Gson gson = new Gson();
    RecipientInfo[] ri = gson.fromJson(recipientInfos, RecipientInfo[].class);  

Answer 3

You can use jackson also.

    Person person= new Person();
ObjectMapper mapper = new ObjectMapper();

try {

    // convert personobject to json string, and save to a file
    mapper.writeValue(new File("c:\\person.json"), person);

    // display to console
    System.out.println(mapper.writeValueAsString(person));

} catch (Exception e) {

    e.printStackTrace();

} 

and vice versa

    ObjectMapper mapper = new ObjectMapper();

try {

    // read from file, convert it to user class
    Person person= mapper.readValue(new File("c:\\person.json"), Person.class);

    // display to console
    System.out.println(person);

} catch (Exception e) {

    e.printStackTrace();

}

for using jackson add this dependency to your POM.xml

<repositories>
<repository>
    <id>codehaus</id>
    <url>http://repository.codehaus.org/org/codehaus</url>
</repository>
</repositories>

<dependencies>
<dependency>
    <groupId>org.codehaus.jackson</groupId>
    <artifactId>jackson-mapper-asl</artifactId>
    <version>1.8.5</version>
</dependency>
</dependencies>

Answer 4

I got my Answer but Thank you for Your Responses.

 Map<Long,List<Person>> map=new HashMap<Long,List<Person>>();
    //adding some data

Gson gson=new Gson();
String mapJsonStr=gson.toJson(map);

//mapJsonStr : is my map's JSon Strin

for reverse

 TypeToken<Map<Long,List<Person>>> token = new TypeToken<Map<Long,List<Person>>>(){};
    Map<Long,List<Person>> map_new=new HashMap<Long,List<Person>>();
    map_new=gson.fromJson(mapJsonStr,token.getType());

    //origian map
// map_new is my Map get from map's Json String

That's It.Thank you