How do I expose data in a JSON format through a web service using Java?

Question

Is there an easy way to return data to web service clients in JSON using java? I'm fine with servlets, spring, etc.

Answer 1

It might be worth looking into Jersey. Jersey makes it easy to expose restful web services as xml and/or JSON.

An example... start with a simple class

@XmlType(name = "", propOrder = { "id", "text" }) @XmlRootElement(name = "blah") public class Blah implements Serializable {     private Integer id;     private String text;      public Blah(Integer id, String text) {         this.id = id;         this.text = text;     }          @XmlElement     public Integer getId() { return id; }     public void setId(Integer id) { this.id = id; }      @XmlElement     public String getText() { return text; }     public void setText(String value) { this.text = value; } } 

Then create a Resource

@Path("/blah") public class BlahResource {     private Set<Blah> blahs = new HashSet<Blah>();      @Context     private UriInfo context;      public BlahResource() {         blahs.add(new Blah(1, "blah the first"));         blahs.add(new Blah(2, "blah the second"));     }      @GET     @Path("/{id}")     @ProduceMime({"application/json", "application/xml"})     public Blah getBlah(@PathParam("id") Integer id) {         for (Blah blah : blahs) {             if (blah.getId().equals(id)) {                 return blah;             }         }         throw new NotFoundException("not found");     } } 

and expose it. There are many ways to do this, such as by using Jersey's ServletContainer. (web.xml)

<servlet>     <servlet-name>jersey</servlet-name>     <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>     <load-on-startup>1</load-on-startup> </servlet>  <servlet-mapping>     <servlet-name>jersey</servlet-name>     <url-pattern>/*</url-pattern> </servlet-mapping> 

Thats all you need to do... pop open your browser and browse to http://localhost/blah/1. By default you will see XML output. If you are using FireFox, install TamperData and change your accept header to application/json to see the JSON output.

Obviously there is much more to it, but Jersey makes all that stuff quite easy.

Good luck!

Answer 2

We have been using Flexjson for converting Java objects to JSON and have found it very easy to use. http://flexjson.sourceforge.net

Here are some examples:

public String searchCars() {   List<Car> cars = carsService.getCars(manufacturerId);   return new JSONSerializer().serialize(cars); } 

It has some cool features such as deepSerialize to send the entire graph and it doesn't break with bi directional relationships.

new JSONSerializer().deepSerialize(user);  

Formatting dates on the server side is often handy too

new JSONSerializer().transform(   new DateTransformer("dd/MM/yyyy"),"startDate","endDate" ).serialize(contract);