Sending Json [Gson implementation] from Rest-Webservice

Question

I am using Gson library to handle parsing Json to java entities and vice-versa. Now, after processing the in need to return the Json object to the caller. But doing so results in following exception:

Mar 25, 2014 4:46:30 PM com.sun.jersey.spi.container.ContainerResponse write
SEVERE: A message body writer for Java class com.google.gson.JsonObject, and Java type class com.google.gson.JsonObject, and MIME media type application/json was not found
Mar 25, 2014 4:46:30 PM com.sun.jersey.spi.container.ContainerResponse write
SEVERE: The registered message body writers compatible with the MIME media type are:

Json after processing is {"status":"Entity added successfully."}

My Observation: It seems like i need to register Gson implementation for Json somewhere to let the container know that I will send Json data using Gson's JsonObject. If i observed correctly, then where should i register and how, or if i am totally wrong then, please correct me.

My implementation looks like following:

@POST
@Path("/entity")
@Produces(MediaType.APPLICATION_JSON)
public Response addEntity(@FormParam("entity") String jsonEntity, @FormParam("entityType") String jsonEntityType) {
    JsonObject jSonStatus = null;
    log.info("Entered webservice method: " + jsonEntity.toString() + "\n" + jsonEntityType.toString());
    if (jsonEntity != null && jsonEntityType != null) {
        dispatcher = dispatcher.getDispatcher();
        jSonStatus = dispatcher.addEntity(jsonEntity, jsonEntityType);
    }
    log.info("Returning from webservice method: " + jSonStatus);
    ResponseBuilder rb = new ResponseBuilderImpl();
    // rb.type(MediaType.APPLICATION_JSON);   tried with this also, but no luck
    rb.entity(jSonStatus);
    rb.status(Status.OK);

    return rb.build();
}

One option i can think of is returning normal `String` as json is nothing but organised `String`. — Gaurav Gupta, Mar 25 '14 at 11:46
Please check this answer: http://stackoverflow.com/questions/9516224/using-gson-instead-of-jackson-in-jersey — Wintermute, Mar 25 '14 at 11:50
@Wintermute Suggested link guided me to right direction, but is their any reference doc too for the implementation apart from javadoc if the `Writer` classes mentioned in the link — Gaurav Gupta, Mar 25 '14 at 12:16

score 1 · Accepted Answer · answered Mar 26 '14 at 13:18

I figured out the usage of 'MessageBodyReader' and 'MessageBodyWriter' and i found that need of implementing these two interfaces was just to put the parsing logic separate from the core business logic. Since i already had parser implemented for me, so i had to shift my parse code to take advantage of interfaces.

So, i decided to return the String and set the response type as Json, since i had Json string already available after processing.

So now my code looks like:

    @Produces(MediaType.APPLICATION_JSON)
    public String addEntity(@FormParam("entity") String jsonEntity, @FormParam("entityType") String jsonEntityType) {
        JsonObject jSonStatus = null;
        ....
        ....    
        return JsonStatus.toString;
}

To checked the response in Advance Rest client, it showed correct Json with Content-Type: application/json

Note: Please comment if i am not taking care of something important.

Sending Json [Gson implementation] from Rest-Webservice

1 Answers1