sending arraylist from a rest service - json

Question

I am new to webservices and also REST. I am trying to send a message as a post request to a rest service using rest java client.I am trying to get response of previous requests also(everything in json format). So, am storing the message objects into an arraylist and sending the list as a reponse. But I am not able to get the previous messages. Please tell me if am doing anything wrong.
This is my message model class.
public class Messages {
private String id;
private String message;
public Messages() {
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
the following is my webservice to receive a message object and return a json array.
#Path("/json/messages")
public class JSONMessages {
public List<Messages> list = new ArrayList<Messages>();
List<Messages> getAllMessages(Messages m){
list.add(m);
return list;
}
#POST
#Path("/post")
#Consumes(MediaType.APPLICATION_JSON)
#Produces(MediaType.APPLICATION_JSON)
public Response MessageListInJSON(Messages msg) {
System.out.println("message saved");
if(!(msg.getId().equals("1"))){
String output ="Invalid User";
return Response.ok(output).build();
}
else{
return Response.ok(getAllMessages(msg)).build();
}
}
}
Finally, the following is my client side code
public class ClientPost {
public static void main(String[] args) {
try {
ClientConfig clientConfig = new DefaultClientConfig();
Client client = Client.create(clientConfig);
WebResource webResource = client
.resource("http://localhost:8050/lab.rest.webservices/rest/json/messages/post");
//for(int i=0;i<5;i++){
String input = "{\"id\":\"1\", \"message\":\"hey there!\"}";
ClientResponse response = webResource.accept("application/json").type("application/json")
.entity(input).post(ClientResponse.class);
if (response.getStatus() !=200 ) {
throw new RuntimeException("Failed : HTTP error code : "
+ response.getStatus());
}
System.out.println("Output from Server .... \n");
String output = response.getEntity(String.class);
System.out.println(output+"\n");
}
catch (Exception e) {
e.printStackTrace();
}
} }
Now, what I am expecting to see is the message I sent along with the previous responses stored in the array list(which were sent by running the client multiple times manually for now) but always am ending up with only the current message.
output:
Output from Server ....
[{"id":"1","message":"hey there!"}]
To be precise, what I want as output when i run my client several times(or put the try block in loop) is as follows which i am unable to get.
Output from Server ....
[{"id":"1","message":"hey there!"},{"id":"1","message":"hey there!"},{"id":"1","message":"hey there!"},{"id":"1","message":"hey there!"}] .

Answer 1

Resources in JAXRS aren't singletons. That means that for each request, the class JSONMessages is instantiated. So you lose the content of the attribute list. Changing it to static could fix your problem.
There is an annotation Singleton to change this behavior. In this case the resource will be managed as singleton and not in request scope. Here is a sample:
#Singleton
#Path("/json/messages")
public class JSONMessages {
(...)
}
Otherwise, be careful of concurrent accesses on your list. See this question for more details: java concurrent Array List access.
Hope it helps you,
Thierry