technology

Custom marshalling with Gson - part 1

Today, I’ll extend our project to add temporary storage of uploaded users in a HashMap<String,User> and allow retrieval of that HashMap as json. First, the new UserMap class. This class will be needed to register custom marshalling. 

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package com.ideoplex.tutorial;

import java.util.concurrent.ConcurrentHashMap;


public class UserMap extends ConcurrentHashMap<String,User> {
}

And three changes to the MyResource class. First, a static UserMap member to store the uploaded users. Second, a new getUserMap method to return the static member. And finally, an update to the postUser method to throw a WebApplicationException when uploading a duplicate email address and add the user to the static UserMap otherwise. 

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diff --git a/src/main/java/com/ideoplex/tutorial/MyResource.java b/src/main/java/com/ideoplex/tutorial/MyResource.java
index 8a932e5..60f818f 100644
--- a/src/main/java/com/ideoplex/tutorial/MyResource.java
+++ b/src/main/java/com/ideoplex/tutorial/MyResource.java
@@ -5,6 +5,8 @@ import javax.ws.rs.POST;
 import javax.ws.rs.Path;
 import javax.ws.rs.Consumes;
 import javax.ws.rs.Produces;
+import javax.ws.rs.WebApplicationException;
+import javax.ws.rs.core.Response;
 import javax.ws.rs.core.MediaType;
 
 /**
@@ -12,6 +14,10 @@
  */
 @Path("myresource")
 public class MyResource {
+    /**
+     * HashMap<String,User> containing all Users known to the system
+     */
+    protected static UserMap users = new UserMap();
 
     /**
      * Method handling HTTP GET requests. The returned object will be sent
@@ -26,6 +32,16 @@ public class MyResource {
     }
 
     /**
+     */
+    @GET
+    @Path("user/map")
+    @Produces(MediaType.APPLICATION_JSON)
+    public UserMap getUserMap()
+    {
+        return users;
+    }
+
+    /**
      * Methods to get and post a json User object
      */
     @GET
@@ -43,6 +59,17 @@ public class MyResource {
     @Path("user/post")
     @Consumes(MediaType.APPLICATION_JSON)
     public User postUser(User user) {
-        return user;
+        String email = user.getEmail();
+        if ( users.containsKey(email) ) {
+            throw new WebApplicationException(Response
+                                              .status(Response.Status.BAD_REQUEST)
+                                              .type(MediaType.TEXT_PLAIN)
+                                              .entity("User email \"" + email + "\" already exists")
+                                              .build());
+        }
+        else {
+            users.put(email, user);
+            return user;
+        }
     }
 }

Run mvn install to deploy the new web application and then I can post our first user to the webapp. 

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$ curl http://xxxxxx-nnnnnn.use1-2.nitrousbox.com:8080/jersey-gson/webapi/myresource/user/post \
 --header 'Content-type: application/json' \
 --data '{"email":"noone@example.com","surName":"Doe","givenName":"John"}'
{"email":"noone@example.com","surName":"Doe","givenName":"John"}

My attempt to post the same email address again fails. 

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$ curl http://xxxxxx-nnnnnn.use1-2.nitrousbox.com:8080/jersey-gson/webapi/myresource/user/post \
 --header 'Content-type: application/json' \
 --data '{"email":"noone@example.com","surName":"Doe","givenName":"John"}'
User email "noone@example.com" already exists

I post a second user. 

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$ curl http://xxxxxx-nnnnnn.use1-2.nitrousbox.com:8080/jersey-gson/webapi/myresource/user/post \
 --header 'Content-type: application/json' \
 --data '{"email":"john@example.com","surName":"Public","givenName":"John"}'
{"email":"john@example.com","surName":"Public","givenName":"John"}

And I retrieve the user map – with a little formatting for clarity: 

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$ curl http://xxxxxx-nnnnnn.use1-2.nitrousbox.com:8080/jersey-gson/webapi/myresource/user/map
{"john@example.com":{"email":"john@example.com","surName":"Public","givenName":"John"},
 "noone@example.com":{"email":"noone@example.com","surName":"Doe","givenName":"John"}
}

I’ll continue this post tomorrow. Meanwhile, you can browse the source for jersey-gson on GitHub.

28 Sep: Jersey and Gson
30 Sep Custom marshalling with Gson - part 2