Spark Java Article BAEL-498 (#912)

* Initial Commit for Spark Java Article BAEL-498

* reverting main pom.xml and rollbacking accidental changes.

* Changes as per review:

1. Added UserService
2. Renamed UserStore to UserServiceMapImpl
3. Removed Empty spaces in User.java
4. Removed AppTest
5. Changes in SparkRestExample for using UserServiceMapImp instead of
UserStore static functions.

* Suggested changes in print messages.

* Changes as per comments on github... for PR:
https://github.com/eugenp/tutorials/pull/912

* Changes in editUser function as per guidance by Kevin.

* Clean up

* added 1.8 config for pom.xml

* Clean up.

* Removed junit dep.

* Added Application/json in response type.

spark-java/src/main/java/com/baeldung/sparkjava/SparkRestExample.java

@@ -0,0 +1,76 @@
+package com.baeldung.sparkjava;
+
+import static spark.Spark.delete;
+import static spark.Spark.get;
+import static spark.Spark.options;
+import static spark.Spark.post;
+import static spark.Spark.put;
+
+import com.google.gson.Gson;
+
+public class SparkRestExample {
+    public static void main(String[] args) {
+        final UserService userService = new UserServiceMapImpl();
+        
+        post("/users", (request, response) -> {
+            response.type("application/json");
+            
+            User user = new Gson().fromJson(request.body(), User.class);
+            userService.addUser(user);
+
+            return new Gson().toJson(new StandardResponse(StatusResponse.SUCCESS));
+        });
+
+        get("/users", (request, response) -> {
+            response.type("application/json");
+            
+            return new Gson().toJson(
+                new StandardResponse(StatusResponse.SUCCESS,new Gson()
+                    .toJsonTree(userService.getUsers())));
+        });
+
+        get("/users/:id", (request, response) -> {
+            response.type("application/json");
+            
+            return new Gson().toJson(
+                new StandardResponse(StatusResponse.SUCCESS,new Gson()
+                  .toJsonTree(userService.getUser(request.params(":id")))));
+        });
+
+        put("/users/:id", (request, response) -> {
+            response.type("application/json");
+            
+            User toEdit = new Gson().fromJson(request.body(), User.class);
+            User editedUser = userService.editUser(toEdit);
+                
+            if (editedUser != null) {
+                return new Gson().toJson(
+                    new StandardResponse(StatusResponse.SUCCESS,new Gson()
+                        .toJsonTree(editedUser)));
+            }else  {
+                return new Gson().toJson(
+                    new StandardResponse(StatusResponse.ERROR,new Gson()
+                        .toJson("User not found or error in edit")));
+            }
+        });
+
+        delete("/users/:id", (request, response) -> {
+            response.type("application/json");
+            
+            userService.deleteUser(request.params(":id"));
+            return new Gson().toJson(
+                new StandardResponse(StatusResponse.SUCCESS, "user deleted"));
+        });
+
+        options("/users/:id", (request, response) -> {
+            response.type("application/json");
+            
+            return new Gson().toJson(
+                new StandardResponse(StatusResponse.SUCCESS, 
+                    (userService.userExist(
+                        request.params(":id"))) ? "User exists" : "User does not exists" ));
+        });
+
+    }
+
+}