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/UserServiceMapImpl.java

@@ -0,0 +1,68 @@
+package com.baeldung.sparkjava;
+
+import java.util.Collection;
+import java.util.HashMap;
+
+public class UserServiceMapImpl  implements UserService{
+    private HashMap<String, User> userMap;
+    
+    public UserServiceMapImpl() {
+        userMap = new HashMap<>();
+    }
+
+    @Override
+    public void addUser (User user) {
+        userMap.put(user.getId(), user);
+    }
+    
+    @Override
+    public Collection<User> getUsers () {
+        return  userMap.values();
+    }
+    
+    @Override
+    public User getUser (String id) {
+        return userMap.get(id);
+    }
+    
+    @Override
+    public User editUser (User forEdit) throws UserException{
+        try{
+            if (forEdit.getId() == null) 
+                throw new UserException("ID cannot be blank");
+            
+            User toEdit = userMap.get(forEdit.getId());
+            
+            if (toEdit == null )
+                throw new UserException("User not found");
+            
+            if (forEdit.getEmail()!=null) {
+                toEdit.setEmail(forEdit.getEmail());
+            }
+            if (forEdit.getFirstName()!=null) {
+                toEdit.setFirstName(forEdit.getFirstName());
+            }
+            if (forEdit.getLastName()!=null) {
+                toEdit.setLastName(forEdit.getLastName());
+            }
+            if (forEdit.getId()!=null) {
+                toEdit.setId(forEdit.getId());
+            }
+
+            return toEdit;
+        }catch (Exception ex) {
+            throw new UserException(ex.getMessage());
+        }
+    }
+    
+    @Override
+    public void deleteUser (String id) {
+        userMap.remove(id);
+    }
+    
+    @Override
+    public boolean userExist (String id) {
+        return userMap.containsKey(id);
+    }
+
+}