Merge pull request #9 from eugenp/master

update with origin

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

@@ -0,0 +1,17 @@
+package com.baeldung.sparkjava;
+
+import java.util.Collection;
+
+public interface UserService {
+    public void addUser(User user);
+
+    public Collection<User> getUsers();
+
+    public User getUser(String id);
+
+    public User editUser(User user) throws UserException;
+
+    public void deleteUser(String id);
+
+    public boolean userExist(String id);
+}