simple error handling

service/src/main/java/com/telephoners/krakyournet/ctf/exceptions/ElementAlreadyExistsException.java

+package com.telephoners.krakyournet.ctf.exceptions;
+
+import com.telephoners.krakyournet.ctf.beans.User;
+
+import javax.ws.rs.WebApplicationException;
+import javax.ws.rs.core.Response;
+
+public class ElementAlreadyExistsException extends WebApplicationException
+{
+    public ElementAlreadyExistsException(final Class<User> elementName)
+    {
+        super(Response.status(Response.Status.BAD_REQUEST)
+                .entity(String.format("Element %s already exists", elementName.getSimpleName()))
+                .type("text/plain")
+                .build());
+    }
+}

service/src/main/java/com/telephoners/krakyournet/ctf/exceptions/ElementDoesNotExistException.java

+package com.telephoners.krakyournet.ctf.exceptions;
+
+import com.telephoners.krakyournet.ctf.beans.Team;
+
+import javax.ws.rs.WebApplicationException;
+import javax.ws.rs.core.Response;
+
+public class ElementDoesNotExistException extends WebApplicationException
+{
+    public ElementDoesNotExistException(final Class<Team> elementName)
+    {
+        super(Response.status(Response.Status.NOT_FOUND)
+                .entity(String.format("Element %s does not exist", elementName.getSimpleName()))
+                .type("text/plain")
+                .build());
+    }
+}

service/src/main/java/com/telephoners/krakyournet/ctf/repositories/UserRepository.java

+package com.telephoners.krakyournet.ctf.repositories;
+
+import com.google.inject.Inject;
+import com.telephoners.krakyournet.ctf.beans.User;
+import com.telephoners.krakyournet.ctf.core.DataConnector;
+
+public class UserRepository extends Repository<User>
+{
+    @Inject
+    public UserRepository(final Class<User> type, final DataConnector<User> connector)
+    {
+        super(type, connector);
+    }
+
+    //todo: this should be handled by driver itself
+    public boolean exists(final String userName)
+    {
+        return getAll()
+                .stream()
+                .anyMatch(user -> user.getName().equals(userName));
+    }
+}

service/src/main/java/com/telephoners/krakyournet/ctf/resources/RegistrationResource.java

@@ -2,7 +2,10 @@ package com.telephoners.krakyournet.ctf.resources;
 
 import com.telephoners.krakyournet.ctf.beans.Team;
 import com.telephoners.krakyournet.ctf.beans.User;
+import com.telephoners.krakyournet.ctf.exceptions.ElementAlreadyExistsException;
+import com.telephoners.krakyournet.ctf.exceptions.ElementDoesNotExistException;
 import com.telephoners.krakyournet.ctf.repositories.Repository;
+import com.telephoners.krakyournet.ctf.repositories.UserRepository;
 
 import javax.inject.Inject;
 import javax.inject.Singleton;
@@ -18,10 +21,10 @@ import javax.ws.rs.core.MediaType;
 public class RegistrationResource
 {
     private final Repository<Team> teamsRepository;
-    private final Repository<User> userRepository;
+    private final UserRepository userRepository;
 
     @Inject
-    public RegistrationResource(final Repository<User> userRepository,
+    public RegistrationResource(final UserRepository userRepository,
                                 final Repository<Team> teamsRepository)
     {
         //todo: checkNotNUll
@@ -47,11 +50,8 @@ public class RegistrationResource
     public String register(@QueryParam("userName") final String userName,
                            @QueryParam("teamId") final String teamId)
     {
-        //todo: check if exists
-        if (!teamsRepository.contains(teamId))
-        {
-            throw new RuntimeException("Team does not exist");
-        }
+        validateTeam(teamId);
+        validateUserName(userName);
 
         User user = new User();
         user.setEmail("gpietrusza@gmail.com");
@@ -63,4 +63,14 @@ public class RegistrationResource
 
         return user.getId();
     }
+
+    private void validateTeam(final String teamId)
+    {
+        if(teamsRepository.contains(teamId)) throw new ElementDoesNotExistException(Team.class);
+    }
+
+    private void validateUserName(final String userName)
+    {
+        if(userRepository.exists(userName)) throw new ElementAlreadyExistsException(User.class);
+    }
 }