inject message digest

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

 package com.telephoners.krakyournet.ctf.repositories;
 
+import com.google.inject.name.Named;
 import com.telephoners.krakyournet.ctf.beans.Flag;
 import com.telephoners.krakyournet.ctf.beans.Solution;
 import com.telephoners.krakyournet.ctf.beans.Team;
@@ -14,7 +15,6 @@ import org.mongodb.morphia.Datastore;
 import javax.inject.Inject;
 import javax.inject.Singleton;
 import java.security.MessageDigest;
-import java.security.NoSuchAlgorithmException;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -27,16 +27,19 @@ public class TasksRepository extends Repository<Task>
     private Datastore datastore;
     private TeamsRepository teamsRepository;
     private SolutionsRepository solutionsRepository;
+    private MessageDigest messageDigest;
 
     @Inject
     public TasksRepository(ApplicationConfiguration applicationConfiguration, Datastore datastore,
-                           TeamsRepository teamsRepository, SolutionsRepository solutionsRepository)
+                           TeamsRepository teamsRepository, SolutionsRepository solutionsRepository,
+                           final @Named("messageDigest") MessageDigest messageDigest)
     {
         super(datastore);
         this.applicationConfiguration = applicationConfiguration;
         this.datastore = datastore;
         this.teamsRepository = teamsRepository;
         this.solutionsRepository = solutionsRepository;
+        this.messageDigest = messageDigest;
     }
 
     public Task getByLevel(int level)
@@ -82,16 +85,9 @@ public class TasksRepository extends Repository<Task>
     }
 
     public String calculateHashValue(String username, String flagValue)
-    { //todo
-        String combinedStrings = applicationConfiguration.getSalt() + username + flagValue; //todo
-        MessageDigest md5 = null;//todo: discuss
-        try {
-            md5 = MessageDigest.getInstance(applicationConfiguration.getFlagHashMethod());
-        } catch (NoSuchAlgorithmException e) {
-            e.printStackTrace();
-        }
-        String encodedHash = Hex.encodeHexString(md5.digest(combinedStrings.getBytes()));
-        return encodedHash;
+    {
+        String combinedStrings = applicationConfiguration.getSalt() + username + flagValue;
+        return Hex.encodeHexString(messageDigest.digest(combinedStrings.getBytes()));
     }
 
     private boolean isAlreadySubmittedSolution(Solution solution)