diff --git a/src/main/java/hhn/labsw/bugageocaching/controller/Controller.java b/src/main/java/hhn/labsw/bugageocaching/controller/Controller.java
index be59059..f4f83a6 100644
--- a/src/main/java/hhn/labsw/bugageocaching/controller/Controller.java
+++ b/src/main/java/hhn/labsw/bugageocaching/controller/Controller.java
@@ -2,6 +2,7 @@ package hhn.labsw.bugageocaching.controller;
 
 import com.google.gson.Gson;
 import hhn.labsw.bugageocaching.entities.*;
+import hhn.labsw.bugageocaching.exceptions.IllegalParameterException;
 import hhn.labsw.bugageocaching.repositories.*;
 import hhn.labsw.bugageocaching.service.SecurityService;
 import hhn.labsw.bugageocaching.service.UserService;
@@ -48,34 +49,57 @@ public class Controller {
 
   @RequestMapping("/allCaches")
   @ResponseBody
-  public String getAllCaches(){
+  public String getAllCaches() {
     return new Gson().toJson(cacheRepository.findAll());
   }
 
   @RequestMapping("/startCache")
   public @ResponseBody
-  Bearbeitet startCache(@RequestParam String userID,
-                        @RequestParam String cacheID,
-                        @RequestParam String cacheAccesDefinitionID) {
+  String startCache(@RequestParam(value = "userID", defaultValue = "-1") String userID,
+                    @RequestParam String cacheID) throws IllegalParameterException {
 
-    Optional<User> userOptional = userRepository.findById(Integer.valueOf(userID));
-    User user = userOptional.get();
+    if (!userID.equals("-1")) { // ein angemeldeter user startet den cache(es werden zwei parameter übergeben)
 
-    Optional<Cache> cacheOptional = cacheRepository.findById(Integer.valueOf(cacheID));
-    Cache cache = cacheOptional.get();
+      Bearbeitet bearbeitet = new Bearbeitet();
 
-    Optional<CacheAccesDefinition> cacheAccesDefinitionOptional =
-        cacheAccesDefinitionRepository.findById(Integer.valueOf(cacheAccesDefinitionID));
-    CacheAccesDefinition cacheAccesDefinition = cacheAccesDefinitionOptional.get();
+      Optional<User> userOptional = userRepository.findById(Integer.valueOf(userID));
+      if (userOptional.isPresent()) {
+        User user = userOptional.get();
+        bearbeitet.setUser(user);
+      } else {
+        throw new IllegalParameterException("There is no user with the ID " + userID);
+      }
 
-    Bearbeitet bearbeitet = new Bearbeitet();
-    bearbeitet.setUser(user);
-    bearbeitet.setCache(cache);
-    bearbeitet.setCacheAccesDefinition(cacheAccesDefinition);
+      Optional<Cache> cacheOptional = cacheRepository.findById(Integer.valueOf(cacheID));
+      if (cacheOptional.isPresent()) {
+        Cache cache = cacheOptional.get();
+        bearbeitet.setCache(cache);
+      } else {
+        throw new IllegalParameterException( "There is no cache with the ID " + cacheID);
+      }
 
-    bearbeitetRepository.save(bearbeitet);
+      Optional<CacheAccesDefinition> cacheAccesDefinitionOptional =
+          cacheAccesDefinitionRepository.findById(1); // bearbeitet
+      if (cacheAccesDefinitionOptional.isPresent()) {
+        CacheAccesDefinition cacheAccesDefinition = cacheAccesDefinitionOptional.get();
+        bearbeitet.setCacheAccesDefinition(cacheAccesDefinition);
+      } else {
+        throw new IllegalParameterException("There is no cacheAccesDefinition with the ID " + 1);
+      }
 
-    return bearbeitet;
+      bearbeitetRepository.save(bearbeitet);
+
+      return new Gson().toJson(bearbeitet);
+
+    } else { // kein angemeldeter User startet den cache(es wird nur der cache als parameter übergeben)
+      Optional<Cache> cacheOptional = cacheRepository.findById(Integer.valueOf(cacheID));
+      if (cacheOptional.isPresent()) {
+        Cache cache = cacheOptional.get();
+        return new Gson().toJson(cache);
+      } else {
+        throw new IllegalParameterException( "There is no cache with the ID " + cacheID);
+      }
+    }
   }
 
   @RequestMapping("/securityCheck")
diff --git a/src/main/java/hhn/labsw/bugageocaching/exceptions/IllegalParameterException.java b/src/main/java/hhn/labsw/bugageocaching/exceptions/IllegalParameterException.java
new file mode 100644
index 0000000..df77bae
--- /dev/null
+++ b/src/main/java/hhn/labsw/bugageocaching/exceptions/IllegalParameterException.java
@@ -0,0 +1,65 @@
+package hhn.labsw.bugageocaching.exceptions;
+
+
+/**
+ * Thrown to indicate that a method has been passed an illegal or inappropriate argument.
+ * This matches the IllegalArgumentException, but is no RuntimeException. This forces the
+ * developer to catch it.
+ * <p>
+ */
+public class IllegalParameterException extends Exception {
+  /**
+   * Constructs a new exception with {@code null} as its detail message.
+   * The cause is not initialized, and may subsequently be initialized by a
+   * call to {@link #initCause}.
+   */
+  public IllegalParameterException() {
+  }
+
+  /**
+   * Constructs a new exception with the specified detail message.  The
+   * cause is not initialized, and may subsequently be initialized by
+   * a call to {@link #initCause}.
+   *
+   * @param message the detail message. The detail message is saved for
+   *                later retrieval by the {@link #getMessage()} method.
+   */
+  public IllegalParameterException(final String message) {
+    super(message);
+  }
+
+  /**
+   * Constructs a new exception with the specified detail message and
+   * cause.  <p>Note that the detail message associated with
+   * {@code cause} is <i>not</i> automatically incorporated in
+   * this exception's detail message.
+   *
+   * @param message the detail message (which is saved for later retrieval
+   *                by the {@link #getMessage()} method).
+   * @param cause   the cause (which is saved for later retrieval by the
+   *                {@link #getCause()} method).  (A <tt>null</tt> value is
+   *                permitted, and indicates that the cause is nonexistent or
+   *                unknown.)
+   * @since 1.4
+   */
+  public IllegalParameterException(final String message, final Throwable cause) {
+    super(message, cause);
+  }
+
+  /**
+   * Constructs a new exception with the specified cause and a detail
+   * message of <tt>(cause==null ? null : cause.toString())</tt> (which
+   * typically contains the class and detail message of <tt>cause</tt>).
+   * This constructor is useful for exceptions that are little more than
+   * wrappers for other throwables.
+   *
+   * @param cause the cause (which is saved for later retrieval by the
+   *              {@link #getCause()} method).  (A <tt>null</tt> value is
+   *              permitted, and indicates that the cause is nonexistent or
+   *              unknown.)
+   * @since 1.4
+   */
+  public IllegalParameterException(final Throwable cause) {
+    super(cause);
+  }
+}