Changed com/col prefix in the comcolfilter (#684)

* User community or collection handle `com_/col_` instead of v5 prefix `hdl_` because it cannot match handle of the community which should not be exposed.

* Throw error when the dso object is not Community or Collection in the ColComFilter.java.

dspace-oai/src/main/java/org/dspace/xoai/filter/ColComFilter.java

@@ -81,7 +81,19 @@ public boolean isShown(DSpaceItem item) {
     }
 
     private String getSetSpec() {
-        return "hdl_" + dso.getHandle().replace("/", "_");
+        // Set prefix for the community as default value.
+        String handlePrefix;
+        if (dso instanceof Collection) {
+            // Prefix for the Collection.
+            handlePrefix = "col_";
+        } else if (dso instanceof Community) {
+            handlePrefix = "com_";
+        } else {
+            String message = "The DSO object must be of type Community or Collection.";
+            log.error(message);
+            throw new RuntimeException(message);
+        }
+        return handlePrefix + dso.getHandle().replace("/", "_");
     }
 
     private DSpaceObject getDSpaceObject() {