diff --git a/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/Utilities.java b/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/Utilities.java
index 89e711590..0d16a1a51 100644
--- a/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/Utilities.java
+++ b/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/Utilities.java
@@ -1286,7 +1286,34 @@ public class Utilities {
     Collections.sort(list);
     return list;
   }
+  
+  public static List<String> sorted(String[] set) {
+    List<String> list = new ArrayList<>();
+    for (String s : set) {
+      list.add(s);
+    }
+    Collections.sort(list);
+    return list;
+  }
 
+
+  public static List<String> reverseSorted(Collection<String> set) {
+    List<String> list = new ArrayList<>();
+    list.addAll(set);
+    Collections.sort(list, Collections.reverseOrder());
+    return list;
+  }
+
+  public static List<String> reverseSorted(String[] set) {
+    List<String> list = new ArrayList<>();
+    for (String s : set) {
+      list.add(s);
+    }
+    Collections.sort(list, Collections.reverseOrder());
+    return list;
+  }
+
+  
   public static void analyseStringDiffs(Set<String> source, Set<String> target, Set<String> missed, Set<String> extra) {
     for (String s : source)
       if (!target.contains(s))
diff --git a/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/npm/FilesystemPackageCacheManager.java b/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/npm/FilesystemPackageCacheManager.java
index 92e086c8c..bd1a194d2 100644
--- a/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/npm/FilesystemPackageCacheManager.java
+++ b/org.hl7.fhir.utilities/src/main/java/org/hl7/fhir/utilities/npm/FilesystemPackageCacheManager.java
@@ -90,8 +90,7 @@ public class FilesystemPackageCacheManager extends BasePackageCacheManager imple
 
 
   public enum FilesystemPackageCacheMode {
-    USER, SYSTEM, TESTING
-
+    USER, SYSTEM, TESTING, CUSTOM
   }
 
   // When running in testing mode, some packages are provided from the test case repository rather than by the normal means
@@ -116,6 +115,7 @@ public class FilesystemPackageCacheManager extends BasePackageCacheManager imple
   private Map<String, String> ciList = new HashMap<String, String>();
   private JsonArray buildInfo;
   private boolean suppressErrors;
+  private boolean minimalMemory;
  
   
   public FilesystemPackageCacheManager(boolean userMode) throws IOException {
@@ -126,6 +126,18 @@ public class FilesystemPackageCacheManager extends BasePackageCacheManager imple
     init(mode);
   }
   
+  /**
+   * Defined for use on Android
+   * 
+   * @param customFolder
+   * @throws IOException
+   */
+  public FilesystemPackageCacheManager(String customFolder) throws IOException {
+    this.cacheFolder = customFolder;
+    init(FilesystemPackageCacheMode.CUSTOM);  
+  }
+  
+  
   public void init(FilesystemPackageCacheMode mode) throws IOException {
     myPackageServers.addAll(PackageServer.publicServers());
 
@@ -139,6 +151,10 @@ public class FilesystemPackageCacheManager extends BasePackageCacheManager imple
     case TESTING:
       cacheFolder = Utilities.path("[tmp]", ".fhir", "packages");
       break;
+    case CUSTOM:
+      if (!new File(cacheFolder).exists()) {
+        throw new FHIRException("The folder ''"+cacheFolder+"' could not be found");
+      }
     default:
       break;    
     }
@@ -150,7 +166,22 @@ public class FilesystemPackageCacheManager extends BasePackageCacheManager imple
     createIniFile();
   }
 
+  public boolean isMinimalMemory() {
+    return minimalMemory;
+  }
+
+  public void setMinimalMemory(boolean minimalMemory) {
+    this.minimalMemory = minimalMemory;
+  }
+
+  /**
+   * do not use this in minimal memory mode
+   * @param packagesFolder
+   * @throws IOException
+   */
   public void loadFromFolder(String packagesFolder) throws IOException {
+    assert !minimalMemory;
+    
     File[] files = new File(packagesFolder).listFiles();
     if (files != null) {
       for (File f : files) {
@@ -165,19 +196,6 @@ public class FilesystemPackageCacheManager extends BasePackageCacheManager imple
     return cacheFolder;
   }
 
-  private List<String> sorted(String[] keys) {
-    List<String> names = new ArrayList<String>();
-    for (String s : keys)
-      names.add(s);
-    Collections.sort(names);
-    return names;
-  }
-
-  private List<String> reverseSorted(String[] keys) {
-    Arrays.sort(keys, Collections.reverseOrder());
-    return Arrays.asList(keys);
-  }
-
   private NpmPackage loadPackageInfo(String path) throws IOException {
     NpmPackage pi = NpmPackage.fromFolder(path);
     return pi;
@@ -284,7 +302,7 @@ public class FilesystemPackageCacheManager extends BasePackageCacheManager imple
   }
 
   public String getLatestVersionFromCache(String id) throws IOException {
-    for (String f : reverseSorted(new File(cacheFolder).list())) {
+    for (String f : Utilities.reverseSorted(new File(cacheFolder).list())) {
       File cf = new File(Utilities.path(cacheFolder, f));
       if (cf.isDirectory()) {
         if (f.startsWith(id + "#")) {
@@ -372,7 +390,7 @@ public class FilesystemPackageCacheManager extends BasePackageCacheManager imple
     }
     String foundPackage = null;
     String foundVersion = null;
-    for (String f : reverseSorted(new File(cacheFolder).list())) {
+    for (String f : Utilities.reverseSorted(new File(cacheFolder).list())) {
       File cf = new File(Utilities.path(cacheFolder, f));
       if (cf.isDirectory()) {
         if (f.equals(id + "#" + version) || (Utilities.noString(version) && f.startsWith(id + "#"))) {
@@ -1017,7 +1035,7 @@ public class FilesystemPackageCacheManager extends BasePackageCacheManager imple
       }
     }
 
-    for (String f : sorted(new File(cacheFolder).list())) {
+    for (String f : Utilities.sorted(new File(cacheFolder).list())) {
       if (f.equals(id + "#" + version) || (Utilities.noString(version) && f.startsWith(id + "#"))) {
         return true;
       }