When dealing with duplicated zipentries, Zip checks modification times before
overwriting the zipentry. If you specify duplicate="add", zipentries will be
overwriten only if the present zipentry is older than the one you're trying to add.

In some situations it would be nice to override this behaviour and force zip to
overwrite zipentries even if the file you're adding is older than the zipentry
in the zip file.

The following patch should do the trick (please shout if there is a better way
of submitting patch suggestions):

Index: src/main/org/apache/tools/ant/taskdefs/Zip.java

===================================================================

--- src/main/org/apache/tools/ant/taskdefs/Zip.java	(revision 384498)

+++ src/main/org/apache/tools/ant/taskdefs/Zip.java	(working copy)

@@ -1130,11 +1130,15 @@

                 resources = selectFileResources(resources);
             }
 
-            newerResources[i] =
-                ResourceUtils.selectOutOfDateSources(this,
+            if(duplicate.equals("overwrite")){
+                newerResources[i] = resources;
+            } else {
+                newerResources[i] =
+                    ResourceUtils.selectOutOfDateSources(this,
                                                      resources,
                                                      myMapper,
                                                      getZipScanner());
+            }
             needsUpdate = needsUpdate || (newerResources[i].length > 0);
 
             if (needsUpdate && !doUpdate) {
@@ -1647,7 +1651,7 @@

          * @see EnumeratedAttribute#getValues()
          */
         public String[] getValues() {
-            return new String[] {"add", "preserve", "fail"};
+            return new String[] {"add", "preserve", "fail", "overwrite"};
         }
     }