java-21-openjdk/reproducible-properties.patch

--- a/src/java.base/share/classes/java/util/Properties.java
+++ b/src/java.base/share/classes/java/util/Properties.java
@@ -955,7 +955,7 @@ public class Properties extends Hashtable<Object,Object> {
         if (sysPropVal != null && !sysPropVal.isEmpty()) {
             writeComments(bw, sysPropVal);
         } else {
-            bw.write("#" + new Date());
+            bw.write("#" + (System.getenv("SOURCE_DATE_EPOCH") != null ? new Date(1000 * Long.parseLong(System.getenv("SOURCE_DATE_EPOCH"))) : new Date()));
             bw.newLine();
         }
     }