File reproducible-javadoc-timestamp.patch of Package java-21-openjdk.34816

diff --git a/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/HtmlConfiguration.java b/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/HtmlConfiguration.java
index 6bff863e178..60c01d18320 100644
--- a/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/HtmlConfiguration.java
+++ b/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/HtmlConfiguration.java
@@ -25,7 +25,9 @@
 
 package jdk.javadoc.internal.doclets.formats.html;
 
+import java.time.Instant;
 import java.time.ZonedDateTime;
+import java.time.ZoneId;
 import java.util.ArrayList;
 import java.util.EnumSet;
 import java.util.HashMap;
@@ -264,8 +266,12 @@ public class HtmlConfiguration extends BaseConfiguration {
             return false;
         }
 
+        ZonedDateTime now = ZonedDateTime.now();
+        if ( System.getenv("SOURCE_DATE_EPOCH") != null ) {
+            now = ZonedDateTime.ofInstant(Instant.ofEpochMilli(1000 * Long.parseLong(System.getenv("SOURCE_DATE_EPOCH"))), ZoneId.of("UTC"));
+        }
         ZonedDateTime zdt = options.date();
-        buildDate = zdt != null ? zdt : ZonedDateTime.now();
+        buildDate = zdt != null ? zdt : now;
 
         if (!getSpecifiedTypeElements().isEmpty()) {
             Map<String, PackageElement> map = new HashMap<>();