Finalize constants in JavamelodyFilter

Change-Id: I5c3538d7ec917f08c92f32429c1e6c3cc8132ac3
Signed-off-by: Jacek Centkowski <jcentkowski@collab.net>
diff --git a/src/main/java/com/googlesource/gerrit/plugins/javamelody/GerritMonitoringFilter.java b/src/main/java/com/googlesource/gerrit/plugins/javamelody/GerritMonitoringFilter.java
index 4628d8a..c537800 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/javamelody/GerritMonitoringFilter.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/javamelody/GerritMonitoringFilter.java
@@ -75,9 +75,9 @@
   }
 
   static class JavamelodyFilter extends MonitoringFilter {
-    private static String HTTP_TRANSFORM_PATTERN = "http-transform-pattern";
-    private static String GLOBAL_HTTP_TRANSFORM_PATTERN = "javamelody." + HTTP_TRANSFORM_PATTERN;
-    static String GERRIT_GROUPING =
+    private static final String HTTP_TRANSFORM_PATTERN = "http-transform-pattern";
+    private static final String GLOBAL_HTTP_TRANSFORM_PATTERN = "javamelody." + HTTP_TRANSFORM_PATTERN;
+    static final String GERRIT_GROUPING =
         new StringJoiner("|")
             .add("[0-9a-f]{64}") // Long SHA for LFS
             .add("[0-9a-f]{40}") // SHA-1