# UNDF: UNDF-2026-000000736
--- a/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/EncodedResourceResolver.java
+++ b/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/EncodedResourceResolver.java
@@ -24,6 +24,7 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.LinkedHashSet;
 import java.util.Map;

 import jakarta.servlet.http.HttpServletRequest;
@@ -66,7 +67,8 @@ public class EncodedResourceResolver extends AbstractResourceResolver {

-	private final List<String> contentCodings = new ArrayList<>(DEFAULT_CODINGS);
+	// FIX: Use LinkedHashSet so that contentCodings.contains() is O(1) per
+	// accepted-encoding token on every static-resource request, not O(C).
+	private final LinkedHashSet<String> contentCodings = new LinkedHashSet<>(DEFAULT_CODINGS);


 	public void setContentCodings(List<String> codings) {
 		this.contentCodings.clear();
 		this.contentCodings.addAll(codings);
 	}

 	public List<String> getContentCodings() {
-		return Collections.unmodifiableList(this.contentCodings);
+		return Collections.unmodifiableList(new ArrayList<>(this.contentCodings));
 	}

--- a/spring-webflux/src/main/java/org/springframework/web/reactive/resource/EncodedResourceResolver.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/resource/EncodedResourceResolver.java
@@ -24,6 +24,7 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.LinkedHashSet;
 import java.util.Map;

@@ -67,7 +68,8 @@ public class EncodedResourceResolver extends AbstractResourceResolver {

-	private final List<String> contentCodings = new ArrayList<>(DEFAULT_CODINGS);
+	// FIX: LinkedHashSet for O(1) contains() on per-request accept-encoding scan.
+	private final LinkedHashSet<String> contentCodings = new LinkedHashSet<>(DEFAULT_CODINGS);


 	public void setContentCodings(List<String> codings) {
 		this.contentCodings.clear();
 		this.contentCodings.addAll(codings);
 	}

 	public List<String> getContentCodings() {
-		return Collections.unmodifiableList(this.contentCodings);
+		return Collections.unmodifiableList(new ArrayList<>(this.contentCodings));
 	}