Optimize Map methods in ServletAttributesMap

ServletAttributesMap inherited default implementations of the size
and isEmpty methods from AbstractMap which delegates to the Set returned
by entrySet. ServletAttributesMap's entrySet method made this fairly
expensive, since it would copy the attributes to a List, then use a
Stream to build the Set. To avoid the cost, add implementations of
isEmpty / size that don't need to call entrySet at all.

Additionally, change entrySet to return a Set view that simply lazily
delegates to the underlying servlet request for iteration.

Closes gh-32197

spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,10 +26,13 @@ import java.nio.charset.Charset;
 import java.security.Principal;
 import java.time.Instant;
 import java.util.AbstractMap;
+import java.util.AbstractSet;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.Enumeration;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -55,6 +58,7 @@ import org.springframework.http.converter.GenericHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.server.RequestPath;
 import org.springframework.http.server.ServletServerHttpRequest;
+import org.springframework.lang.NonNull;
 import org.springframework.lang.Nullable;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.LinkedMultiValueMap;
@@ -73,6 +77,7 @@ import org.springframework.web.util.UriBuilder;
  *
  * @author Arjen Poutsma
  * @author Sam Brannen
+ * @author Patrick Strawderman
  * @since 5.2
  */
 class DefaultServerRequest implements ServerRequest {
@@ -433,18 +438,77 @@ class DefaultServerRequest implements ServerRequest {
 
 		@Override
 		public void clear() {
-			List<String> attributeNames = Collections.list(this.servletRequest.getAttributeNames());
-			attributeNames.forEach(this.servletRequest::removeAttribute);
+			this.servletRequest.getAttributeNames().asIterator().forEachRemaining(this.servletRequest::removeAttribute);
 		}
 
 		@Override
 		public Set<Entry<String, Object>> entrySet() {
-			return Collections.list(this.servletRequest.getAttributeNames()).stream()
-					.map(name -> {
-						Object value = this.servletRequest.getAttribute(name);
-						return new SimpleImmutableEntry<>(name, value);
-					})
-					.collect(Collectors.toSet());
+			return new AbstractSet<>() {
+				@Override
+				public Iterator<Entry<String, Object>> iterator() {
+					return new Iterator<>() {
+
+						private final Iterator<String> attributes = ServletAttributesMap.this.servletRequest.getAttributeNames().asIterator();
+
+						@Override
+						public boolean hasNext() {
+							return this.attributes.hasNext();
+						}
+
+						@Override
+						public Entry<String, Object> next() {
+							String attribute = this.attributes.next();
+							Object value = ServletAttributesMap.this.servletRequest.getAttribute(attribute);
+							return new SimpleImmutableEntry<>(attribute, value);
+						}
+					};
+				}
+
+				@Override
+				public boolean isEmpty() {
+					return ServletAttributesMap.this.isEmpty();
+				}
+
+				@Override
+				public int size() {
+					return ServletAttributesMap.this.size();
+				}
+
+				@Override
+				public boolean contains(Object o) {
+					if (!(o instanceof Map.Entry<?,?> entry)) {
+						return false;
+					}
+					String attribute = (String) entry.getKey();
+					Object value = ServletAttributesMap.this.servletRequest.getAttribute(attribute);
+					return value != null && value.equals(entry.getValue());
+				}
+
+				@Override
+				public boolean addAll(@NonNull Collection<? extends Entry<String, Object>> c) {
+					throw new UnsupportedOperationException();
+				}
+
+				@Override
+				public boolean remove(Object o) {
+					throw new UnsupportedOperationException();
+				}
+
+				@Override
+				public boolean removeAll(Collection<?> c) {
+					throw new UnsupportedOperationException();
+				}
+
+				@Override
+				public boolean retainAll(@NonNull Collection<?> c) {
+					throw new UnsupportedOperationException();
+				}
+
+				@Override
+				public void clear() {
+					throw new UnsupportedOperationException();
+				}
+			};
 		}
 
 		@Override
@@ -467,6 +531,22 @@ class DefaultServerRequest implements ServerRequest {
 			this.servletRequest.removeAttribute(name);
 			return value;
 		}
+
+		@Override
+		public int size() {
+			Enumeration<String> attributes = this.servletRequest.getAttributeNames();
+			int size = 0;
+			while (attributes.hasMoreElements()) {
+				size++;
+				attributes.nextElement();
+			}
+			return size;
+		}
+
+		@Override
+		public boolean isEmpty() {
+			return !this.servletRequest.getAttributeNames().hasMoreElements();
+		}
 	}
 
 

spring-webmvc/src/test/java/org/springframework/web/servlet/function/DefaultServerRequestTests.java

@@ -27,10 +27,12 @@ import java.security.Principal;
 import java.time.Instant;
 import java.time.temporal.ChronoUnit;
 import java.util.Collections;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.OptionalLong;
+import java.util.Set;
 
 import jakarta.servlet.http.Cookie;
 import jakarta.servlet.http.Part;
@@ -61,8 +63,8 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 
 /**
+ * Tests for {@link DefaultServerRequest}.
  * @author Arjen Poutsma
- * @since 5.1
  */
 class DefaultServerRequestTests {
 
@@ -114,6 +116,46 @@ class DefaultServerRequestTests {
 		assertThat(request.attribute("foo")).contains("bar");
 	}
 
+	@Test
+	void attributes() {
+		MockHttpServletRequest servletRequest = PathPatternsTestUtils.initRequest("GET", "/", true);
+		servletRequest.setAttribute("foo", "bar");
+		servletRequest.setAttribute("baz", "qux");
+
+		DefaultServerRequest request = new DefaultServerRequest(servletRequest, this.messageConverters);
+
+		Map<String, Object> attributesMap = request.attributes();
+		assertThat(attributesMap).isNotEmpty();
+		assertThat(attributesMap).containsEntry("foo", "bar");
+		assertThat(attributesMap).containsEntry("baz", "qux");
+		assertThat(attributesMap).doesNotContainEntry("foo", "blah");
+
+		Set<Map.Entry<String, Object>> entrySet = attributesMap.entrySet();
+		assertThat(entrySet).isNotEmpty();
+		assertThat(entrySet).hasSize(attributesMap.size());
+		assertThat(entrySet).contains(Map.entry("foo", "bar"));
+		assertThat(entrySet).contains(Map.entry("baz", "qux"));
+		assertThat(entrySet).doesNotContain(Map.entry("foo", "blah"));
+		assertThat(entrySet).isUnmodifiable();
+
+		assertThat(entrySet.iterator()).toIterable().contains(Map.entry("foo", "bar"), Map.entry("baz", "qux"));
+		Iterator<String> attributes = servletRequest.getAttributeNames().asIterator();
+		Iterator<Map.Entry<String, Object>> entrySetIterator = entrySet.iterator();
+		while (attributes.hasNext()) {
+			attributes.next();
+			assertThat(entrySetIterator).hasNext();
+			entrySetIterator.next();
+		}
+		assertThat(entrySetIterator).isExhausted();
+
+		attributesMap.clear();
+		assertThat(attributesMap).isEmpty();
+		assertThat(attributesMap).hasSize(0);
+		assertThat(entrySet).isEmpty();
+		assertThat(entrySet).hasSize(0);
+		assertThat(entrySet.iterator()).isExhausted();
+	}
+
 	@Test
 	void params() {
 		MockHttpServletRequest servletRequest = PathPatternsTestUtils.initRequest("GET", "/", true);