Fix contract violations in ConcurrentReferenceHashMap's EntrySet/Iterator

Closes gh-27454

(cherry picked from commit 208fafa4a3)

spring-core/src/main/java/org/springframework/util/ConcurrentReferenceHashMap.java

@@ -858,7 +858,7 @@ public class ConcurrentReferenceHashMap<K, V> extends AbstractMap<K, V> implemen
 				Reference<K, V> ref = ConcurrentReferenceHashMap.this.getReference(entry.getKey(), Restructure.NEVER);
 				Entry<K, V> otherEntry = (ref != null ? ref.get() : null);
 				if (otherEntry != null) {
-					return ObjectUtils.nullSafeEquals(otherEntry.getValue(), otherEntry.getValue());
+					return ObjectUtils.nullSafeEquals(entry.getValue(), otherEntry.getValue());
 				}
 			}
 			return false;
@@ -966,6 +966,7 @@ public class ConcurrentReferenceHashMap<K, V> extends AbstractMap<K, V> implemen
 		public void remove() {
 			Assert.state(this.last != null, "No element to remove");
 			ConcurrentReferenceHashMap.this.remove(this.last.getKey());
+			this.last = null;
 		}
 	}
 

spring-core/src/test/java/org/springframework/util/ConcurrentReferenceHashMapTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -41,11 +41,13 @@ import org.springframework.util.comparator.NullSafeComparator;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 
 /**
  * Tests for {@link ConcurrentReferenceHashMap}.
  *
  * @author Phillip Webb
+ * @author Juergen Hoeller
  */
 class ConcurrentReferenceHashMapTests {
 
@@ -466,6 +468,7 @@ class ConcurrentReferenceHashMapTests {
 		iterator.next();
 		iterator.next();
 		iterator.remove();
+		assertThatIllegalStateException().isThrownBy(iterator::remove);
 		iterator.next();
 		assertThat(iterator.hasNext()).isFalse();
 		assertThat(this.map).hasSize(2);
@@ -486,6 +489,26 @@ class ConcurrentReferenceHashMapTests {
 		assertThat(this.map.get(2)).isEqualTo("2b");
 	}
 
+	@Test
+	void containsViaEntrySet() {
+		this.map.put(1, "1");
+		this.map.put(2, "2");
+		this.map.put(3, "3");
+		Set<Map.Entry<Integer, String>> entrySet = this.map.entrySet();
+		Set<Map.Entry<Integer, String>> copy = new HashMap<>(this.map).entrySet();
+		copy.forEach(entry -> assertThat(entrySet.contains(entry)).isTrue());
+		this.map.put(1, "A");
+		this.map.put(2, "B");
+		this.map.put(3, "C");
+		copy.forEach(entry -> assertThat(entrySet.contains(entry)).isFalse());
+		this.map.put(1, "1");
+		this.map.put(2, "2");
+		this.map.put(3, "3");
+		copy.forEach(entry -> assertThat(entrySet.contains(entry)).isTrue());
+		entrySet.clear();
+		copy.forEach(entry -> assertThat(entrySet.contains(entry)).isFalse());
+	}
+
 	@Test
 	@Disabled("Intended for use during development only")
 	void shouldBeFasterThanSynchronizedMap() throws InterruptedException {
@@ -583,7 +606,7 @@ class ConcurrentReferenceHashMapTests {
 			}
 			// For testing we want more control of the hash
 			this.supplementalHash = super.getHash(o);
-			return o == null ? 0 : o.hashCode();
+			return (o != null ? o.hashCode() : 0);
 		}
 
 		public int getSupplementalHash() {