Ensure ClassPathResources with same path and ClassLoader are equal

Prior to this commit, if two ClassPathResource instances were
constructed differently (one from an absolute path and one from a path
relative to a Class) but had the same absolute path and the same
ClassLoader, they were effectively equal, but ClassPathResource#equals
returned false.

This commit addresses this by revising the logic in
ClassPathResource#equals accordingly.

Closes gh-29263

spring-core/src/main/java/org/springframework/core/io/ClassPathResource.java

@@ -24,7 +24,6 @@ import java.net.URL;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
-import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -271,9 +270,14 @@ public class ClassPathResource extends AbstractFileResolvingResource {
 		if (!(other instanceof ClassPathResource otherRes)) {
 			return false;
 		}
-		return (this.path.equals(otherRes.path) &&
-				ObjectUtils.nullSafeEquals(this.classLoader, otherRes.classLoader) &&
-				ObjectUtils.nullSafeEquals(this.clazz, otherRes.clazz));
+		if (!this.absolutePath.equals(otherRes.absolutePath)) {
+			return false;
+		}
+		ClassLoader thisClassLoader =
+				(this.classLoader != null ? this.classLoader : this.clazz.getClassLoader());
+		ClassLoader otherClassLoader =
+				(otherRes.classLoader != null ? otherRes.classLoader : otherRes.clazz.getClassLoader());
+		return thisClassLoader.equals(otherClassLoader);
 	}
 
 	/**

spring-core/src/test/java/org/springframework/core/io/ClassPathResourceTests.java

@@ -30,6 +30,8 @@ import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
+import org.springframework.core.OverridingClassLoader;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.junit.jupiter.api.io.CleanupMode.NEVER;
@@ -79,6 +81,29 @@ class ClassPathResourceTests {
 			assertThat(resource2).isEqualTo(resource1);
 		}
 
+		@Test
+		void resourcesWithEquivalentAbsolutePathsFromTheSameClassLoaderAreEqual() {
+			Resource resource1 = new ClassPathResource("Resource.class", getClass());
+			Resource resource2 = new ClassPathResource("org/springframework/core/io/Resource.class", getClass().getClassLoader());
+			assertThat(resource1).isEqualTo(resource2);
+			assertThat(resource2).isEqualTo(resource1);
+		}
+
+		@Test
+		void resourcesWithEquivalentAbsolutePathsFromDifferentClassLoadersAreNotEqual() {
+			class SimpleThrowawayClassLoader extends OverridingClassLoader {
+				SimpleThrowawayClassLoader(ClassLoader parent) {
+					super(parent);
+				}
+			}
+
+			Resource resource1 = new ClassPathResource("Resource.class", getClass());
+			Resource resource2 = new ClassPathResource("org/springframework/core/io/Resource.class",
+					new SimpleThrowawayClassLoader(getClass().getClassLoader()));
+			assertThat(resource1).isNotEqualTo(resource2);
+			assertThat(resource2).isNotEqualTo(resource1);
+		}
+
 		@Test
 		void relativeResourcesAreEqual() throws Exception {
 			Resource resource = new ClassPathResource("dir/");