Improve ProblemDetail equals and hashCode

Lazy computed title property should be taken into account

See gh-30294

Author: quaff

spring-web/src/main/java/org/springframework/http/ProblemDetail.java

@@ -42,6 +42,7 @@
  *
  * @author Rossen Stoyanchev
  * @author Juergen Hoeller
+ * @author Yanming Zhou
  * @since 6.0
  * @see <a href="https://datatracker.ietf.org/doc/html/rfc7807">RFC 7807</a>
  * @see org.springframework.web.ErrorResponse
@@ -239,7 +240,7 @@ public boolean equals(@Nullable Object other) {
 			return false;
 		}
 		return (this.type.equals(otherDetail.type) &&
-				ObjectUtils.nullSafeEquals(this.title, otherDetail.title) &&
+				ObjectUtils.nullSafeEquals(this.getTitle(), otherDetail.getTitle()) &&
 				this.status == otherDetail.status &&
 				ObjectUtils.nullSafeEquals(this.detail, otherDetail.detail) &&
 				ObjectUtils.nullSafeEquals(this.instance, otherDetail.instance) &&
@@ -249,7 +250,7 @@ public boolean equals(@Nullable Object other) {
 	@Override
 	public int hashCode() {
 		int result = this.type.hashCode();
-		result = 31 * result + ObjectUtils.nullSafeHashCode(this.title);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(this.getTitle());
 		result = 31 * result + this.status;
 		result = 31 * result + ObjectUtils.nullSafeHashCode(this.detail);
 		result = 31 * result + ObjectUtils.nullSafeHashCode(this.instance);

spring-web/src/test/java/org/springframework/http/ProblemDetailTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.http;
 
+import com.fasterxml.jackson.databind.ObjectMapper;
 import org.junit.jupiter.api.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -24,11 +25,12 @@
  * Unit tests for {@link ProblemDetail}.
  *
  * @author Juergen Hoeller
+ * @author Yanming Zhou
  */
 class ProblemDetailTests {
 
 	@Test
-	void equalsAndHashCode() {
+	void equalsAndHashCode() throws Exception {
 		ProblemDetail pd1 = ProblemDetail.forStatus(500);
 		ProblemDetail pd2 = ProblemDetail.forStatus(HttpStatus.INTERNAL_SERVER_ERROR);
 		ProblemDetail pd3 = ProblemDetail.forStatus(HttpStatus.NOT_FOUND);
@@ -48,6 +50,12 @@ void equalsAndHashCode() {
 		assertThat(pd2).isNotEqualTo(pd4);
 		assertThat(pd1.hashCode()).isNotEqualTo(pd3.hashCode());
 		assertThat(pd1.hashCode()).isNotEqualTo(pd4.hashCode());
+
+		ObjectMapper om = new ObjectMapper();
+		ProblemDetail pd5 = om.readValue(om.writeValueAsBytes(pd1), ProblemDetail.class);
+		assertThat(pd1).isEqualTo(pd5);
+		assertThat(pd5).isEqualTo(pd1);
+		assertThat(pd1.hashCode()).isEqualTo(pd5.hashCode());
 	}
 
 }