Polish "Wrap 'error' attribute for consistent JSON serialization"

Polish code and extend wrapping to all error types.

See gh-43330

Author: philwebb

Diff for: spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/error/Error.java

@@ -0,0 +1,109 @@
+/*
+ * Copyright 2012-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.web.error;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+
+import org.springframework.context.MessageSourceResolvable;
+import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
+
+/**
+ * A wrapper class for {@link MessageSourceResolvable} errors that is safe for JSON
+ * serialization.
+ *
+ * @author Yongjun Hong
+ * @author Phillip Webb
+ * @since 3.5.0
+ */
+public final class Error implements MessageSourceResolvable {
+
+	private final MessageSourceResolvable cause;
+
+	/**
+	 * Create a new {@code Error} instance with the specified cause.
+	 * @param cause the error cause (must not be {@code null})
+	 */
+	private Error(MessageSourceResolvable cause) {
+		Assert.notNull(cause, "'cause' must not be null");
+		this.cause = cause;
+	}
+
+	@Override
+	public String[] getCodes() {
+		return this.cause.getCodes();
+	}
+
+	@Override
+	public Object[] getArguments() {
+		return this.cause.getArguments();
+	}
+
+	@Override
+	public String getDefaultMessage() {
+		return this.cause.getDefaultMessage();
+	}
+
+	/**
+	 * Return the original cause of the error.
+	 * @return the error cause
+	 */
+	public MessageSourceResolvable getCause() {
+		return this.cause;
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj) {
+			return true;
+		}
+		if (obj == null || getClass() != obj.getClass()) {
+			return false;
+		}
+		return Objects.equals(this.cause, ((Error) obj).cause);
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(this.cause);
+	}
+
+	@Override
+	public String toString() {
+		return this.cause.toString();
+	}
+
+	/**
+	 * Wrap the given errors.
+	 * @param errors the errors to wrap
+	 * @return a new Error list
+	 */
+	public static List<Error> wrap(List<? extends MessageSourceResolvable> errors) {
+		if (CollectionUtils.isEmpty(errors)) {
+			return Collections.emptyList();
+		}
+		List<Error> result = new ArrayList<>(errors.size());
+		for (MessageSourceResolvable error : errors) {
+			result.add(new Error(error));
+		}
+		return List.copyOf(result);
+	}
+
+}

Diff for: spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/error/ErrorWrapper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -20,11 +20,10 @@
 import java.io.StringWriter;
 import java.util.Date;
 import java.util.LinkedHashMap;
-import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 
-import org.springframework.boot.web.error.ErrorWrapper;
+import org.springframework.boot.web.error.Error;
 import org.springframework.boot.web.error.ErrorAttributeOptions;
 import org.springframework.boot.web.error.ErrorAttributeOptions.Include;
 import org.springframework.core.annotation.MergedAnnotation;
@@ -48,7 +47,7 @@
  * <li>error - The error reason</li>
  * <li>exception - The class name of the root exception (if configured)</li>
  * <li>message - The exception message (if configured)</li>
- * <li>errors - Any validation errors wrapped in {@link ErrorWrapper}, derived from a
+ * <li>errors - Any validation errors wrapped in {@link Error}, derived from a
  * {@link BindingResult} or {@link MethodValidationResult} exception (if configured)</li>
  * <li>trace - The exception stack trace (if configured)</li>
  * <li>path - The URL path when the exception was raised</li>
@@ -113,19 +112,20 @@ private void handleException(Map<String, Object> errorAttributes, Throwable erro
 			MergedAnnotation<ResponseStatus> responseStatusAnnotation, boolean includeStackTrace) {
 		Throwable exception;
 		if (error instanceof BindingResult bindingResult) {
-			errorAttributes.put("message", error.getMessage());
-			errorAttributes.put("errors", bindingResult.getAllErrors());
 			exception = error;
+			errorAttributes.put("message", error.getMessage());
+			errorAttributes.put("errors", Error.wrap(bindingResult.getAllErrors()));
 		}
 		else if (error instanceof MethodValidationResult methodValidationResult) {
-			addMessageAndErrorsFromMethodValidationResult(errorAttributes, methodValidationResult);
 			exception = error;
+			errorAttributes.put("message", getErrorMessage(methodValidationResult));
+			errorAttributes.put("errors", Error.wrap(methodValidationResult.getAllErrors()));
 		}
 		else if (error instanceof ResponseStatusException responseStatusException) {
-			errorAttributes.put("message", responseStatusException.getReason());
 			exception = (responseStatusException.getCause() != null) ? responseStatusException.getCause() : error;
+			errorAttributes.put("message", responseStatusException.getReason());
 			if (exception instanceof BindingResult bindingResult) {
-				errorAttributes.put("errors", bindingResult.getAllErrors());
+				errorAttributes.put("errors", Error.wrap(bindingResult.getAllErrors()));
 			}
 		}
 		else {
@@ -140,15 +140,9 @@ else if (error instanceof ResponseStatusException responseStatusException) {
 		}
 	}
 
-	private void addMessageAndErrorsFromMethodValidationResult(Map<String, Object> errorAttributes,
-			MethodValidationResult result) {
-		List<ErrorWrapper> errors = result.getAllErrors()
-			.stream()
-			.map(ErrorWrapper::new)
-			.toList();
-		errorAttributes.put("message",
-				"Validation failed for method='" + result.getMethod() + "'. Error count: " + errors.size());
-		errorAttributes.put("errors", errors);
+	private String getErrorMessage(MethodValidationResult methodValidationResult) {
+		return "Validation failed for method='%s'. Error count: %s".formatted(methodValidationResult.getMethod(),
+				methodValidationResult.getAllErrors().size());
 	}
 
 	@Override

Diff for: spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/reactive/error/DefaultErrorAttributes.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -20,24 +20,22 @@
 import java.io.StringWriter;
 import java.util.Date;
 import java.util.LinkedHashMap;
-import java.util.List;
 import java.util.Map;
 
 import jakarta.servlet.RequestDispatcher;
 import jakarta.servlet.ServletException;
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
 
+import org.springframework.boot.web.error.Error;
 import org.springframework.boot.web.error.ErrorAttributeOptions;
 import org.springframework.boot.web.error.ErrorAttributeOptions.Include;
-import org.springframework.boot.web.error.ErrorWrapper;
 import org.springframework.core.Ordered;
 import org.springframework.core.annotation.Order;
 import org.springframework.http.HttpStatus;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.validation.BindingResult;
-import org.springframework.validation.ObjectError;
 import org.springframework.validation.method.MethodValidationResult;
 import org.springframework.web.context.request.RequestAttributes;
 import org.springframework.web.context.request.WebRequest;
@@ -53,7 +51,7 @@
  * <li>error - The error reason</li>
  * <li>exception - The class name of the root exception (if configured)</li>
  * <li>message - The exception message (if configured)</li>
- * <li>errors - Any validation errors wrapped in {@link ErrorWrapper}, derived from a
+ * <li>errors - Any validation errors wrapped in {@link Error}, derived from a
  * {@link BindingResult} or {@link MethodValidationResult} exception (if configured)</li>
  * <li>trace - The exception stack trace (if configured)</li>
  * <li>path - The URL path when the exception was raised</li>
@@ -143,27 +141,27 @@ private void addErrorMessage(Map<String, Object> errorAttributes, WebRequest web
 		BindingResult bindingResult = extractBindingResult(error);
 		if (bindingResult != null) {
 			addMessageAndErrorsFromBindingResult(errorAttributes, bindingResult);
+			return;
 		}
-		else {
-			MethodValidationResult methodValidationResult = extractMethodValidationResult(error);
-			if (methodValidationResult != null) {
-				addMessageAndErrorsFromMethodValidationResult(errorAttributes, methodValidationResult);
-			}
-			else {
-				addExceptionErrorMessage(errorAttributes, webRequest, error);
-			}
+		MethodValidationResult methodValidationResult = extractMethodValidationResult(error);
+		if (methodValidationResult != null) {
+			addMessageAndErrorsFromMethodValidationResult(errorAttributes, methodValidationResult);
+			return;
 		}
+		addExceptionErrorMessage(errorAttributes, webRequest, error);
+	}
+
+	private void addMessageAndErrorsFromBindingResult(Map<String, Object> errorAttributes, BindingResult result) {
+		errorAttributes.put("message", "Validation failed for object='%s'. Error count: %s"
+			.formatted(result.getObjectName(), result.getAllErrors().size()));
+		errorAttributes.put("errors", Error.wrap(result.getAllErrors()));
 	}
 
 	private void addMessageAndErrorsFromMethodValidationResult(Map<String, Object> errorAttributes,
 			MethodValidationResult result) {
-		List<ErrorWrapper> errors = result.getAllErrors()
-			.stream()
-			.map(ErrorWrapper::new)
-			.toList();
-		errorAttributes.put("message",
-				"Validation failed for method='" + result.getMethod() + "'. Error count: " + errors.size());
-		errorAttributes.put("errors", errors);
+		errorAttributes.put("message", "Validation failed for method='%s'. Error count: %s"
+			.formatted(result.getMethod(), result.getAllErrors().size()));
+		errorAttributes.put("errors", Error.wrap(result.getAllErrors()));
 	}
 
 	private void addExceptionErrorMessage(Map<String, Object> errorAttributes, WebRequest webRequest, Throwable error) {
@@ -195,17 +193,6 @@ protected String getMessage(WebRequest webRequest, Throwable error) {
 		return "No message available";
 	}
 
-	private void addMessageAndErrorsFromBindingResult(Map<String, Object> errorAttributes, BindingResult result) {
-		addMessageAndErrorsForValidationFailure(errorAttributes, "object='" + result.getObjectName() + "'",
-				result.getAllErrors());
-	}
-
-	private void addMessageAndErrorsForValidationFailure(Map<String, Object> errorAttributes, String validated,
-			List<ObjectError> errors) {
-		errorAttributes.put("message", "Validation failed for " + validated + ". Error count: " + errors.size());
-		errorAttributes.put("errors", errors);
-	}
-
 	private BindingResult extractBindingResult(Throwable error) {
 		if (error instanceof BindingResult bindingResult) {
 			return bindingResult;