Use an exception to indicate validation errors

src/main/java/org/eclipse/uprotocol/transport/builder/UMessageBuilder.java

@@ -13,6 +13,7 @@
 package org.eclipse.uprotocol.transport.builder;
 
 import org.eclipse.uprotocol.v1.UUri;
+import org.eclipse.uprotocol.validation.ValidationException;
 import org.eclipse.uprotocol.v1.UMessage;
 import org.eclipse.uprotocol.v1.UAttributes;
 import org.eclipse.uprotocol.v1.UCode;
@@ -139,8 +140,10 @@ public static UMessageBuilder response(UUri source, UUri sink, UUID reqid) {
             throw new IllegalArgumentException("sink must be a response and source must be an rpc method.");
         }
 
-        if (UuidValidator.Validators.UPROTOCOL.validator().validate(reqid).getCode() != UCode.OK) {
-            throw new IllegalArgumentException("reqid is not a valid UUID.");
+        try {
+            UuidValidator.Validators.UPROTOCOL.validator().validate(reqid);
+        } catch (ValidationException e) {
+            throw new IllegalArgumentException("reqid is not a valid UUID.", e);
         }
 
         return new UMessageBuilder(source, UuidFactory.Factories.UPROTOCOL.factory().create(),
@@ -159,8 +162,10 @@ public static UMessageBuilder response(UAttributes request) {
         Objects.requireNonNull(request, "request cannot be null.");
 
         // Validate the request
-        if (UAttributesValidator.Validators.REQUEST.validator().validate(request).isFailure()) {
-            throw new IllegalArgumentException("request must contain valid request attributes.");
+        try {
+            UAttributesValidator.Validators.REQUEST.validator().validate(request);
+        } catch (ValidationException e) {
+            throw new IllegalArgumentException("request is not a valid request attributes.", e);
         }
 
         return new UMessageBuilder(

src/main/java/org/eclipse/uprotocol/uuid/validate/UuidValidator.java

@@ -14,13 +14,11 @@
 
 import org.eclipse.uprotocol.uuid.factory.UuidUtils;
 import org.eclipse.uprotocol.v1.UUID;
-import org.eclipse.uprotocol.v1.UStatus;
-import org.eclipse.uprotocol.v1.UCode;
-import org.eclipse.uprotocol.validation.ValidationResult;
+import org.eclipse.uprotocol.validation.ValidationException;
+import org.eclipse.uprotocol.validation.ValidationUtils;
 
+import java.util.Objects;
 import java.util.Optional;
-import java.util.stream.Collectors;
-import java.util.stream.Stream;
 
 /**
  * A Validator for uProtocol UUIDs.
@@ -53,48 +51,63 @@ public UuidValidator validator() {
         }
     }
 
-    public UStatus validate(UUID uuid) {
-        final String errorMessage = Stream.of(
-                validateVersion(uuid),
-                validateTime(uuid))
-                .filter(ValidationResult::isFailure)
-            .map(ValidationResult::getMessage)
-            .collect(Collectors.joining(","));
-        return errorMessage.isBlank() ? ValidationResult.success().toStatus()
-                : UStatus.newBuilder().setCode(UCode.INVALID_ARGUMENT).setMessage(errorMessage).build();
+    /**
+     * Checks if a UUID is valid according to the specific variant/version of the UUID.
+     *
+     * @param uuid The UUID to validate.
+     * @throws NullPointerException if the UUID is null.
+     * @throws ValidationException if the UUID is invalid.
+     */
+    public void validate(UUID uuid) {
+        Objects.requireNonNull(uuid);
+        final var errors = ValidationUtils.collectErrors(uuid,
+            this::validateVersion,
+            this::validateTime
+        );
+        if (!errors.isEmpty()) {
+            throw new ValidationException(errors);
+        }
     }
 
-    public abstract ValidationResult validateVersion(UUID uuid);
+    /**
+     * Validates the version of the UUID.
+     *
+     * @param uuid The UUID to check.
+     * @throws ValidationException if the UUID is invalid.
+     */
+    public abstract void validateVersion(UUID uuid);
 
-    public ValidationResult validateTime(UUID uuid) {
+    public void validateTime(UUID uuid) {
         final Optional<Long> time = UuidUtils.getTime(uuid);
-        return time.isPresent() && (time.get() > 0) ? ValidationResult.success()
-                : ValidationResult.failure(String.format("Invalid UUID Time"));
+        if (time.isPresent() && (time.get() > 0)) {
+            return;
+        }
+        throw new ValidationException("Invalid UUID Time");
     }
 
     private static class InvalidValidator extends UuidValidator {
 
         @Override
-        public ValidationResult validateVersion(UUID uuid) {
-            return ValidationResult.failure(String.format("Invalid UUID Version"));
+        public void validateVersion(UUID uuid) {
+            throw new ValidationException("Invalid UUID Version");
         }
     }
 
     private static class UUIDv6Validator extends UuidValidator {
         @Override
-        public ValidationResult validateVersion(UUID uuid) {
-            return UuidUtils.isUuidv6(uuid)
-                    ? ValidationResult.success()
-                    : ValidationResult.failure(String.format("Not a UUIDv6 Version"));
+        public void validateVersion(UUID uuid) {
+            if (!UuidUtils.isUuidv6(uuid)) {
+                throw new ValidationException("Not a UUIDv6 Version");
+            }
         }
     }
 
     private static class UUIDv7Validator extends UuidValidator {
         @Override
-        public ValidationResult validateVersion(UUID uuid) {
-            return UuidUtils.isUProtocol(uuid)
-                    ? ValidationResult.success()
-                    : ValidationResult.failure(String.format("Invalid UUIDv7 Version"));
+        public void validateVersion(UUID uuid) {
+            if (!UuidUtils.isUProtocol(uuid)) {
+                throw new ValidationException("Invalid UUIDv7 Version");
+            }
         }
     }
 }

src/main/java/org/eclipse/uprotocol/validation/ValidationException.java

@@ -0,0 +1,64 @@
+/**
+ * SPDX-FileCopyrightText: 2025 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+package org.eclipse.uprotocol.validation;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Indicates an error that has occurred during validation of a uProtocol type.
+ */
+public class ValidationException extends RuntimeException {
+
+    private static final long serialVersionUID = 1L;
+    private final List<Exception> causes;
+
+    /**
+     * Creates a new exception for an error message.
+     *
+     * @param message The message.
+     */
+    public ValidationException(String message) {
+        super(message);
+        this.causes = List.of();
+    }
+
+    /**
+     * Creates a new exception for multiple causes.
+     *
+     * @param causes The causes for the validation failure.
+     */
+    public ValidationException(List<Exception> causes) {
+        super("Multiple validation errors");
+        this.causes = List.copyOf(causes);
+    }
+
+    @Override
+    public String getMessage() {
+        if (causes.isEmpty()) {
+            return super.getMessage();
+        }
+        return causes.stream()
+            .map(Exception::getMessage)
+            .collect(Collectors.joining(","));
+    }
+
+    /**
+     * Gets the causes of this exception.
+     *
+     * @return An unmodifiable view of the causes.
+     */
+    public final List<Exception> getCauses() {
+        return causes;
+    }
+}

src/main/java/org/eclipse/uprotocol/validation/ValidationUtils.java

@@ -0,0 +1,52 @@
+/**
+ * SPDX-FileCopyrightText: 2024 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+package org.eclipse.uprotocol.validation;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+import java.util.function.Consumer;
+import java.util.stream.Collectors;
+
+public final class ValidationUtils {
+
+    private ValidationUtils() {
+        // Utility class
+    }
+
+    /**
+     * Collects all exception thrown by checks performed on a given subject.
+     *
+     * @param <T> The type of the subject.
+     * @param subject The subject to perform checks on.
+     * @param checks The validation checks to perform.
+     * @return A list of exceptions thrown during validation.
+     */
+    @SafeVarargs
+    public static <T> List<Exception> collectErrors(T subject, Consumer<T>... checks) {
+        Objects.requireNonNull(subject);
+        Objects.requireNonNull(checks);
+
+        return Arrays.stream(checks)
+            .map(check -> {
+                try {
+                    check.accept(subject);
+                    return null; // No exception = valid
+                } catch (Exception e) {
+                    return e;
+                }
+            })
+            .filter(Objects::nonNull)
+            .collect(Collectors.toList());
+    }
+}

src/test/java/org/eclipse/uprotocol/communication/TestUTransport.java

@@ -32,7 +32,7 @@
 import org.eclipse.uprotocol.v1.UMessageType;
 import org.eclipse.uprotocol.v1.UStatus;
 import org.eclipse.uprotocol.v1.UUri;
-import org.eclipse.uprotocol.validation.ValidationResult;
+import org.eclipse.uprotocol.validation.ValidationException;
 
 import com.google.protobuf.InvalidProtocolBufferException;
 
@@ -85,9 +85,16 @@ public TestUTransport(UUri source) {
 
     @Override
     public CompletionStage<UStatus> send(UMessage message) {
+        if (message == null) {
+            return CompletableFuture.completedFuture(UStatus.newBuilder()
+                .setCode(UCode.INVALID_ARGUMENT)
+                .setMessage("Message cannot be null")
+                .build());
+        }
         UAttributesValidator validator = UAttributesValidator.getValidator(message.getAttributes());
-
-        if ( (message == null) || validator.validate(message.getAttributes()) != ValidationResult.success()) {
+        try {
+            validator.validate(message.getAttributes());
+        } catch (ValidationException e) {
             return CompletableFuture.completedFuture(UStatus.newBuilder()
                 .setCode(UCode.INVALID_ARGUMENT)
                 .setMessage("Invalid message attributes")