Issue #106: Introduced an HTTP status validator.

This class is meant to be used within instantiation of CommandResponses.

Signed-off-by: Juergen Fickel <juergen.fickel@bosch.io>

base/model/src/main/java/org/eclipse/ditto/base/model/signals/commands/CommandResponseHttpStatusValidator.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2021 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 Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.eclipse.ditto.base.model.signals.commands;
+
+import static org.eclipse.ditto.base.model.common.ConditionChecker.checkNotNull;
+
+import java.text.MessageFormat;
+import java.util.Collection;
+
+import javax.annotation.concurrent.Immutable;
+
+import org.eclipse.ditto.base.model.common.ConditionChecker;
+import org.eclipse.ditto.base.model.common.HttpStatus;
+
+/**
+ * Validates if a particular {@link HttpStatus} is valid for a certain {@link CommandResponse}.
+ *
+ * @since 2.3.0
+ */
+@Immutable
+public final class CommandResponseHttpStatusValidator {
+
+    private CommandResponseHttpStatusValidator() {
+        throw new AssertionError();
+    }
+
+    /**
+     * Checks if the specified {@code HttpStatus} argument is contained in the also specified allowed HTTP statuses
+     * argument.
+     *
+     * @param httpStatus the HTTP status to be validated.
+     * @param allowedHttpStatuses the HTTP statuses that are allowed.
+     * @param commandResponseType is required to build a descriptive error message in case validation failed.
+     * @return {@code httpStatus} if it is valid.
+     * @throws NullPointerException if any argument is {@code null}.
+     * @throws IllegalArgumentException if {@code allowedHttpStatuses} is empty or if {@code httpStatus} is not in
+     * {@code allowedHttpStatuses}.
+     */
+    public static HttpStatus validateHttpStatus(final HttpStatus httpStatus,
+            final Collection<HttpStatus> allowedHttpStatuses,
+            final Class<? extends CommandResponse> commandResponseType) {
+
+        ConditionChecker.argumentNotEmpty(allowedHttpStatuses, "allowedHttpStatuses");
+        checkNotNull(commandResponseType, "commandResponseType");
+        return ConditionChecker.checkArgument(checkNotNull(httpStatus, "httpStatus"),
+                allowedHttpStatuses::contains,
+                () -> MessageFormat.format("{0} is invalid. {1} only allows {2}.",
+                        httpStatus,
+                        commandResponseType.getSimpleName(),
+                        allowedHttpStatuses));
+    }
+
+}

base/model/src/test/java/org/eclipse/ditto/base/model/signals/commands/CommandResponseHttpStatusValidatorTest.java

@@ -0,0 +1,105 @@
+/*
+ * Copyright (c) 2021 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 Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.eclipse.ditto.base.model.signals.commands;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mutabilitydetector.unittesting.MutabilityAssert.assertInstancesOf;
+import static org.mutabilitydetector.unittesting.MutabilityMatchers.areImmutable;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import org.assertj.core.api.Assertions;
+import org.eclipse.ditto.base.model.common.HttpStatus;
+import org.junit.Test;
+
+/**
+ * Unit test for {@link CommandResponseHttpStatusValidator}.
+ */
+public final class CommandResponseHttpStatusValidatorTest {
+
+    @Test
+    public void assertImmutability() {
+        assertInstancesOf(CommandResponseHttpStatusValidator.class, areImmutable());
+    }
+
+    @Test
+    public void validateHttpStatusWithNullHttpStatusThrowsNullPointerException() {
+        Assertions.assertThatNullPointerException()
+                .isThrownBy(() -> CommandResponseHttpStatusValidator.validateHttpStatus(null,
+                        Collections.singleton(HttpStatus.OK),
+                        AbstractCommandResponse.class))
+                .withMessage("The httpStatus must not be null!")
+                .withNoCause();
+    }
+
+    @Test
+    public void validateHttpStatusWithNullAllowedHttpStatusesThrowsNullPointerException() {
+        Assertions.assertThatNullPointerException()
+                .isThrownBy(() -> CommandResponseHttpStatusValidator.validateHttpStatus(HttpStatus.OK,
+                        null,
+                        AbstractCommandResponse.class))
+                .withMessage("The allowedHttpStatuses must not be null!")
+                .withNoCause();
+    }
+
+    @Test
+    public void validateHttpStatusWithEmptyAllowedHttpStatusesThrowsIllegalArgumentException() {
+        Assertions.assertThatIllegalArgumentException()
+                .isThrownBy(() -> CommandResponseHttpStatusValidator.validateHttpStatus(HttpStatus.OK,
+                        Collections.emptySet(),
+                        AbstractCommandResponse.class))
+                .withMessage("The argument 'allowedHttpStatuses' must not be empty!")
+                .withNoCause();
+    }
+
+    @Test
+    public void validateHttpStatusWithNullCommandResponseTypeThrowsNullPointerException() {
+        Assertions.assertThatNullPointerException()
+                .isThrownBy(() -> CommandResponseHttpStatusValidator.validateHttpStatus(HttpStatus.OK,
+                        Collections.singleton(HttpStatus.OK),
+                        null))
+                .withMessage("The commandResponseType must not be null!")
+                .withNoCause();
+    }
+
+    @Test
+    public void validateHttpStatusWithAllowedHttpStatusReturnsExpected() {
+        final HttpStatus httpStatus = HttpStatus.NO_CONTENT;
+
+        final HttpStatus validHttpStatus = CommandResponseHttpStatusValidator.validateHttpStatus(httpStatus,
+                Arrays.asList(HttpStatus.OK, HttpStatus.CREATED, HttpStatus.NO_CONTENT),
+                AbstractCommandResponse.class);
+
+        assertThat(validHttpStatus).isEqualTo(httpStatus);
+    }
+
+    @Test
+    public void validateHttpStatusWithDisallowedHttpStatusThrowsIllegalArgumentException() {
+        final HttpStatus httpStatus = HttpStatus.OK;
+        final List<HttpStatus> allowedHttpStatuses = Arrays.asList(HttpStatus.CREATED, HttpStatus.NO_CONTENT);
+        final Class<AbstractCommandResponse> commandResponseType = AbstractCommandResponse.class;
+
+        Assertions.assertThatIllegalArgumentException()
+                .isThrownBy(() -> CommandResponseHttpStatusValidator.validateHttpStatus(httpStatus,
+                        allowedHttpStatuses,
+                        commandResponseType))
+                .withMessage("%s is invalid. %s only allows %s.",
+                        httpStatus,
+                        commandResponseType.getSimpleName(),
+                        allowedHttpStatuses)
+                .withNoCause();
+    }
+
+}