Polishing.

Allow nullable OffsetScrollPosition and add support for values wrapped within Optional.

Update tests. Reformat code. Add issue tags to tests.

See #2856
Original pull request: #2861

Author: mp911de

src/main/java/org/springframework/data/web/OffsetScrollPositionArgumentResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2023 the original author or authors.
+ * Copyright 2023 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.
@@ -17,7 +17,6 @@
 
 import org.springframework.core.MethodParameter;
 import org.springframework.data.domain.OffsetScrollPosition;
-import org.springframework.lang.NonNull;
 import org.springframework.lang.Nullable;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.bind.support.WebDataBinderFactory;
@@ -27,27 +26,31 @@
 
 /**
  * Argument resolver to extract a {@link OffsetScrollPosition} object from a {@link NativeWebRequest} for a particular
- * {@link MethodParameter}. A {@link OffsetScrollPositionArgumentResolver} can either resolve {@link OffsetScrollPosition} itself or wrap another
- * {@link OffsetScrollPositionArgumentResolver} to post-process {@link OffsetScrollPosition}.
+ * {@link MethodParameter}. A {@link OffsetScrollPositionArgumentResolver} can either resolve
+ * {@link OffsetScrollPosition} itself or wrap another {@link OffsetScrollPositionArgumentResolver} to post-process
+ * {@link OffsetScrollPosition}.
  *
- * @since 3.2
  * @author Yanming Zhou
- * @see HandlerMethodArgumentResolver
+ * @author Mark Paluch
+ * @since 3.2
+ * @see org.springframework.web.method.support.HandlerMethodArgumentResolver
  */
 public interface OffsetScrollPositionArgumentResolver extends HandlerMethodArgumentResolver {
 
 	/**
-	 * Resolves a {@link OffsetScrollPosition} method parameter into an argument value from a given request.
+	 * Resolves a {@link OffsetScrollPosition} method parameter into an argument value from a given request. Supports also
+	 * wrapped arguments in {@link java.util.Optional}.
 	 *
 	 * @param parameter the method parameter to resolve. This parameter must have previously been passed to
 	 *          {@link #supportsParameter} which must have returned {@code true}.
 	 * @param mavContainer the ModelAndViewContainer for the current request
 	 * @param webRequest the current request
 	 * @param binderFactory a factory for creating {@link WebDataBinder} instances
-	 * @return the resolved argument value
+	 * @return the resolved argument value or {@literal null} if the value cannot be resolved. The returned value
+	 *         considers {@link MethodParameter#isOptional() Optional} wrapping by returing either the value wrapped
+	 *         within Optional or Optional.empty().
 	 */
-	@NonNull
 	@Override
-	OffsetScrollPosition resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
+	Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
 			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory);
 }

src/main/java/org/springframework/data/web/OffsetScrollPositionHandlerMethodArgumentResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2023 the original author or authors.
+ * Copyright 2023 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.
@@ -15,6 +15,8 @@
  */
 package org.springframework.data.web;
 
+import java.util.Arrays;
+
 import org.springframework.core.MethodParameter;
 import org.springframework.data.domain.OffsetScrollPosition;
 import org.springframework.lang.Nullable;
@@ -23,27 +25,28 @@
 import org.springframework.web.method.support.HandlerMethodArgumentResolver;
 import org.springframework.web.method.support.ModelAndViewContainer;
 
-import java.util.Arrays;
-
 /**
- * {@link HandlerMethodArgumentResolver} to automatically create {@link OffsetScrollPosition} instances from request parameters.
+ * {@link HandlerMethodArgumentResolver} to automatically create {@link OffsetScrollPosition} instances from request
+ * parameters.
  *
- * @since 3.2
  * @author Yanming Zhou
+ * @since 3.2
  */
 public class OffsetScrollPositionHandlerMethodArgumentResolver extends OffsetScrollPositionHandlerMethodArgumentResolverSupport
 		implements OffsetScrollPositionArgumentResolver {
 
 	@Override
 	public boolean supportsParameter(MethodParameter parameter) {
-		return OffsetScrollPosition.class.equals(parameter.getParameterType());
+		return OffsetScrollPosition.class.equals(parameter.nestedIfOptional().getNestedParameterType());
 	}
 
 	@Override
-	public OffsetScrollPosition resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
+	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
 			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) {
 
-		String[] offsetParameter = webRequest.getParameterValues(getOffsetParameter(parameter));
-		return parseParameterIntoOffsetScrollPosition(offsetParameter != null ? Arrays.asList(offsetParameter) : null);
+		String[] offsetParameter = webRequest.getParameterValues(getOffsetParameter(parameter.nestedIfOptional()));
+		return adaptArgumentIfNecessary(
+				parseParameterIntoOffsetScrollPosition(offsetParameter != null ? Arrays.asList(offsetParameter) : null),
+				parameter);
 	}
 }

src/main/java/org/springframework/data/web/OffsetScrollPositionHandlerMethodArgumentResolverSupport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2023 the original author or authors.
+ * Copyright 2023 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.
@@ -15,22 +15,23 @@
  */
 package org.springframework.data.web;
 
+import java.util.List;
+import java.util.Optional;
+
 import org.springframework.core.MethodParameter;
 import org.springframework.data.domain.OffsetScrollPosition;
 import org.springframework.data.domain.ScrollPosition;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
 import org.springframework.util.StringUtils;
 
-import java.util.List;
-import java.util.Objects;
-
 /**
- * Base class providing methods for handler method argument resolvers to create {@link OffsetScrollPosition} instances from request
- * parameters.
+ * Base class providing methods for handler method argument resolvers to create {@link OffsetScrollPosition} instances
+ * from request parameters.
  *
- * @since 3.2
  * @author Yanming Zhou
+ * @since 3.2
  * @see OffsetScrollPositionHandlerMethodArgumentResolver
  * @see ReactiveOffsetScrollPositionHandlerMethodArgumentResolver
  */
@@ -71,7 +72,7 @@ public void setQualifierDelimiter(@Nullable String qualifierDelimiter) {
 	 * @param parameter can be {@literal null}.
 	 * @return the offset parameter
 	 */
-	protected String getOffsetParameter(@Nullable MethodParameter parameter) {
+	protected String getOffsetParameter(MethodParameter parameter) {
 
 		StringBuilder builder = new StringBuilder();
 
@@ -89,19 +90,39 @@ protected String getOffsetParameter(@Nullable MethodParameter parameter) {
 	 * Parses the given source into a {@link OffsetScrollPosition} instance.
 	 *
 	 * @param source could be {@literal null} or empty.
-	 * @return parsed OffsetScrollPosition
+	 * @return parsed OffsetScrollPosition or {@literal null} if it cannot be constructed.
 	 */
+	@Nullable
 	OffsetScrollPosition parseParameterIntoOffsetScrollPosition(@Nullable List<String> source) {
+
 		// No parameter or Single empty parameter, e.g "offset="
-		if (source == null || source.size() == 1 && !StringUtils.hasText(source.get(0))) {
-			return ScrollPosition.offset();
+		if (CollectionUtils.isEmpty(source) || (source.size() == 1 && !StringUtils.hasText(source.get(0)))) {
+			return null;
 		}
+
 		try {
 			long offset = Long.parseLong(source.get(0));
 			return ScrollPosition.offset(offset);
 		} catch (NumberFormatException ex) {
-			return ScrollPosition.offset();
+			return null;
 		}
 	}
 
+	/**
+	 * Adapt the given argument against the method parameter, if necessary.
+	 *
+	 * @param arg the resolved argument.
+	 * @param parameter the method parameter descriptor.
+	 * @return the adapted argument, or the original resolved argument as-is.
+	 */
+	@Nullable
+	Object adaptArgumentIfNecessary(@Nullable Object arg, MethodParameter parameter) {
+
+		if (parameter.getParameterType() == Optional.class) {
+			return arg == null ? Optional.empty() : Optional.of(arg);
+		}
+
+		return arg;
+	}
+
 }

src/main/java/org/springframework/data/web/ReactiveOffsetScrollPositionHandlerMethodArgumentResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2023 the original author or authors.
+ * Copyright 2023 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.
@@ -15,37 +15,36 @@
  */
 package org.springframework.data.web;
 
+import java.util.List;
+
 import org.springframework.core.MethodParameter;
 import org.springframework.data.domain.OffsetScrollPosition;
-import org.springframework.lang.NonNull;
 import org.springframework.web.reactive.BindingContext;
 import org.springframework.web.reactive.result.method.HandlerMethodArgumentResolver;
 import org.springframework.web.reactive.result.method.SyncHandlerMethodArgumentResolver;
 import org.springframework.web.server.ServerWebExchange;
 
-import java.util.List;
-
 /**
- * Reactive {@link HandlerMethodArgumentResolver} to create {@link OffsetScrollPosition} instances from query string parameters.
+ * Reactive {@link HandlerMethodArgumentResolver} to create {@link OffsetScrollPosition} instances from query string
+ * parameters.
  *
- * @since 3.2
  * @author Yanming Zhou
+ * @since 3.2
  */
-public class ReactiveOffsetScrollPositionHandlerMethodArgumentResolver extends OffsetScrollPositionHandlerMethodArgumentResolverSupport
-		implements SyncHandlerMethodArgumentResolver {
+public class ReactiveOffsetScrollPositionHandlerMethodArgumentResolver
+		extends OffsetScrollPositionHandlerMethodArgumentResolverSupport implements SyncHandlerMethodArgumentResolver {
 
 	@Override
 	public boolean supportsParameter(MethodParameter parameter) {
-		return OffsetScrollPosition.class.equals(parameter.getParameterType());
+		return OffsetScrollPosition.class.equals(parameter.nestedIfOptional().getNestedParameterType());
 	}
 
-	@NonNull
 	@Override
-	public OffsetScrollPosition resolveArgumentValue(MethodParameter parameter, BindingContext bindingContext,
+	public Object resolveArgumentValue(MethodParameter parameter, BindingContext bindingContext,
 			ServerWebExchange exchange) {
 
 		List<String> offsetParameter = exchange.getRequest().getQueryParams().get(getOffsetParameter(parameter));
 
-		return parseParameterIntoOffsetScrollPosition(offsetParameter);
+		return adaptArgumentIfNecessary(parseParameterIntoOffsetScrollPosition(offsetParameter), parameter);
 	}
 }