Make getters and setters null-safety consistent

This commit ensure that null-safety is consistent between
getters and setters in order to be able to provide beans
with properties with a common type when type safety is
taken in account like with Kotlin.

It also add a few missing property level @Nullable
annotations.

Issue: SPR-15792

spring-webflux/src/main/java/org/springframework/web/reactive/config/WebFluxConfigurationSupport.java

@@ -90,7 +90,7 @@ public class WebFluxConfigurationSupport implements ApplicationContextAware {
 
 
 	@Override
-	public void setApplicationContext(ApplicationContext applicationContext) {
+	public void setApplicationContext(@Nullable ApplicationContext applicationContext) {
 		this.applicationContext = applicationContext;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/resource/PathResourceResolver.java

@@ -43,6 +43,7 @@ import org.springframework.web.server.ServerWebExchange;
  */
 public class PathResourceResolver extends AbstractResourceResolver {
 
+	@Nullable
 	private Resource[] allowedLocations;
 
 
@@ -61,7 +62,7 @@ public class PathResourceResolver extends AbstractResourceResolver {
 	 * to match its list of locations.
 	 * @param locations the list of allowed locations
 	 */
-	public void setAllowedLocations(Resource... locations) {
+	public void setAllowedLocations(@Nullable Resource... locations) {
 		this.allowedLocations = locations;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/resource/ResourceTransformerSupport.java

@@ -35,6 +35,7 @@ import org.springframework.web.server.ServerWebExchange;
  */
 public abstract class ResourceTransformerSupport implements ResourceTransformer {
 
+	@Nullable
 	private ResourceUrlProvider resourceUrlProvider;
 
 
@@ -45,7 +46,7 @@ public abstract class ResourceTransformerSupport implements ResourceTransformer
 	 * relative links.
 	 * @param resourceUrlProvider the URL provider to use
 	 */
-	public void setResourceUrlProvider(ResourceUrlProvider resourceUrlProvider) {
+	public void setResourceUrlProvider(@Nullable ResourceUrlProvider resourceUrlProvider) {
 		this.resourceUrlProvider = resourceUrlProvider;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/resource/ResourceWebHandler.java

@@ -95,8 +95,10 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 
 	private final List<ResourceTransformer> resourceTransformers = new ArrayList<>(4);
 
+	@Nullable
 	private CacheControl cacheControl;
 
+	@Nullable
 	private ResourceHttpMessageWriter resourceHttpMessageWriter;
 
 
@@ -160,7 +162,7 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 	 * Set the {@link org.springframework.http.CacheControl} instance to build
 	 * the Cache-Control HTTP response header.
 	 */
-	public void setCacheControl(CacheControl cacheControl) {
+	public void setCacheControl(@Nullable CacheControl cacheControl) {
 		this.cacheControl = cacheControl;
 	}
 
@@ -177,7 +179,7 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 	 * Configure the {@link ResourceHttpMessageWriter} to use.
 	 * <p>By default a {@link ResourceHttpMessageWriter} will be configured.
 	 */
-	public void setResourceHttpMessageWriter(ResourceHttpMessageWriter httpMessageWriter) {
+	public void setResourceHttpMessageWriter(@Nullable ResourceHttpMessageWriter httpMessageWriter) {
 		this.resourceHttpMessageWriter = httpMessageWriter;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/RequestMappingHandlerAdapter.java

@@ -76,7 +76,7 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, Application
 	 * Configure HTTP message readers to de-serialize the request body with.
 	 * <p>By default this is set to {@link ServerCodecConfigurer} with defaults.
 	 */
-	public void setMessageCodecConfigurer(ServerCodecConfigurer configurer) {
+	public void setMessageCodecConfigurer(@Nullable ServerCodecConfigurer configurer) {
 		this.messageCodecConfigurer = configurer;
 	}
 
@@ -92,7 +92,7 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, Application
 	 * Provide a WebBindingInitializer with "global" initialization to apply
 	 * to every DataBinder instance.
 	 */
-	public void setWebBindingInitializer(WebBindingInitializer webBindingInitializer) {
+	public void setWebBindingInitializer(@Nullable WebBindingInitializer webBindingInitializer) {
 		this.webBindingInitializer = webBindingInitializer;
 	}
 
@@ -107,8 +107,7 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, Application
 	/**
 	 * Configure resolvers for controller method arguments.
 	 */
-	public void setArgumentResolverConfigurer(ArgumentResolverConfigurer configurer) {
-		Assert.notNull(configurer, "ArgumentResolverConfigurer is required");
+	public void setArgumentResolverConfigurer(@Nullable ArgumentResolverConfigurer configurer) {
 		this.argumentResolverConfigurer = configurer;
 	}
 
@@ -125,7 +124,7 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, Application
 	 * <p>By default this is an instance of {@link ReactiveAdapterRegistry} with
 	 * default settings.
 	 */
-	public void setReactiveAdapterRegistry(ReactiveAdapterRegistry registry) {
+	public void setReactiveAdapterRegistry(@Nullable ReactiveAdapterRegistry registry) {
 		this.reactiveAdapterRegistry = registry;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/AbstractUrlBasedView.java

@@ -30,6 +30,7 @@ import org.springframework.lang.Nullable;
  */
 public abstract class AbstractUrlBasedView extends AbstractView implements InitializingBean {
 
+	@Nullable
 	private String url;
 
 
@@ -51,7 +52,7 @@ public abstract class AbstractUrlBasedView extends AbstractView implements Initi
 	 * Set the URL of the resource that this view wraps.
 	 * The URL must be appropriate for the concrete View implementation.
 	 */
-	public void setUrl(String url) {
+	public void setUrl(@Nullable String url) {
 		this.url = url;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/AbstractView.java

@@ -134,7 +134,7 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 	}
 
 	@Override
-	public void setApplicationContext(ApplicationContext applicationContext) {
+	public void setApplicationContext(@Nullable ApplicationContext applicationContext) {
 		this.applicationContext = applicationContext;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/RedirectView.java

@@ -111,9 +111,10 @@ public class RedirectView extends AbstractUrlBasedView {
 	 * {@link HttpStatus#TEMPORARY_REDIRECT} or
 	 * {@link HttpStatus#PERMANENT_REDIRECT}.
 	 */
-	public void setStatusCode(HttpStatus statusCode) {
-		Assert.notNull(statusCode, "HttpStatus must not be null");
-		Assert.isTrue(statusCode.is3xxRedirection(), "Must be a redirection (3xx status code)");
+	public void setStatusCode(@Nullable HttpStatus statusCode) {
+		if (statusCode != null) {
+			Assert.isTrue(statusCode.is3xxRedirection(), "Must be a redirection (3xx status code)");
+		}
 		this.statusCode = statusCode;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/UrlBasedViewResolver.java

@@ -73,18 +73,22 @@ public class UrlBasedViewResolver extends ViewResolverSupport
 	public static final String REDIRECT_URL_PREFIX = "redirect:";
 
 
+	@Nullable
 	private Class<?> viewClass;
 
 	private String prefix = "";
 
 	private String suffix = "";
 
+	@Nullable
 	private String[] viewNames;
 
 	private Function<String, RedirectView> redirectViewProvider = RedirectView::new;
 
+	@Nullable
 	private String requestContextAttribute;
 
+	@Nullable
 	private ApplicationContext applicationContext;
 
 
@@ -93,8 +97,8 @@ public class UrlBasedViewResolver extends ViewResolverSupport
 	 * @param viewClass a class that is assignable to the required view class
 	 * which by default is AbstractUrlBasedView
 	 */
-	public void setViewClass(Class<?> viewClass) {
-		if (!requiredViewClass().isAssignableFrom(viewClass)) {
+	public void setViewClass(@Nullable Class<?> viewClass) {
+		if (viewClass != null && !requiredViewClass().isAssignableFrom(viewClass)) {
 			String name = viewClass.getName();
 			throw new IllegalArgumentException("Given view class [" + name + "] " +
 					"is not of type [" + requiredViewClass().getName() + "]");
@@ -153,7 +157,7 @@ public class UrlBasedViewResolver extends ViewResolverSupport
 	 * 'my*', '*Report' and '*Repo*' will all match the view name 'myReport'.
 	 * @see #canHandle
 	 */
-	public void setViewNames(String... viewNames) {
+	public void setViewNames(@Nullable String... viewNames) {
 		this.viewNames = viewNames;
 	}
 
@@ -179,7 +183,7 @@ public class UrlBasedViewResolver extends ViewResolverSupport
 	 * @param requestContextAttribute name of the RequestContext attribute
 	 * @see AbstractView#setRequestContextAttribute
 	 */
-	public void setRequestContextAttribute(String requestContextAttribute) {
+	public void setRequestContextAttribute(@Nullable String requestContextAttribute) {
 		this.requestContextAttribute = requestContextAttribute;
 	}
 
@@ -200,7 +204,7 @@ public class UrlBasedViewResolver extends ViewResolverSupport
 	 * @see #applyLifecycleMethods
 	 */
 	@Override
-	public void setApplicationContext(ApplicationContext applicationContext) {
+	public void setApplicationContext(@Nullable ApplicationContext applicationContext) {
 		this.applicationContext = applicationContext;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/freemarker/FreeMarkerView.java

@@ -67,8 +67,10 @@ import org.springframework.web.server.ServerWebExchange;
  */
 public class FreeMarkerView extends AbstractUrlBasedView {
 
+	@Nullable
 	private Configuration configuration;
 
+	@Nullable
 	private String encoding;
 
 
@@ -78,7 +80,7 @@ public class FreeMarkerView extends AbstractUrlBasedView {
 	 * {@link FreeMarkerConfig} is expected in the Spring application context
 	 * which is used to obtain the FreeMarker configuration.
 	 */
-	public void setConfiguration(Configuration configuration) {
+	public void setConfiguration(@Nullable Configuration configuration) {
 		this.configuration = configuration;
 	}
 
@@ -109,7 +111,7 @@ public class FreeMarkerView extends AbstractUrlBasedView {
 	 * encoding in the FreeMarker Configuration rather than per template if all
 	 * your templates share a common encoding.
 	 */
-	public void setEncoding(String encoding) {
+	public void setEncoding(@Nullable String encoding) {
 		this.encoding = encoding;
 	}