Add ServerRequest::checkNotModified

This commit adds the checkNotModified method to ServerRequest in both
WebFlux.fn and WebMvc.fn. Unlike other checkNotModified methods found
in the framework, this method does not return a boolean, but rather
a response wrapped in a Mono/Optional. If the resource has
not been changed, the not-modified response can be returned directly;
if the resource has changed, the user can create a corresponding
response using switchIfEmpty/orElse(Get).

Closes gh-24173

spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -17,15 +17,18 @@
 package org.springframework.web.servlet.function;
 
 import java.io.IOException;
+import java.io.PrintWriter;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.net.InetSocketAddress;
 import java.net.URI;
 import java.nio.charset.Charset;
 import java.security.Principal;
+import java.time.Instant;
 import java.util.AbstractMap;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
@@ -36,8 +39,10 @@ import java.util.Set;
 import java.util.stream.Collectors;
 
 import javax.servlet.ServletException;
+import javax.servlet.ServletOutputStream;
 import javax.servlet.http.Cookie;
 import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
 
 import org.springframework.core.ParameterizedTypeReference;
@@ -47,11 +52,14 @@ import org.springframework.http.MediaType;
 import org.springframework.http.converter.GenericHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.server.ServletServerHttpRequest;
+import org.springframework.lang.Nullable;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.HttpMediaTypeNotSupportedException;
+import org.springframework.web.context.request.ServletWebRequest;
+import org.springframework.web.context.request.WebRequest;
 import org.springframework.web.servlet.HandlerMapping;
 import org.springframework.web.servlet.support.ServletUriComponentsBuilder;
 import org.springframework.web.util.UriBuilder;
@@ -246,6 +254,26 @@ class DefaultServerRequest implements ServerRequest {
 		return Optional.ofNullable(this.serverHttpRequest.getPrincipal());
 	}
 
+	static Optional<ServerResponse> checkNotModified(HttpServletRequest servletRequest, @Nullable Instant lastModified,
+			@Nullable String etag) {
+
+		long lastModifiedTimestamp = -1;
+		if (lastModified != null && lastModified.isAfter(Instant.EPOCH)) {
+			lastModifiedTimestamp = lastModified.toEpochMilli();
+		}
+
+		CheckNotModifiedResponse response = new CheckNotModifiedResponse();
+		WebRequest webRequest = new ServletWebRequest(servletRequest, response);
+		if (webRequest.checkNotModified(etag, lastModifiedTimestamp)) {
+			return Optional.of(ServerResponse.status(response.status).
+					headers(headers -> headers.addAll(response.headers))
+					.build());
+		}
+		else {
+			return Optional.empty();
+		}
+	}
+
 	/**
 	 * Default implementation of {@link Headers}.
 	 */
@@ -419,4 +447,207 @@ class DefaultServerRequest implements ServerRequest {
 
 	}
 
+	/**
+	 * Simple implementation of {@link HttpServletResponse} used by
+	 * {@link #checkNotModified(HttpServletRequest, Instant, String)} to record status and headers set by
+	 * {@link ServletWebRequest#checkNotModified(String, long)}. Throws an {@code UnsupportedOperationException}
+	 * for other methods.
+	 */
+	@SuppressWarnings("deprecation")
+	private static final class CheckNotModifiedResponse implements HttpServletResponse {
+
+		private final HttpHeaders headers = new HttpHeaders();
+
+		private int status = 200;
+
+		@Override
+		public boolean containsHeader(String name) {
+			return this.headers.containsKey(name);
+		}
+
+		@Override
+		public void setDateHeader(String name, long date) {
+			this.headers.setDate(name, date);
+		}
+
+		@Override
+		public void setHeader(String name, String value) {
+			this.headers.set(name, value);
+		}
+
+		@Override
+		public void addHeader(String name, String value) {
+			this.headers.add(name, value);
+		}
+
+		@Override
+		public void setStatus(int sc) {
+			this.status = sc;
+		}
+
+		@Override
+		public void setStatus(int sc, String sm) {
+			this.status = sc;
+		}
+
+		@Override
+		public int getStatus() {
+			return this.status;
+		}
+
+		@Override
+		public String getHeader(String name) {
+			return this.headers.getFirst(name);
+		}
+
+		@Override
+		public Collection<String> getHeaders(String name) {
+			List<String> result = this.headers.get(name);
+			return result != null ? result : Collections.emptyList();
+		}
+
+		@Override
+		public Collection<String> getHeaderNames() {
+			return this.headers.keySet();
+		}
+
+
+		// Unsupported
+		@Override
+		public void addCookie(Cookie cookie) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public String encodeURL(String url) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public String encodeRedirectURL(String url) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public String encodeUrl(String url) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public String encodeRedirectUrl(String url) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void sendError(int sc, String msg) throws IOException {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void sendError(int sc) throws IOException {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void sendRedirect(String location) throws IOException {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void addDateHeader(String name, long date) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void setIntHeader(String name, int value) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void addIntHeader(String name, int value) {
+			throw new UnsupportedOperationException();
+		}
+
+
+		@Override
+		public String getCharacterEncoding() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public String getContentType() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public ServletOutputStream getOutputStream() throws IOException {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public PrintWriter getWriter() throws IOException {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void setCharacterEncoding(String charset) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void setContentLength(int len) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void setContentLengthLong(long len) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void setContentType(String type) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void setBufferSize(int size) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public int getBufferSize() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void flushBuffer() throws IOException {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void resetBuffer() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public boolean isCommitted() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void reset() {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public void setLocale(Locale loc) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public Locale getLocale() {
+			throw new UnsupportedOperationException();
+		}
+	}
+
 }

spring-webmvc/src/main/java/org/springframework/web/servlet/function/RequestPredicates.java

@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.net.InetSocketAddress;
 import java.net.URI;
 import java.security.Principal;
+import java.time.Instant;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -1017,6 +1018,21 @@ public abstract class RequestPredicates {
 			return this.request.servletRequest();
 		}
 
+		@Override
+		public Optional<ServerResponse> checkNotModified(Instant lastModified) {
+			return this.request.checkNotModified(lastModified);
+		}
+
+		@Override
+		public Optional<ServerResponse> checkNotModified(String etag) {
+			return this.request.checkNotModified(etag);
+		}
+
+		@Override
+		public Optional<ServerResponse> checkNotModified(Instant lastModified, String etag) {
+			return this.request.checkNotModified(lastModified, etag);
+		}
+
 		@Override
 		public String toString() {
 			return method() + " " +  path();

spring-webmvc/src/main/java/org/springframework/web/servlet/function/ServerRequest.java

@@ -21,6 +21,7 @@ import java.net.InetSocketAddress;
 import java.net.URI;
 import java.nio.charset.Charset;
 import java.security.Principal;
+import java.time.Instant;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -42,6 +43,7 @@ import org.springframework.http.MediaType;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.server.PathContainer;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.util.UriBuilder;
@@ -224,6 +226,109 @@ public interface ServerRequest {
 	 */
 	HttpServletRequest servletRequest();
 
+	/**
+	 * Check whether the requested resource has been modified given the
+	 * supplied last-modified timestamp (as determined by the application).
+	 * If not modified, this method returns a response with corresponding
+	 * status code and headers, otherwise an empty result.
+	 * <p>Typical usage:
+	 * <pre class="code">
+	 * public ServerResponse myHandleMethod(ServerRequest request) {
+	 *   Instant lastModified = // application-specific calculation
+	 *	 return request.checkNotModified(lastModified)
+	 *	   .orElseGet(() -> {
+	 *	     // further request processing, actually building content
+	 *		 return ServerResponse.ok().body(...);
+	 *	   });
+	 * }</pre>
+	 * <p>This method works with conditional GET/HEAD requests, but
+	 * also with conditional POST/PUT/DELETE requests.
+	 * <p><strong>Note:</strong> you can use either
+	 * this {@code #checkNotModified(Instant)} method; or
+	 * {@link #checkNotModified(String)}. If you want enforce both
+	 * a strong entity tag and a Last-Modified value,
+	 * as recommended by the HTTP specification,
+	 * then you should use {@link #checkNotModified(Instant, String)}.
+	 * @param lastModified the last-modified timestamp that the
+	 * application determined for the underlying resource
+	 * @return a corresponding response if the request qualifies as not
+	 * modified, or an empty result otherwise.
+	 * @since 5.2.5
+	 */
+	default Optional<ServerResponse> checkNotModified(Instant lastModified) {
+		Assert.notNull(lastModified, "LastModified must not be null");
+		return DefaultServerRequest.checkNotModified(servletRequest(), lastModified, null);
+	}
+
+	/**
+	 * Check whether the requested resource has been modified given the
+	 * supplied {@code ETag} (entity tag), as determined by the application.
+	 * If not modified, this method returns a response with corresponding
+	 * status code and headers, otherwise an empty result.
+	 * <p>Typical usage:
+	 * <pre class="code">
+	 * public ServerResponse myHandleMethod(ServerRequest request) {
+	 *   String eTag = // application-specific calculation
+	 *	 return request.checkNotModified(eTag)
+	 *	   .orElseGet(() -> {
+	 *	     // further request processing, actually building content
+	 *		 return ServerResponse.ok().body(...);
+	 *	   });
+	 * }</pre>
+	 * <p>This method works with conditional GET/HEAD requests, but
+	 * also with conditional POST/PUT/DELETE requests.
+	 * <p><strong>Note:</strong> you can use either
+	 * this {@link #checkNotModified(Instant)} method; or
+	 * {@code #checkNotModified(String)}. If you want enforce both
+	 * a strong entity tag and a Last-Modified value,
+	 * as recommended by the HTTP specification,
+	 * then you should use {@link #checkNotModified(Instant, String)}.
+	 * @param etag the entity tag that the application determined
+	 * for the underlying resource. This parameter will be padded
+	 * with quotes (") if necessary.
+	 * @return a corresponding response if the request qualifies as not
+	 * modified, or an empty result otherwise.
+	 * @since 5.2.5
+	 */
+	default Optional<ServerResponse> checkNotModified(String etag) {
+		Assert.notNull(etag, "Etag must not be null");
+		return DefaultServerRequest.checkNotModified(servletRequest(), null, etag);
+	}
+
+	/**
+	 * Check whether the requested resource has been modified given the
+	 * supplied {@code ETag} (entity tag) and last-modified timestamp,
+	 * as determined by the application.
+	 * If not modified, this method returns a response with corresponding
+	 * status code and headers, otherwise an empty result.
+	 * <p>Typical usage:
+	 * <pre class="code">
+	 * public ServerResponse myHandleMethod(ServerRequest request) {
+	 *   Instant lastModified = // application-specific calculation
+	 *   String eTag = // application-specific calculation
+	 *	 return request.checkNotModified(lastModified, eTag)
+	 *	   .orElseGet(() -> {
+	 *	     // further request processing, actually building content
+	 *		 return ServerResponse.ok().body(...);
+	 *	   });
+	 * }</pre>
+	 * <p>This method works with conditional GET/HEAD requests, but
+	 * also with conditional POST/PUT/DELETE requests.
+	 * @param lastModified the last-modified timestamp that the
+	 * application determined for the underlying resource
+	 * @param etag the entity tag that the application determined
+	 * for the underlying resource. This parameter will be padded
+	 * with quotes (") if necessary.
+	 * @return a corresponding response if the request qualifies as not
+	 * modified, or an empty result otherwise.
+	 * @since 5.2.5
+	 */
+	default Optional<ServerResponse> checkNotModified(Instant lastModified, String etag) {
+		Assert.notNull(lastModified, "LastModified must not be null");
+		Assert.notNull(etag, "Etag must not be null");
+		return DefaultServerRequest.checkNotModified(servletRequest(), lastModified, etag);
+	}
+
 
 	// Static methods
 
@@ -248,6 +353,7 @@ public interface ServerRequest {
 	}
 
 
+
 	/**
 	 * Represents the headers of the HTTP request.
 	 * @see ServerRequest#headers()