Introduce Servlet.fn

This commit introduces Servlet.fn, a servlet-based version of
WebFlux.fn, i.e. HandlerFunctions and RouterFunctions.

This commit contains the web framework only, further commits provide
tests and DispatcherServlet integration.

See spring-projectsgh-21490

Author: poutsma

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

@@ -0,0 +1,195 @@
+/*
+ * Copyright 2002-2019 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.servlet.function;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.function.Consumer;
+import javax.servlet.http.Cookie;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.springframework.core.Conventions;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
+import org.springframework.web.servlet.ModelAndView;
+
+/**
+ * Default {@link RenderingResponse.Builder} implementation.
+ *
+ * @author Arjen Poutsma
+ * @since 5.1
+ */
+final class DefaultRenderingResponseBuilder implements RenderingResponse.Builder {
+
+	private final String name;
+
+	private int status = HttpStatus.OK.value();
+
+	private final HttpHeaders headers = new HttpHeaders();
+
+	private final MultiValueMap<String, Cookie> cookies = new LinkedMultiValueMap<>();
+
+	private final Map<String, Object> model = new LinkedHashMap<>();
+
+
+	public DefaultRenderingResponseBuilder(RenderingResponse other) {
+		Assert.notNull(other, "RenderingResponse must not be null");
+		this.name = other.name();
+		this.status = (other instanceof DefaultRenderingResponse ?
+				((DefaultRenderingResponse) other).statusCode : other.statusCode().value());
+		this.headers.putAll(other.headers());
+		this.model.putAll(other.model());
+	}
+
+	public DefaultRenderingResponseBuilder(String name) {
+		Assert.notNull(name, "Name must not be null");
+		this.name = name;
+	}
+
+
+	@Override
+	public RenderingResponse.Builder status(HttpStatus status) {
+		Assert.notNull(status, "HttpStatus must not be null");
+		this.status = status.value();
+		return this;
+	}
+
+	@Override
+	public RenderingResponse.Builder status(int status) {
+		this.status = status;
+		return this;
+	}
+
+	@Override
+	public RenderingResponse.Builder cookie(Cookie cookie) {
+		Assert.notNull(cookie, "Cookie must not be null");
+		this.cookies.add(cookie.getName(), cookie);
+		return this;
+	}
+
+	@Override
+	public RenderingResponse.Builder cookies(Consumer<MultiValueMap<String, Cookie>> cookiesConsumer) {
+		cookiesConsumer.accept(this.cookies);
+		return this;
+	}
+
+	@Override
+	public RenderingResponse.Builder modelAttribute(Object attribute) {
+		Assert.notNull(attribute, "Attribute must not be null");
+		if (attribute instanceof Collection && ((Collection<?>) attribute).isEmpty()) {
+			return this;
+		}
+		return modelAttribute(Conventions.getVariableName(attribute), attribute);
+	}
+
+	@Override
+	public RenderingResponse.Builder modelAttribute(String name, @Nullable Object value) {
+		Assert.notNull(name, "Name must not be null");
+		this.model.put(name, value);
+		return this;
+	}
+
+	@Override
+	public RenderingResponse.Builder modelAttributes(Object... attributes) {
+		modelAttributes(Arrays.asList(attributes));
+		return this;
+	}
+
+	@Override
+	public RenderingResponse.Builder modelAttributes(Collection<?> attributes) {
+		attributes.forEach(this::modelAttribute);
+		return this;
+	}
+
+	@Override
+	public RenderingResponse.Builder modelAttributes(Map<String, ?> attributes) {
+		this.model.putAll(attributes);
+		return this;
+	}
+
+	@Override
+	public RenderingResponse.Builder header(String headerName, String... headerValues) {
+		for (String headerValue : headerValues) {
+			this.headers.add(headerName, headerValue);
+		}
+		return this;
+	}
+
+	@Override
+	public RenderingResponse.Builder headers(HttpHeaders headers) {
+		this.headers.putAll(headers);
+		return this;
+	}
+
+	@Override
+	public RenderingResponse build() {
+		return new DefaultRenderingResponse(this.status, this.headers, this.cookies, this.name, this.model);
+	}
+
+
+	private static final class DefaultRenderingResponse extends DefaultServerResponseBuilder.AbstractServerResponse
+			implements RenderingResponse {
+
+		private final String name;
+
+		private final Map<String, Object> model;
+
+		public DefaultRenderingResponse(int statusCode, HttpHeaders headers,
+				MultiValueMap<String, Cookie> cookies, String name, Map<String, Object> model) {
+
+			super(statusCode, headers, cookies);
+			this.name = name;
+			this.model = Collections.unmodifiableMap(new LinkedHashMap<>(model));
+		}
+
+		@Override
+		public String name() {
+			return this.name;
+		}
+
+		@Override
+		public Map<String, Object> model() {
+			return this.model;
+		}
+
+		@Override
+		protected ModelAndView writeToInternal(HttpServletRequest request,
+				HttpServletResponse response, Context context) {
+
+			HttpStatus status = HttpStatus.resolve(this.statusCode);
+			ModelAndView mav;
+			if (status != null) {
+				mav = new ModelAndView(this.name, status);
+			}
+			else {
+				mav = new ModelAndView(this.name);
+			}
+			mav.addAllObjects(this.model);
+			return mav;
+		}
+
+	}
+
+}