Add Thymeleaf ViewResolver for Web Flow

The classes are copied from thymeleaf-spring5, temporarily here until
they become available in thymeleaf-spring6.

Author: rstoyanchev

booking-mvc/src/main/java/org/thymeleaf/spring6/view/AjaxEnabledView.java

@@ -0,0 +1,82 @@
+/*
+ * =============================================================================
+ *
+ *   Copyright (c) 2011-2018, The THYMELEAF team (http://www.thymeleaf.org)
+ *
+ *   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.thymeleaf.spring6.view;
+
+import org.springframework.web.servlet.View;
+import org.springframework.webflow.context.servlet.AjaxHandler;
+
+
+// Copied from thymeleaf-spring5.
+// Temporarily here until available in thymeleaf-spring6.
+
+
+/**
+ * <p>
+ *   Interface defining getter and setter methods for an
+ *   {@code ajaxHandler} property in Views, so that they can
+ *   be used in Spring AJAX environments.
+ * </p>
+ *
+ * @author Daniel Fern&aacute;ndez
+ *
+ * @since 3.0.3
+ *
+ */
+public interface AjaxEnabledView extends View {
+
+
+
+	/**
+	 * <p>
+	 *   Return the AJAX handler (from Spring Javascript) used
+	 *   to determine whether a request is an AJAX request or not.
+	 * </p>
+	 * <p>
+	 *   Views implementing this interface should be used with an instance of
+	 *   {@link AjaxThymeleafViewResolver} or any of its subclasses,
+	 *   so that {@link #setAjaxHandler(AjaxHandler)} can be called by
+	 *   the resolver when resolving the view, setting the default
+	 *   AJAX handler being used.
+	 * </p>
+	 *
+	 * @return the AJAX handler.
+	 */
+	public AjaxHandler getAjaxHandler();
+
+
+	/**
+	 * <p>
+	 *   Sets the AJAX handler (from Spring Javascript) used
+	 *   to determine whether a request is an AJAX request or not.
+	 * </p>
+	 * <p>
+	 *   Views implementing this interface should be used with an instance of
+	 *   {@link AjaxThymeleafViewResolver} or any of its subclasses,
+	 *   so that this method can be called by
+	 *   the resolver when resolving the view, setting the default
+	 *   AJAX handler being used.
+	 * </p>
+	 *
+	 * @param ajaxHandler the AJAX handler.
+	 */
+	public void setAjaxHandler(final AjaxHandler ajaxHandler);
+
+
+}

booking-mvc/src/main/java/org/thymeleaf/spring6/view/AjaxThymeleafView.java

@@ -0,0 +1,144 @@
+/*
+ * =============================================================================
+ *
+ *   Copyright (c) 2011-2018, The THYMELEAF team (http://www.thymeleaf.org)
+ *
+ *   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.thymeleaf.spring6.view;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.util.StringUtils;
+import org.springframework.webflow.context.servlet.AjaxHandler;
+import org.thymeleaf.exceptions.ConfigurationException;
+
+
+// Copied from thymeleaf-spring5.
+// Temporarily here until available in thymeleaf-spring6.
+
+
+/**
+ * <p>
+ *   Subclass of {@link ThymeleafView} adding compatibility with AJAX events in
+ *   Spring JavaScript (part of Spring WebFlow). This allows this View implementation
+ *   to be able to return only <i>fragments</i> of the page.
+ * </p>
+ * <p>
+ *   These rendering of fragments is used, for example, in Spring WebFlow's &lt;render&gt;
+ *   instructions (though not only).
+ * </p>
+ * <p>
+ *   This view searches for a comma-separated list of <i>markup selectors</i> in a request
+ *   parameter called {@code fragments}.
+ * </p>
+ *
+ * @author Daniel Fern&aacute;ndez
+ *
+ * @since 3.0.3
+ *
+ */
+public class AjaxThymeleafView extends ThymeleafView implements AjaxEnabledView {
+
+	private static final Logger vlogger = LoggerFactory.getLogger(AjaxThymeleafView.class);
+
+	private static final String FRAGMENTS_PARAM = "fragments";
+
+
+	private AjaxHandler ajaxHandler = null;
+
+
+
+	public AjaxThymeleafView() {
+		super();
+	}
+
+
+
+	public AjaxHandler getAjaxHandler() {
+		return this.ajaxHandler;
+	}
+
+
+	public void setAjaxHandler(final AjaxHandler ajaxHandler) {
+		this.ajaxHandler = ajaxHandler;
+	}
+
+
+
+
+	@Override
+	public void render(final Map<String, ?> model, final HttpServletRequest request, final HttpServletResponse response)
+			throws Exception {
+
+
+		final AjaxHandler templateAjaxHandler = getAjaxHandler();
+
+		if (templateAjaxHandler == null) {
+			throw new ConfigurationException("[THYMELEAF] AJAX Handler set into " +
+					AjaxThymeleafView.class.getSimpleName() + " instance for template " +
+					getTemplateName() + " is null.");
+		}
+
+		if (templateAjaxHandler.isAjaxRequest(request, response)) {
+
+			final Set<String> fragmentsToRender = getRenderFragments(model, request, response);
+			if (fragmentsToRender == null || fragmentsToRender.size() == 0) {
+				vlogger.warn("[THYMELEAF] An Ajax request was detected, but no fragments were specified to be re-rendered.  "
+						+ "Falling back to full page render.  This can cause unpredictable results when processing "
+						+ "the ajax response on the client.");
+				super.render(model, request, response);
+				return;
+			}
+
+			super.renderFragment(fragmentsToRender, model, request, response);
+
+		} else {
+
+			super.render(model, request, response);
+
+		}
+
+	}
+
+
+
+
+	@SuppressWarnings({ "rawtypes", "unused" })
+	protected Set<String> getRenderFragments(
+			final Map model, final HttpServletRequest request, final HttpServletResponse response) {
+		final String fragmentsParam = request.getParameter(FRAGMENTS_PARAM);
+		final String[] renderFragments = StringUtils.commaDelimitedListToStringArray(fragmentsParam);
+		if (renderFragments.length == 0) {
+			return null;
+		}
+		if (renderFragments.length == 1) {
+			return Collections.singleton(renderFragments[0]);
+		}
+		return new HashSet<String>(Arrays.asList(renderFragments));
+	}
+
+
+
+}