Restore fallback to request attributes in FreeMarker template model

Closes gh-29787

Author: jhoeller

spring-webmvc/src/main/java/org/springframework/web/servlet/view/AbstractTemplateView.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -66,14 +66,16 @@ public abstract class AbstractTemplateView extends AbstractUrlBasedView {
 	/**
 	 * Set whether all request attributes should be added to the
 	 * model prior to merging with the template. Default is "false".
+	 * <p>Note that some templates may make request attributes visible
+	 * on their own, e.g. FreeMarker, without exposure in the MVC model.
 	 */
 	public void setExposeRequestAttributes(boolean exposeRequestAttributes) {
 		this.exposeRequestAttributes = exposeRequestAttributes;
 	}
 
 	/**
 	 * Set whether HttpServletRequest attributes are allowed to override (hide)
-	 * controller generated model attributes of the same name. Default is "false",
+	 * controller generated model attributes of the same name. Default is "false"
 	 * which causes an exception to be thrown if request attributes of the same
 	 * name as model attributes are found.
 	 */
@@ -122,11 +124,11 @@ protected final void renderMergedOutputModel(
 				String attribute = en.nextElement();
 				if (model.containsKey(attribute) && !this.allowRequestOverride) {
 					throw new ServletException("Cannot expose request attribute '" + attribute +
-						"' because of an existing model object of the same name");
+							"' because of an existing model object of the same name");
 				}
 				Object attributeValue = request.getAttribute(attribute);
 				if (logger.isDebugEnabled()) {
-					exposed = exposed != null ? exposed : new LinkedHashMap<>();
+					exposed = (exposed != null ? exposed : new LinkedHashMap<>());
 					exposed.put(attribute, attributeValue);
 				}
 				model.put(attribute, attributeValue);
@@ -144,11 +146,11 @@ protected final void renderMergedOutputModel(
 					String attribute = en.nextElement();
 					if (model.containsKey(attribute) && !this.allowSessionOverride) {
 						throw new ServletException("Cannot expose session attribute '" + attribute +
-							"' because of an existing model object of the same name");
+								"' because of an existing model object of the same name");
 					}
 					Object attributeValue = session.getAttribute(attribute);
 					if (logger.isDebugEnabled()) {
-						exposed = exposed != null ? exposed : new LinkedHashMap<>();
+						exposed = (exposed != null ? exposed : new LinkedHashMap<>());
 						exposed.put(attribute, attributeValue);
 					}
 					model.put(attribute, attributeValue);

spring-webmvc/src/main/java/org/springframework/web/servlet/view/freemarker/FreeMarkerView.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -28,6 +28,8 @@
 import freemarker.template.SimpleHash;
 import freemarker.template.Template;
 import freemarker.template.TemplateException;
+import freemarker.template.TemplateModel;
+import freemarker.template.TemplateModelException;
 import jakarta.servlet.ServletContext;
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
@@ -59,6 +61,9 @@
  * of this approach.
  *
  * <p>Note: Spring's FreeMarker support requires FreeMarker 2.3 or higher.
+ * As of Spring Framework 6.0, FreeMarker templates are rendered in a minimal
+ * fashion without JSP support, just exposing request attributes in addition
+ * to the MVC-provided model map for alignment with common Servlet resources.
  *
  * @author Darren Davison
  * @author Juergen Hoeller
@@ -235,9 +240,6 @@ protected void exposeHelpers(Map<String, Object> model, HttpServletRequest reque
 	 * bean property, retrieved via {@code getTemplate}. It delegates to the
 	 * {@code processTemplate} method to merge the template instance with
 	 * the given template model.
-	 * <p>Adds the standard Freemarker hash models to the model: request parameters,
-	 * request, session and application (ServletContext), as well as the JSP tag
-	 * library hash model.
 	 * <p>Can be overridden to customize the behavior, for example to render
 	 * multiple templates into a single view.
 	 * @param model the model to use for rendering
@@ -256,7 +258,7 @@ protected void doRender(Map<String, Object> model, HttpServletRequest request,
 
 		// Expose model to JSP tags (as request attributes).
 		exposeModelAsRequestAttributes(model, request);
-		// Expose all standard FreeMarker hash models.
+		// Expose FreeMarker hash model.
 		SimpleHash fmModel = buildTemplateModel(model, request, response);
 
 		// Grab the locale-specific version of the template.
@@ -266,7 +268,8 @@ protected void doRender(Map<String, Object> model, HttpServletRequest request,
 
 	/**
 	 * Build a FreeMarker template model for the given model Map.
-	 * <p>The default implementation builds a {@link SimpleHash}.
+	 * <p>The default implementation builds a {@link SimpleHash} for the
+	 * given MVC model with an additional fallback to request attributes.
 	 * @param model the model to use for rendering
 	 * @param request current HTTP request
 	 * @param response current servlet response
@@ -275,7 +278,7 @@ protected void doRender(Map<String, Object> model, HttpServletRequest request,
 	protected SimpleHash buildTemplateModel(Map<String, Object> model, HttpServletRequest request,
 			HttpServletResponse response) {
 
-		SimpleHash fmModel = new SimpleHash(getObjectWrapper());
+		SimpleHash fmModel = new RequestHashModel(getObjectWrapper(), request);
 		fmModel.putAll(model);
 		return fmModel;
 	}
@@ -329,4 +332,34 @@ protected void processTemplate(Template template, SimpleHash model, HttpServletR
 		template.process(model, response.getWriter());
 	}
 
+
+	/**
+	 * Extension of FreeMarker {@link SimpleHash}, adding a fallback to request attributes.
+	 * Similar to the formerly used {@link freemarker.ext.servlet.AllHttpScopesHashModel},
+	 * just limited to common request attribute exposure.
+	 */
+	@SuppressWarnings("serial")
+	private static class RequestHashModel extends SimpleHash {
+
+		private final HttpServletRequest request;
+
+		public RequestHashModel(ObjectWrapper wrapper, HttpServletRequest request) {
+			super(wrapper);
+			this.request = request;
+		}
+
+		@Override
+		public TemplateModel get(String key) throws TemplateModelException {
+			TemplateModel model = super.get(key);
+			if (model != null) {
+				return model;
+			}
+			Object obj = this.request.getAttribute(key);
+			if (obj != null) {
+				return wrap(obj);
+			}
+			return wrap(null);
+		}
+	}
+
 }

spring-webmvc/src/test/java/org/springframework/web/servlet/view/freemarker/FreeMarkerViewTests.java

@@ -142,6 +142,33 @@ public void keepExistingContentType() throws Exception {
 		assertThat(response.getContentType()).isEqualTo("myContentType");
 	}
 
+	@Test
+	public void requestAttributeVisible() throws Exception {
+		FreeMarkerView fv = new FreeMarkerView();
+
+		WebApplicationContext wac = mock();
+		MockServletContext sc = new MockServletContext();
+
+		Map<String, FreeMarkerConfig> configs = new HashMap<>();
+		FreeMarkerConfigurer configurer = new FreeMarkerConfigurer();
+		configurer.setConfiguration(new TestConfiguration());
+		configs.put("configurer", configurer);
+		given(wac.getBeansOfType(FreeMarkerConfig.class, true, false)).willReturn(configs);
+		given(wac.getServletContext()).willReturn(sc);
+
+		fv.setUrl("templateName");
+		fv.setApplicationContext(wac);
+
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		request.addPreferredLocale(Locale.US);
+		request.setAttribute(DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE, wac);
+		request.setAttribute(DispatcherServlet.LOCALE_RESOLVER_ATTRIBUTE, new AcceptHeaderLocaleResolver());
+		HttpServletResponse response = new MockHttpServletResponse();
+
+		request.setAttribute("myattr", "myvalue");
+		fv.render(null, request, response);
+	}
+
 	@Test
 	public void freeMarkerViewResolver() throws Exception {
 		MockServletContext sc = new MockServletContext();
@@ -189,7 +216,7 @@ public void process(Object model, Writer writer) throws TemplateException, IOExc
 						assertThat(locale).isEqualTo(Locale.US);
 						assertThat(model instanceof SimpleHash).isTrue();
 						SimpleHash fmModel = (SimpleHash) model;
-						assertThat(fmModel.get("myattr").toString()).isEqualTo("myvalue");
+						assertThat(String.valueOf(fmModel.get("myattr"))).isEqualTo("myvalue");
 					}
 				};
 			}