Java tutorial
/* * Copyright 2002-2016 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 * * https://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.view; import java.util.Enumeration; import java.util.LinkedHashMap; import java.util.Map; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import org.springframework.web.servlet.support.RequestContext; /** * Adapter base class for template-based view technologies such as FreeMarker, * with the ability to use request and session attributes in their model and * the option to expose helper objects for Spring's FreeMarker macro library. * * <p>JSP/JSTL and other view technologies automatically have access to the * HttpServletRequest object and thereby the request/session attributes * for the current user. Furthermore, they are able to create and cache * helper objects as request attributes themselves. * * @author Juergen Hoeller * @author Darren Davison * @since 1.0.2 * @see AbstractTemplateViewResolver * @see org.springframework.web.servlet.view.freemarker.FreeMarkerView */ public abstract class AbstractTemplateView extends AbstractUrlBasedView { /** * Variable name of the RequestContext instance in the template model, * available to Spring's macros: e.g. for creating BindStatus objects. */ public static final String SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE = "springMacroRequestContext"; private boolean exposeRequestAttributes = false; private boolean allowRequestOverride = false; private boolean exposeSessionAttributes = false; private boolean allowSessionOverride = false; private boolean exposeSpringMacroHelpers = true; /** * Set whether all request attributes should be added to the * model prior to merging with the template. Default is "false". */ 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", * which causes an exception to be thrown if request attributes of the same * name as model attributes are found. */ public void setAllowRequestOverride(boolean allowRequestOverride) { this.allowRequestOverride = allowRequestOverride; } /** * Set whether all HttpSession attributes should be added to the * model prior to merging with the template. Default is "false". */ public void setExposeSessionAttributes(boolean exposeSessionAttributes) { this.exposeSessionAttributes = exposeSessionAttributes; } /** * Set whether HttpSession attributes are allowed to override (hide) * controller generated model attributes of the same name. Default is "false", * which causes an exception to be thrown if session attributes of the same * name as model attributes are found. */ public void setAllowSessionOverride(boolean allowSessionOverride) { this.allowSessionOverride = allowSessionOverride; } /** * Set whether to expose a RequestContext for use by Spring's macro library, * under the name "springMacroRequestContext". Default is "true". * <p>Currently needed for Spring's FreeMarker default macros. * Note that this is <i>not</i> required for templates that use HTML forms * <i>unless</i> you wish to take advantage of the Spring helper macros. * @see #SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE */ public void setExposeSpringMacroHelpers(boolean exposeSpringMacroHelpers) { this.exposeSpringMacroHelpers = exposeSpringMacroHelpers; } @Override protected final void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception { if (this.exposeRequestAttributes) { Map<String, Object> exposed = null; for (Enumeration<String> en = request.getAttributeNames(); en.hasMoreElements();) { 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"); } Object attributeValue = request.getAttribute(attribute); if (logger.isDebugEnabled()) { exposed = exposed != null ? exposed : new LinkedHashMap<>(); exposed.put(attribute, attributeValue); } model.put(attribute, attributeValue); } if (logger.isTraceEnabled() && exposed != null) { logger.trace("Exposed request attributes to model: " + exposed); } } if (this.exposeSessionAttributes) { HttpSession session = request.getSession(false); if (session != null) { Map<String, Object> exposed = null; for (Enumeration<String> en = session.getAttributeNames(); en.hasMoreElements();) { 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"); } Object attributeValue = session.getAttribute(attribute); if (logger.isDebugEnabled()) { exposed = exposed != null ? exposed : new LinkedHashMap<>(); exposed.put(attribute, attributeValue); } model.put(attribute, attributeValue); } if (logger.isTraceEnabled() && exposed != null) { logger.trace("Exposed session attributes to model: " + exposed); } } } if (this.exposeSpringMacroHelpers) { if (model.containsKey(SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE)) { throw new ServletException( "Cannot expose bind macro helper '" + SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE + "' because of an existing model object of the same name"); } // Expose RequestContext instance for Spring macros. model.put(SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE, new RequestContext(request, response, getServletContext(), model)); } applyContentType(response); if (logger.isDebugEnabled()) { logger.debug("Rendering [" + getUrl() + "]"); } renderMergedTemplateModel(model, request, response); } /** * Apply this view's content type as specified in the "contentType" * bean property to the given response. * <p>Only applies the view's contentType if no content type has been * set on the response before. This allows handlers to override the * default content type beforehand. * @param response current HTTP response * @see #setContentType */ protected void applyContentType(HttpServletResponse response) { if (response.getContentType() == null) { response.setContentType(getContentType()); } } /** * Subclasses must implement this method to actually render the view. * @param model combined output Map, with request attributes and * session attributes merged into it if required * @param request current HTTP request * @param response current HTTP response * @throws Exception if rendering failed */ protected abstract void renderMergedTemplateModel(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception; }