/*
* Copyright 2002-2008 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.view;
import java.util.Enumeration;
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.util.ClassUtils;
import org.springframework.web.servlet.support.RequestContext;
/**
* Adapter base class for template-based view technologies such as
* Velocity and FreeMarker, with the ability to use request and session
* attributes in their model and the option to expose helper objects
* for Spring's Velocity/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.velocity.VelocityView
* @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";
// Determine whether the Servlet 2.4 HttpServletResponse.getContentType()
// method is available.
private static boolean responseGetContentTypeAvailable =
ClassUtils.hasMethod(HttpServletResponse.class, "getContentType", new Class[0]);
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 Velocity and 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;
}
protected final void renderMergedOutputModel(
Map model, HttpServletRequest request, HttpServletResponse response) throws Exception {
if (this.exposeRequestAttributes) {
for (Enumeration en = request.getAttributeNames(); en.hasMoreElements();) {
String attribute = (String) 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()) {
logger.debug("Exposing request attribute '" + attribute +
"' with value [" + attributeValue + "] to model");
}
model.put(attribute, attributeValue);
}
}
if (this.exposeSessionAttributes) {
HttpSession session = request.getSession(false);
if (session != null) {
for (Enumeration en = session.getAttributeNames(); en.hasMoreElements();) {
String attribute = (String) 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()) {
logger.debug("Exposing session attribute '" + attribute +
"' with value [" + attributeValue + "] to model");
}
model.put(attribute, attributeValue);
}
}
}
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, getServletContext(), model));
}
applyContentType(response);
renderMergedTemplateModel(model, request, response);
}
/**
* Apply this view's content type as specified in the "contentType"
* bean property to the given response.
* <p>When running on Servlet 2.4, 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) {
boolean apply = true;
if (responseGetContentTypeAvailable) {
try {
apply = (response.getContentType() == null);
}
catch (Throwable ex) {
// Probably Servlet 2.4 API present but not implemented.
// Behave like on Servlet 2.3...
apply = true;
}
}
if (apply) {
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 model, HttpServletRequest request, HttpServletResponse response) throws Exception;
}