UrlBasedViewResolverHDIV.java

/**
 * Copyright 2005-2010 hdiv.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.hdiv.web.servlet.view;

import java.util.Locale;

import org.springframework.web.servlet.View;
import org.springframework.web.servlet.view.AbstractUrlBasedView;
import org.springframework.web.servlet.view.InternalResourceView;
import org.springframework.web.servlet.view.UrlBasedViewResolver;

/**
 * Simple implementation of the {@link org.springframework.web.servlet.ViewResolver}
 * interface, allowing for direct resolution of symbolic view names to URLs,
 * without explicit mapping definition. This is useful if your symbolic names
 * match the names of your view resources in a straightforward manner
 * (i.e. the symbolic name is the unique part of the resource's filename),
 * without the need for a dedicated mapping to be defined for each view.
 *
 * <p>Supports {@link AbstractUrlBasedView} subclasses like {@link InternalResourceView},
 * {@link org.springframework.web.servlet.view.velocity.VelocityView} and
 * {@link org.springframework.web.servlet.view.freemarker.FreeMarkerView}.
 * The view class for all views generated by this resolver can be specified
 * via the "viewClass" property.
 *
 * <p>View names can either be resource URLs themselves, or get augmented by a
 * specified prefix and/or suffix. Exporting an attribute that holds the
 * RequestContext to all views is explicitly supported.
 *
 * <p>Example: prefix="/WEB-INF/jsp/", suffix=".jsp", viewname="test" ->
 * "/WEB-INF/jsp/test.jsp"
 *
 * <p>As a special feature, redirect URLs can be specified via the "redirect:"
 * prefix. E.g.: "redirect:myAction.do" will trigger a redirect to the given
 * URL, rather than resolution as standard view name. This is typically used
 * for redirecting to a controller URL after finishing a form workflow.
 *
 * <p>Furthermore, forward URLs can be specified via the "forward:" prefix. E.g.:
 * "forward:myAction.do" will trigger a forward to the given URL, rather than
 * resolution as standard view name. This is typically used for controller URLs;
 * it is not supposed to be used for JSP URLs - use logical view names there.
 *
 * <p><b>Note:</b> When chaining ViewResolvers, a UrlBasedViewResolver will check whether
 * the {@link AbstractUrlBasedView#checkResource specified resource actually exists}.
 * However, with {@link InternalResourceView}, it is not generally possible to
 * determine the existence of the target resource upfront. In such a scenario,
 * a UrlBasedViewResolver will always return View for any given view name;
 * as a consequence, it should be configured as the last ViewResolver in the chain.
 *
 * @author Gorka Vicente
 * @since HDIV 2.0.6
 * @see #setViewClass
 * @see #setPrefix
 * @see #setSuffix
 * @see #setRequestContextAttribute
 * @see #REDIRECT_URL_PREFIX
 * @see AbstractUrlBasedView
 * @see InternalResourceView
 * @see org.springframework.web.servlet.view.velocity.VelocityView
 * @see org.springframework.web.servlet.view.freemarker.FreeMarkerView
 */
public class UrlBasedViewResolverHDIV extends UrlBasedViewResolver {

	/**
	 * Overridden to implement check for "redirect:" prefix.
	 * <p>Not possible in <code>loadView</code>, since overridden
	 * <code>loadView</code> versions in subclasses might rely on the
	 * superclass always creating instances of the required view class.
	 * @see #loadView
	 * @see #requiredViewClass
	 */
	@Override
	protected View createView(String viewName, Locale locale) throws Exception {
		
		// If this resolver is not supposed to handle the given view,
		// return null to pass on to the next resolver in the chain.
		if (!canHandle(viewName, locale)) {
			return null;
		}
		// Check for special "redirect:" prefix.
		if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
			String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
			return new RedirectViewHDIV(redirectUrl, isRedirectContextRelative(), isRedirectHttp10Compatible());
		}
		// Check for special "forward:" prefix.
		if (viewName.startsWith(FORWARD_URL_PREFIX)) {
			String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
			return new InternalResourceView(forwardUrl);
		}
		// Else fall back to superclass implementation: calling loadView.
		return super.createView(viewName, locale);
	}

}