org.springframework.web.servlet.view.AbstractCachingViewResolver Maven / Gradle / Ivy
/*
* Copyright 2002-2005 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.Collections;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import org.springframework.web.context.support.WebApplicationObjectSupport;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.ViewResolver;
/**
* Convenient superclass for view resolvers.
* Caches views once resolved: This means that view resolution won't be a
* performance problem, no matter how costly initial view retrieval is.
*
* View retrieval is deferred to subclasses via the loadView
* template method.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @see #loadView
*/
public abstract class AbstractCachingViewResolver extends WebApplicationObjectSupport implements ViewResolver {
/** Whether we should cache views, once resolved */
private boolean cache = true;
/** View name --> View instance */
private final Map viewMap = Collections.synchronizedMap(new HashMap());
/**
* Enable or disable caching. Disable this only for debugging and development.
* Default is for caching to be enabled.
*
Warning: Disabling caching can severely impact performance.
* Tests indicate that turning caching off reduces performance by at least 20%.
* Increased object churn probably eventually makes the problem even worse.
*/
public void setCache(boolean cache) {
this.cache = cache;
}
/**
* Return if caching is enabled.
*/
public boolean isCache() {
return cache;
}
public View resolveViewName(String viewName, Locale locale) throws Exception {
if (!this.cache) {
logger.warn("View caching is SWITCHED OFF -- DEVELOPMENT SETTING ONLY: This can severely impair performance");
return createView(viewName, locale);
}
else {
String cacheKey = getCacheKey(viewName, locale);
// No synchronization, as we can live with occasional double caching.
View view = (View) this.viewMap.get(cacheKey);
if (view == null) {
// Ask the subclass to create the View object.
view = createView(viewName, locale);
this.viewMap.put(cacheKey, view);
if (logger.isDebugEnabled()) {
logger.debug("Cached view '" + cacheKey + "'");
}
}
return view;
}
}
/**
* Provides functionality to clear the cache for a certain view.
* This can be handy in case developer are able to modify views
* (e.g. Velocity templates) at runtime after which you'd need to
* clear the cache for the specified view.
* @param viewName the view name for which the cached view object
* (if any) needs to be removed
* @param locale the locale for which the view object should be removed
*/
public void removeFromCache(String viewName, Locale locale) {
if (!this.cache) {
logger.warn("View caching is SWITCHED OFF -- removal not necessary");
}
else {
String cacheKey = getCacheKey(viewName, locale);
if (viewMap.remove(cacheKey) == null) {
// some debug output might be useful
if (logger.isDebugEnabled()) {
logger.debug("No cached instance for view '" + cacheKey + "' was found");
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Cach for view " + cacheKey + " has been cleared");
}
}
}
}
/**
* Return the cache key for the given viewName and the given locale.
* Needs to regard the locale in general, as a different locale can lead to a
* different view! Can be overridden in subclasses.
*/
protected String getCacheKey(String viewName, Locale locale) {
return viewName + "_" + locale;
}
/**
* Create the actual View object.
* Default implementation delegates to loadView.
*
Can be overridden to resolve certain view names in a special fashion,
* before delegating to the actual loadView implementation
* provided by the subclass.
* @param viewName the name of the view to retrieve
* @param locale the Locale to retrieve the view for
* @return the View instance, or null if not found
* (optional, to allow for ViewResolver chaining)
* @throws Exception if the view couldn't be resolved
* @see #loadView
*/
protected View createView(String viewName, Locale locale) throws Exception {
return loadView(viewName, locale);
}
/**
* Subclasses must implement this method. There need be no concern
* for efficiency, as this class will cache views.
*
Not all subclasses may support internationalization:
* A subclass that doesn't can simply ignore the locale parameter.
*
NOTE: As of Spring 1.2, subclasses are supposed to
* fully initialize the View objects before returning them,
* also applying bean container initialization callbacks.
* @param viewName the name of the view to retrieve
* @param locale the Locale to retrieve the view for
* @return the View instance, or null if not found
* (optional, to allow for ViewResolver chaining)
* @throws Exception if the view couldn't be resolved
* @see #resolveViewName
*/
protected abstract View loadView(String viewName, Locale locale) throws Exception;
}