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Spring Framework example source code file (AbstractCachingViewResolver.java)

This example Spring Framework source code file (AbstractCachingViewResolver.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Spring Framework tags/keywords

cached, clearing, exception, exception, locale, locale, object, object, off, switched, util, view, view, viewresolver, webapplicationobjectsupport

The Spring Framework AbstractCachingViewResolver.java source code

/*
 * Copyright 2002-2007 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.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 base class for {@link org.springframework.web.servlet.ViewResolver}
 * implementations. Caches {@link org.springframework.web.servlet.View} objects
 * once resolved: This means that view resolution won't be a performance problem,
 * no matter how costly initial view retrieval is.
 *
 * <p>Subclasses need to implement the {@link #loadView} template method,
 * building the View object for a specific view name and locale.
 *
 * @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;

	/** Map from view name to View instance */
	private final Map viewCache = new HashMap();


	/**
	 * Enable or disable caching.
	 * <p>Default is "true": caching is enabled.
	 * Disable this only for debugging and development.
	 * <p>Warning: Disabling caching can severely impact performance.
	 */
	public void setCache(boolean cache) {
		this.cache = cache;
	}

	/**
	 * Return if caching is enabled.
	 */
	public boolean isCache() {
		return this.cache;
	}


	public View resolveViewName(String viewName, Locale locale) throws Exception {
		if (!isCache()) {
			logger.warn("View caching is SWITCHED OFF -- DEVELOPMENT SETTING ONLY: This can severely impair performance");
			return createView(viewName, locale);
		}
		else {
			Object cacheKey = getCacheKey(viewName, locale);
			synchronized (this.viewCache) {
				View view = (View) this.viewCache.get(cacheKey);
				if (view == null) {
					// Ask the subclass to create the View object.
					view = createView(viewName, locale);
					this.viewCache.put(cacheKey, view);
					if (logger.isDebugEnabled()) {
						logger.debug("Cached view [" + cacheKey + "]");
					}
				}
				return view;
			}
		}
	}

	/**
	 * Return the cache key for the given view name and the given locale.
	 * <p>Default is a String consisting of view name and locale suffix.
	 * Can be overridden in subclasses.
	 * <p>Needs to respect the locale in general, as a different locale can
	 * lead to a different view resource.
	 */
	protected Object getCacheKey(String viewName, Locale locale) {
		return viewName + "_" + locale;
	}

	/**
	 * Provides functionality to clear the cache for a certain view.
	 * <p>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 {
			Object cacheKey = getCacheKey(viewName, locale);
			Object cachedView = null;
			synchronized (this.viewCache) {
				cachedView = this.viewCache.remove(cacheKey);
			}
			if (cachedView == 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("Cache for view " + cacheKey + " has been cleared");
				}
			}
		}
	}

	/**
	 * Clear the entire view cache, removing all cached view objects.
	 * Subsequent resolve calls will lead to recreation of demanded view objects.
	 */
	public void clearCache() {
		logger.debug("Clearing entire view cache");
		synchronized (this.viewCache) {
			this.viewCache.clear();
		}
	}


	/**
	 * Create the actual View object.
	 * <p>The default implementation delegates to {@link #loadView}.
	 * This can be overridden to resolve certain view names in a special fashion,
	 * before delegating to the actual <code>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 <code>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, building a View object
	 * for the specified view. The returned View objects will be
	 * cached by this ViewResolver base class.
	 * <p>Subclasses are not forced to support internationalization:
	 * A subclass that does not may simply ignore the locale parameter.
	 * @param viewName the name of the view to retrieve
	 * @param locale the Locale to retrieve the view for
	 * @return the View instance, or <code>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;

}

Other Spring Framework examples (source code examples)

Here is a short list of links related to this Spring Framework AbstractCachingViewResolver.java source code file:

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