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Jakarta Faces 3.0+ utility library
There is a newer version: 4.4.1
/*
 * Copyright OmniFaces
 *
 * 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.omnifaces.util.cache;

import static java.lang.Boolean.parseBoolean;
import static java.util.Collections.list;
import static org.omnifaces.util.Platform.getFacesServletRegistration;
import static org.omnifaces.util.Reflection.instance;

import java.util.HashMap;
import java.util.Map;

import jakarta.servlet.FilterRegistration;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletRegistration;

import org.omnifaces.ApplicationListener;
import org.omnifaces.filter.OnDemandResponseBufferFilter;

/**
 * Optional initializer for the {@link Cache} used by the Omnifaces Cache component.
 * 
 * It takes a configuration from web.xml context parameters and used that to set a cache provider and/or configure the
 * caching provider. If no initialization is done defaults are used.
 *
 * @since 1.1
 * @author Arjan Tijms
 * @see ApplicationListener
 */
public final class CacheInitializer {

	// Web context parameter to set the cache provider implementation
	public static final String CACHE_PROVIDER_INIT_PARAM_NAME = "org.omnifaces.CACHE_PROVIDER";
	public static final String CACHE_INSTALL_BUFFER_FILTER = "org.omnifaces.CACHE_INSTALL_BUFFER_FILTER";
	public static final String CACHE_PROVIDER_SETTING_INIT_PARAM_PREFIX = "org.omnifaces.CACHE_SETTING_";

	private CacheInitializer() {
		// Hide constructor.
	}

	public static void loadProviderAndRegisterFilter(ServletContext context) {

		// Check for a user configured custom cache provider, or get default one
		CacheProvider cacheProvider = getCacheProvider(context);

		// Build a map of settings for either the custom- or the default cache provider and set them.
		cacheProvider.setParameters(getCacheSetting(context));

		// Installs a filter that on demands buffers the response from the Faces Servlet, in order to grab child content
		// from the buffer.
		if (parseBoolean(context.getInitParameter(CACHE_INSTALL_BUFFER_FILTER))) {
			ServletRegistration facesServletRegistration = getFacesServletRegistration(context);
			FilterRegistration bufferFilterRegistration = context.addFilter(OnDemandResponseBufferFilter.class.getName(), OnDemandResponseBufferFilter.class);
			bufferFilterRegistration.addMappingForServletNames(null, true, facesServletRegistration.getName());
		}
	}

	private static CacheProvider getCacheProvider(ServletContext context) {
		CacheProvider cacheProvider;

		String cacheProviderName = context.getInitParameter(CACHE_PROVIDER_INIT_PARAM_NAME);
		if (cacheProviderName != null) {
			cacheProvider = instance(cacheProviderName);
			CacheFactory.setCacheProvider(cacheProvider, context);
		} else {
			cacheProvider = CacheFactory.getDefaultCacheProvider();
		}

		return cacheProvider;
	}

	private static Map getCacheSetting(ServletContext context) {
		Map settings = new HashMap<>();

		for (String initParameterName : list(context.getInitParameterNames())) {
			if (initParameterName.startsWith(CACHE_PROVIDER_SETTING_INIT_PARAM_PREFIX)) {
				settings.put(
					initParameterName.substring(CACHE_PROVIDER_SETTING_INIT_PARAM_PREFIX.length()),
					context.getInitParameter(initParameterName)
				);
			}
		}

		return settings;
	}

}