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Spring WebSocket
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/*
 * Copyright 2002-2017 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
 *
 *      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.springframework.web.socket.server.standard;

import java.util.Arrays;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import javax.websocket.server.ServerEndpoint;
import javax.websocket.server.ServerEndpointConfig.Configurator;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.lang.Nullable;
import org.springframework.stereotype.Component;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.web.context.ContextLoader;
import org.springframework.web.context.WebApplicationContext;

/**
 * A {@link javax.websocket.server.ServerEndpointConfig.Configurator} for initializing
 * {@link ServerEndpoint}-annotated classes through Spring.
 *
 * 
 * 
 * @ServerEndpoint(value = "/echo", configurator = SpringConfigurator.class)
 * public class EchoEndpoint {
 *     // ...
 * }
 * 
 *
 * @author Rossen Stoyanchev
 * @since 4.0
 * @see ServerEndpointExporter
 */
public class SpringConfigurator extends Configurator {

	private static final String NO_VALUE = ObjectUtils.identityToString(new Object());

	private static final Log logger = LogFactory.getLog(SpringConfigurator.class);

	private static final Map, String>> cache =
			new ConcurrentHashMap<>();


	@SuppressWarnings("unchecked")
	@Override
	public  T getEndpointInstance(Class endpointClass) throws InstantiationException {
		WebApplicationContext wac = ContextLoader.getCurrentWebApplicationContext();
		if (wac == null) {
			String message = "Failed to find the root WebApplicationContext. Was ContextLoaderListener not used?";
			logger.error(message);
			throw new IllegalStateException(message);
		}

		String beanName = ClassUtils.getShortNameAsProperty(endpointClass);
		if (wac.containsBean(beanName)) {
			T endpoint = wac.getBean(beanName, endpointClass);
			if (logger.isTraceEnabled()) {
				logger.trace("Using @ServerEndpoint singleton " + endpoint);
			}
			return endpoint;
		}

		Component ann = AnnotationUtils.findAnnotation(endpointClass, Component.class);
		if (ann != null && wac.containsBean(ann.value())) {
			T endpoint = wac.getBean(ann.value(), endpointClass);
			if (logger.isTraceEnabled()) {
				logger.trace("Using @ServerEndpoint singleton " + endpoint);
			}
			return endpoint;
		}

		beanName = getBeanNameByType(wac, endpointClass);
		if (beanName != null) {
			return (T) wac.getBean(beanName);
		}

		if (logger.isTraceEnabled()) {
			logger.trace("Creating new @ServerEndpoint instance of type " + endpointClass);
		}
		return wac.getAutowireCapableBeanFactory().createBean(endpointClass);
	}

	@Nullable
	private String getBeanNameByType(WebApplicationContext wac, Class endpointClass) {
		String wacId = wac.getId();

		Map, String> beanNamesByType = cache.get(wacId);
		if (beanNamesByType == null) {
			beanNamesByType = new ConcurrentHashMap<>();
			cache.put(wacId, beanNamesByType);
		}

		if (!beanNamesByType.containsKey(endpointClass)) {
			String[] names = wac.getBeanNamesForType(endpointClass);
			if (names.length == 1) {
				beanNamesByType.put(endpointClass, names[0]);
			}
			else {
				beanNamesByType.put(endpointClass, NO_VALUE);
				if (names.length > 1) {
					throw new IllegalStateException("Found multiple @ServerEndpoint's of type [" +
							endpointClass.getName() + "]: bean names " + Arrays.asList(names));
				}
			}
		}

		String beanName = beanNamesByType.get(endpointClass);
		return (NO_VALUE.equals(beanName) ? null : beanName);
	}

}