/*
 * 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.servlet.handler;

import java.util.Collections;
import java.util.Enumeration;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanInitializationException;
import org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor;
import org.springframework.lang.Nullable;
import org.springframework.web.context.ServletConfigAware;
import org.springframework.web.context.ServletContextAware;

/**
 * {@link org.springframework.beans.factory.config.BeanPostProcessor}
 * that applies initialization and destruction callbacks to beans that
 * implement the {@link javax.servlet.Servlet} interface.
 *
 * <p>After initialization of the bean instance, the Servlet {@code init}
 * method will be called with a ServletConfig that contains the bean name
 * of the Servlet and the ServletContext that it is running in.
 *
 * <p>Before destruction of the bean instance, the Servlet {@code destroy}
 * will be called.
 *
 * <p><b>Note that this post-processor does not support Servlet initialization
 * parameters.</b> Bean instances that implement the Servlet interface are
 * supposed to be configured like any other Spring bean, that is, through
 * constructor arguments or bean properties.
 *
 * <p>For reuse of a Servlet implementation in a plain Servlet container
 * and as a bean in a Spring context, consider deriving from Spring's
 * {@link org.springframework.web.servlet.HttpServletBean} base class that
 * applies Servlet initialization parameters as bean properties, supporting
 * both the standard Servlet and the Spring bean initialization style.
 *
 * <p><b>Alternatively, consider wrapping a Servlet with Spring's
 * {@link org.springframework.web.servlet.mvc.ServletWrappingController}.</b>
 * This is particularly appropriate for existing Servlet classes,
 * allowing to specify Servlet initialization parameters etc.
 *
 * @author Juergen Hoeller
 * @since 1.1.5
 * @see javax.servlet.Servlet#init(javax.servlet.ServletConfig)
 * @see javax.servlet.Servlet#destroy()
 * @see SimpleServletHandlerAdapter
 */
public class SimpleServletPostProcessor implements
                DestructionAwareBeanPostProcessor, ServletContextAware, ServletConfigAware {

        private boolean useSharedServletConfig = true;

        @Nullable
        private ServletContext servletContext;

        @Nullable
        private ServletConfig servletConfig;


        /**
         * Set whether to use the shared ServletConfig object passed in
         * through {@code setServletConfig}, if available.
         * <p>Default is "true". Turn this setting to "false" to pass in
         * a mock ServletConfig object with the bean name as servlet name,
         * holding the current ServletContext.
         * @see #setServletConfig
         */
        public void setUseSharedServletConfig(boolean useSharedServletConfig) {
                this.useSharedServletConfig = useSharedServletConfig;
        }

        @Override
        public void setServletContext(ServletContext servletContext) {
                this.servletContext = servletContext;
        }

        @Override
        public void setServletConfig(ServletConfig servletConfig) {
                this.servletConfig = servletConfig;
        }


        @Override
        public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
                return bean;
        }

        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
                if (bean instanceof Servlet) {
                        ServletConfig config = this.servletConfig;
                        if (config == null || !this.useSharedServletConfig) {
                                config = new DelegatingServletConfig(beanName, this.servletContext);
                        }
                        try {
                                ((Servlet) bean).init(config);
                        }
                        catch (ServletException ex) {
                                throw new BeanInitializationException("Servlet.init threw exception", ex);
                        }
                }
                return bean;
        }

        @Override
        public void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {
                if (bean instanceof Servlet) {
                        ((Servlet) bean).destroy();
                }
        }

        @Override
        public boolean requiresDestruction(Object bean) {
                return (bean instanceof Servlet);
        }


        /**
         * Internal implementation of the {@link ServletConfig} interface,
         * to be passed to the wrapped servlet.
         */
        private static class DelegatingServletConfig implements ServletConfig {

                private final String servletName;

                @Nullable
                private final ServletContext servletContext;

                public DelegatingServletConfig(String servletName, @Nullable ServletContext servletContext) {
                        this.servletName = servletName;
                        this.servletContext = servletContext;
                }

                @Override
                public String getServletName() {
                        return this.servletName;
                }

                @Override
                @Nullable
                public ServletContext getServletContext() {
                        return this.servletContext;
                }

                @Override
                @Nullable
                public String getInitParameter(String paramName) {
                        return null;
                }

                @Override
                public Enumeration<String> getInitParameterNames() {
                        return Collections.enumeration(Collections.emptySet());
                }
        }

}