/*
 * Copyright 2002-2019 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.mvc;

import java.util.Enumeration;
import java.util.Properties;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ReflectionUtils;
import org.springframework.web.servlet.ModelAndView;

/**
 * Spring Controller implementation that wraps a servlet instance which it manages
 * internally. Such a wrapped servlet is not known outside of this controller;
 * its entire lifecycle is covered here (in contrast to {@link ServletForwardingController}).
 *
 * <p>Useful to invoke an existing servlet via Spring's dispatching infrastructure,
 * for example to apply Spring HandlerInterceptors to its requests.
 *
 * <p>Note that Struts has a special requirement in that it parses {@code web.xml}
 * to find its servlet mapping. Therefore, you need to specify the DispatcherServlet's
 * servlet name as "servletName" on this controller, so that Struts finds the
 * DispatcherServlet's mapping (thinking that it refers to the ActionServlet).
 *
 * <p><b>Example:</b> a DispatcherServlet XML context, forwarding "*.do" to the Struts
 * ActionServlet wrapped by a ServletWrappingController. All such requests will go
 * through the configured HandlerInterceptor chain (e.g. an OpenSessionInViewInterceptor).
 * From the Struts point of view, everything will work as usual.
 *
 * <pre class="code">
 * &lt;bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"&gt;
 *   &lt;property name="interceptors"&gt;
 *     &lt;list&gt;
 *       &lt;ref bean="openSessionInViewInterceptor"/&gt;
 *     &lt;/list&gt;
 *   &lt;/property&gt;
 *   &lt;property name="mappings"&gt;
 *     &lt;props&gt;
 *       &lt;prop key="*.do"&gt;strutsWrappingController&lt;/prop&gt;
 *     &lt;/props&gt;
 *   &lt;/property&gt;
 * &lt;/bean&gt;
 *
 * &lt;bean id="strutsWrappingController" class="org.springframework.web.servlet.mvc.ServletWrappingController"&gt;
 *   &lt;property name="servletClass"&gt;
 *     &lt;value&gt;org.apache.struts.action.ActionServlet&lt;/value&gt;
 *   &lt;/property&gt;
 *   &lt;property name="servletName"&gt;
 *     &lt;value&gt;action&lt;/value&gt;
 *   &lt;/property&gt;
 *   &lt;property name="initParameters"&gt;
 *     &lt;props&gt;
 *       &lt;prop key="config"&gt;/WEB-INF/struts-config.xml&lt;/prop&gt;
 *     &lt;/props&gt;
 *   &lt;/property&gt;
 * &lt;/bean&gt;</pre>
 *
 * @author Juergen Hoeller
 * @since 1.1.1
 * @see ServletForwardingController
 */
public class ServletWrappingController extends AbstractController
                implements BeanNameAware, InitializingBean, DisposableBean {

        @Nullable
        private Class<? extends Servlet> servletClass;

        @Nullable
        private String servletName;

        private Properties initParameters = new Properties();

        @Nullable
        private String beanName;

        @Nullable
        private Servlet servletInstance;


        public ServletWrappingController() {
                super(false);
        }


        /**
         * Set the class of the servlet to wrap.
         * Needs to implement {@code javax.servlet.Servlet}.
         * @see javax.servlet.Servlet
         */
        public void setServletClass(Class<? extends Servlet> servletClass) {
                this.servletClass = servletClass;
        }

        /**
         * Set the name of the servlet to wrap.
         * Default is the bean name of this controller.
         */
        public void setServletName(String servletName) {
                this.servletName = servletName;
        }

        /**
         * Specify init parameters for the servlet to wrap,
         * as name-value pairs.
         */
        public void setInitParameters(Properties initParameters) {
                this.initParameters = initParameters;
        }

        @Override
        public void setBeanName(String name) {
                this.beanName = name;
        }


        /**
         * Initialize the wrapped Servlet instance.
         * @see javax.servlet.Servlet#init(javax.servlet.ServletConfig)
         */
        @Override
        public void afterPropertiesSet() throws Exception {
                if (this.servletClass == null) {
                        throw new IllegalArgumentException("'servletClass' is required");
                }
                if (this.servletName == null) {
                        this.servletName = this.beanName;
                }
                this.servletInstance = ReflectionUtils.accessibleConstructor(this.servletClass).newInstance();
                this.servletInstance.init(new DelegatingServletConfig());
        }


        /**
         * Invoke the wrapped Servlet instance.
         * @see javax.servlet.Servlet#service(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
         */
        @Override
        protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
                        throws Exception {

                Assert.state(this.servletInstance != null, "No Servlet instance");
                this.servletInstance.service(request, response);
                return null;
        }


        /**
         * Destroy the wrapped Servlet instance.
         * @see javax.servlet.Servlet#destroy()
         */
        @Override
        public void destroy() {
                if (this.servletInstance != null) {
                        this.servletInstance.destroy();
                }
        }


        /**
         * Internal implementation of the ServletConfig interface, to be passed
         * to the wrapped servlet. Delegates to ServletWrappingController fields
         * and methods to provide init parameters and other environment info.
         */
        private class DelegatingServletConfig implements ServletConfig {

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

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

                @Override
                public String getInitParameter(String paramName) {
                        return initParameters.getProperty(paramName);
                }

                @Override
                @SuppressWarnings({"rawtypes", "unchecked"})
                public Enumeration<String> getInitParameterNames() {
                        return (Enumeration) initParameters.keys();
                }
        }

}