/*
 * 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.handler;

import java.util.Set;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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

import org.springframework.core.Ordered;
import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;
import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.ModelAndView;

/**
 * Abstract base class for {@link HandlerExceptionResolver} implementations.
 *
 * <p>Supports mapped {@linkplain #setMappedHandlers handlers} and
 * {@linkplain #setMappedHandlerClasses handler classes} that the resolver
 * should be applied to and implements the {@link Ordered} interface.
 *
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since 3.0
 */
public abstract class AbstractHandlerExceptionResolver implements HandlerExceptionResolver, Ordered {

        private static final String HEADER_CACHE_CONTROL = "Cache-Control";


        /** Logger available to subclasses. */
        protected final Log logger = LogFactory.getLog(getClass());

        private int order = Ordered.LOWEST_PRECEDENCE;

        @Nullable
        private Set<?> mappedHandlers;

        @Nullable
        private Class<?>[] mappedHandlerClasses;

        @Nullable
        private Log warnLogger;

        private boolean preventResponseCaching = false;


        public void setOrder(int order) {
                this.order = order;
        }

        @Override
        public int getOrder() {
                return this.order;
        }

        /**
         * Specify the set of handlers that this exception resolver should apply to.
         * <p>The exception mappings and the default error view will only apply to the specified handlers.
         * <p>If no handlers or handler classes are set, the exception mappings and the default error
         * view will apply to all handlers. This means that a specified default error view will be used
         * as a fallback for all exceptions; any further HandlerExceptionResolvers in the chain will be
         * ignored in this case.
         */
        public void setMappedHandlers(Set<?> mappedHandlers) {
                this.mappedHandlers = mappedHandlers;
        }

        /**
         * Specify the set of classes that this exception resolver should apply to.
         * <p>The exception mappings and the default error view will only apply to handlers of the
         * specified types; the specified types may be interfaces or superclasses of handlers as well.
         * <p>If no handlers or handler classes are set, the exception mappings and the default error
         * view will apply to all handlers. This means that a specified default error view will be used
         * as a fallback for all exceptions; any further HandlerExceptionResolvers in the chain will be
         * ignored in this case.
         */
        public void setMappedHandlerClasses(Class<?>... mappedHandlerClasses) {
                this.mappedHandlerClasses = mappedHandlerClasses;
        }

        /**
         * Set the log category for warn logging. The name will be passed to the underlying logger
         * implementation through Commons Logging, getting interpreted as a log category according
         * to the logger's configuration. If {@code null} or empty String is passed, warn logging
         * is turned off.
         * <p>By default there is no warn logging although subclasses like
         * {@link org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver}
         * can change that default. Specify this setting to activate warn logging into a specific
         * category. Alternatively, override the {@link #logException} method for custom logging.
         * @see org.apache.commons.logging.LogFactory#getLog(String)
         * @see java.util.logging.Logger#getLogger(String)
         */
        public void setWarnLogCategory(String loggerName) {
                this.warnLogger = (StringUtils.hasLength(loggerName) ? LogFactory.getLog(loggerName) : null);
        }

        /**
         * Specify whether to prevent HTTP response caching for any view resolved
         * by this exception resolver.
         * <p>Default is {@code false}. Switch this to {@code true} in order to
         * automatically generate HTTP response headers that suppress response caching.
         */
        public void setPreventResponseCaching(boolean preventResponseCaching) {
                this.preventResponseCaching = preventResponseCaching;
        }


        /**
         * Check whether this resolver is supposed to apply (i.e. if the supplied handler
         * matches any of the configured {@linkplain #setMappedHandlers handlers} or
         * {@linkplain #setMappedHandlerClasses handler classes}), and then delegate
         * to the {@link #doResolveException} template method.
         */
        @Override
        @Nullable
        public ModelAndView resolveException(
                        HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {

                if (shouldApplyTo(request, handler)) {
                        prepareResponse(ex, response);
                        ModelAndView result = doResolveException(request, response, handler, ex);
                        if (result != null) {
                                // Print debug message when warn logger is not enabled.
                                if (logger.isDebugEnabled() && (this.warnLogger == null || !this.warnLogger.isWarnEnabled())) {
                                        logger.debug("Resolved [" + ex + "]" + (result.isEmpty() ? "" : " to " + result));
                                }
                                // Explicitly configured warn logger in logException method.
                                logException(ex, request);
                        }
                        return result;
                }
                else {
                        return null;
                }
        }

        /**
         * Check whether this resolver is supposed to apply to the given handler.
         * <p>The default implementation checks against the configured
         * {@linkplain #setMappedHandlers handlers} and
         * {@linkplain #setMappedHandlerClasses handler classes}, if any.
         * @param request current HTTP request
         * @param handler the executed handler, or {@code null} if none chosen
         * at the time of the exception (for example, if multipart resolution failed)
         * @return whether this resolved should proceed with resolving the exception
         * for the given request and handler
         * @see #setMappedHandlers
         * @see #setMappedHandlerClasses
         */
        protected boolean shouldApplyTo(HttpServletRequest request, @Nullable Object handler) {
                if (handler != null) {
                        if (this.mappedHandlers != null && this.mappedHandlers.contains(handler)) {
                                return true;
                        }
                        if (this.mappedHandlerClasses != null) {
                                for (Class<?> handlerClass : this.mappedHandlerClasses) {
                                        if (handlerClass.isInstance(handler)) {
                                                return true;
                                        }
                                }
                        }
                }
                // Else only apply if there are no explicit handler mappings.
                return (this.mappedHandlers == null && this.mappedHandlerClasses == null);
        }

        /**
         * Log the given exception at warn level, provided that warn logging has been
         * activated through the {@link #setWarnLogCategory "warnLogCategory"} property.
         * <p>Calls {@link #buildLogMessage} in order to determine the concrete message to log.
         * @param ex the exception that got thrown during handler execution
         * @param request current HTTP request (useful for obtaining metadata)
         * @see #setWarnLogCategory
         * @see #buildLogMessage
         * @see org.apache.commons.logging.Log#warn(Object, Throwable)
         */
        protected void logException(Exception ex, HttpServletRequest request) {
                if (this.warnLogger != null && this.warnLogger.isWarnEnabled()) {
                        this.warnLogger.warn(buildLogMessage(ex, request));
                }
        }

        /**
         * Build a log message for the given exception, occurred during processing the given request.
         * @param ex the exception that got thrown during handler execution
         * @param request current HTTP request (useful for obtaining metadata)
         * @return the log message to use
         */
        protected String buildLogMessage(Exception ex, HttpServletRequest request) {
                return "Resolved [" + ex + "]";
        }

        /**
         * Prepare the response for the exceptional case.
         * <p>The default implementation prevents the response from being cached,
         * if the {@link #setPreventResponseCaching "preventResponseCaching"} property
         * has been set to "true".
         * @param ex the exception that got thrown during handler execution
         * @param response current HTTP response
         * @see #preventCaching
         */
        protected void prepareResponse(Exception ex, HttpServletResponse response) {
                if (this.preventResponseCaching) {
                        preventCaching(response);
                }
        }

        /**
         * Prevents the response from being cached, through setting corresponding
         * HTTP {@code Cache-Control: no-store} header.
         * @param response current HTTP response
         */
        protected void preventCaching(HttpServletResponse response) {
                response.addHeader(HEADER_CACHE_CONTROL, "no-store");
        }


        /**
         * Actually resolve the given exception that got thrown during handler execution,
         * returning a {@link ModelAndView} that represents a specific error page if appropriate.
         * <p>May be overridden in subclasses, in order to apply specific exception checks.
         * Note that this template method will be invoked <i>after</i> checking whether this
         * resolved applies ("mappedHandlers" etc), so an implementation may simply proceed
         * with its actual exception handling.
         * @param request current HTTP request
         * @param response current HTTP response
         * @param handler the executed handler, or {@code null} if none chosen at the time
         * of the exception (for example, if multipart resolution failed)
         * @param ex the exception that got thrown during handler execution
         * @return a corresponding {@code ModelAndView} to forward to,
         * or {@code null} for default processing in the resolution chain
         */
        @Nullable
        protected abstract ModelAndView doResolveException(
                        HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex);

}