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Wicket is a Java web application framework that takes simplicity, separation of concerns and ease of development to a whole new level. Wicket pages can be mocked up, previewed and later revised using standard WYSIWYG HTML design tools. Dynamic content processing and form handling is all handled in Java code using a first-class component model backed by POJO data beans that can easily be persisted using your favorite technology.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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
 *
 *      http://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.apache.wicket;

import org.apache.wicket.authorization.AuthorizationException;
import org.apache.wicket.core.request.handler.IPageRequestHandler;
import org.apache.wicket.core.request.handler.ListenerInvocationNotAllowedException;
import org.apache.wicket.core.request.handler.PageProvider;
import org.apache.wicket.core.request.handler.RenderPageRequestHandler;
import org.apache.wicket.core.request.mapper.StalePageException;
import org.apache.wicket.markup.html.pages.ExceptionErrorPage;
import org.apache.wicket.protocol.http.PageExpiredException;
import org.apache.wicket.protocol.http.servlet.ResponseIOException;
import org.apache.wicket.request.IExceptionMapper;
import org.apache.wicket.request.IRequestHandler;
import org.apache.wicket.request.Request;
import org.apache.wicket.request.Response;
import org.apache.wicket.request.cycle.RequestCycle;
import org.apache.wicket.request.handler.EmptyRequestHandler;
import org.apache.wicket.request.http.WebRequest;
import org.apache.wicket.request.http.WebResponse;
import org.apache.wicket.request.http.handler.ErrorCodeRequestHandler;
import org.apache.wicket.request.resource.PackageResource;
import org.apache.wicket.settings.ExceptionSettings;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * If an exception is thrown when a page is being rendered this mapper will decide which error page
 * to show depending on the exception type and {@link Application#getExceptionSettings() application
 * configuration}
 */
public class DefaultExceptionMapper implements IExceptionMapper
{
	private static final Logger logger = LoggerFactory.getLogger(DefaultExceptionMapper.class);

	@Override
	public IRequestHandler map(Exception e)
	{
		try
		{
			Response response = RequestCycle.get().getResponse();
			// WICKET-7067 WebSocketResponse doesn't allow setting headers
			if (response instanceof WebResponse && ((WebResponse) response).isHeaderSupported())
			{
				// we don't want to cache an exceptional reply in the browser
				((WebResponse) response).disableCaching();
			}
			return internalMap(e);
		}
		catch (RuntimeException e2)
		{
			return handleNestedException(e, e2);
		}
	}


	/**
	 * Handles the case when an exception is generated while mapping the original exception happened
	 *
	 * @param originalException The original exception.
	 * @param nestedException The nested (second) exception produced
	 * @return IRequestHandler (by default ErrorCodeRequestHandler
	 */
	protected IRequestHandler handleNestedException(Exception originalException, RuntimeException nestedException)
	{
		if (logger.isDebugEnabled())
		{
			logger.error(
					"An error occurred while handling a previous error: " + nestedException.getMessage(), nestedException);
		}

		// hmmm, we were already handling an exception! give up
		logger.error("unexpected exception when handling another exception: " + originalException.getMessage(),
				originalException);
		return new ErrorCodeRequestHandler(500);
	}
	
	/**
	 * Maps exceptions to their corresponding {@link IRequestHandler}.
	 * 
	 * @param e
	 * 			the current exception
	 * @return the {@link IRequestHandler} for the current exception
	 */
	private IRequestHandler internalMap(Exception e)
	{
		final Application application = Application.get();

		// check if we are processing an Ajax request and if we want to invoke the failure handler
		if (isProcessingAjaxRequest())
		{
			switch (application.getExceptionSettings().getAjaxErrorHandlingStrategy())
			{
				case INVOKE_FAILURE_HANDLER :
					return new ErrorCodeRequestHandler(500);
			}
		}

		IRequestHandler handleExpectedExceptions = mapExpectedExceptions(e, application);
		
		if (handleExpectedExceptions != null)
		{
			return handleExpectedExceptions;
		}

		return mapUnexpectedExceptions(e, application);
	
	}
	
	/**
	 * Maps expected exceptions (i.e. those internally used by Wicket) to their corresponding
	 * {@link IRequestHandler}.
	 * 
	 * @param e
	 * 			the current exception
	 * @param application
	 * 			the current application object
	 * @return the {@link IRequestHandler} for the current exception
	 */
	protected IRequestHandler mapExpectedExceptions(Exception e, final Application application)
	{
		if (e instanceof StalePageException)
		{
			// If the page was stale, just re-render it
			// (the url should always be updated by an redirect in that case)
			return new RenderPageRequestHandler(new PageProvider(((StalePageException)e).getPage()));
		}
		else if (e instanceof PageExpiredException)
		{
			return createPageRequestHandler(new PageProvider(Application.get()
				.getApplicationSettings()
				.getPageExpiredErrorPage()));
		}
		else if (e instanceof AuthorizationException ||
			e instanceof ListenerInvocationNotAllowedException)
		{
			return createPageRequestHandler(new PageProvider(Application.get()
				.getApplicationSettings()
				.getAccessDeniedPage()));
		}
		else if (e instanceof ResponseIOException)
		{
			logger.debug("Connection lost, give up responding.", e);
			return new EmptyRequestHandler();
		}
		else if (e instanceof PackageResource.PackageResourceBlockedException && application.usesDeploymentConfig())
		{
			logger.debug(e.getMessage(), e);
			return new ErrorCodeRequestHandler(404);
		}
		
		return null;
	}

	/**
	 * Maps unexpected exceptions to their corresponding {@link IRequestHandler}.
	 * 
	 * @param e
	 * 			the current exception
	 * @param application
	 * 			the current application object
	 * @return the {@link IRequestHandler} for the current exception
	 */
	protected IRequestHandler mapUnexpectedExceptions(Exception e, final Application application)
	{
		final ExceptionSettings.UnexpectedExceptionDisplay unexpectedExceptionDisplay = application.getExceptionSettings()
			.getUnexpectedExceptionDisplay();

		logger.error("Unexpected error occurred", e);

		if (ExceptionSettings.SHOW_EXCEPTION_PAGE.equals(unexpectedExceptionDisplay))
		{
			Page currentPage = extractCurrentPage();
			return createPageRequestHandler(new PageProvider(new ExceptionErrorPage(e,
				currentPage)));
		}
		else if (ExceptionSettings.SHOW_INTERNAL_ERROR_PAGE.equals(unexpectedExceptionDisplay))
		{
			return createPageRequestHandler(new PageProvider(
				application.getApplicationSettings().getInternalErrorPage()));
		}
		
		// IExceptionSettings.SHOW_NO_EXCEPTION_PAGE
		return new ErrorCodeRequestHandler(500);
	}

	/**
	 * Creates a {@link RenderPageRequestHandler} for the target page provided by {@code pageProvider}.
	 * 
	 * Uses {@link RenderPageRequestHandler.RedirectPolicy#NEVER_REDIRECT} policy to preserve the original page's URL
	 * for non-Ajax requests and {@link RenderPageRequestHandler.RedirectPolicy#AUTO_REDIRECT} for AJAX requests.
	 * 
	 * @param pageProvider
	 * 			the page provider for the target page
	 * @return the request handler for the target page
	 */
	protected RenderPageRequestHandler createPageRequestHandler(PageProvider pageProvider)
	{
		RequestCycle requestCycle = RequestCycle.get();

		if (requestCycle == null)
		{
			throw new IllegalStateException(
				"there is no current request cycle attached to this thread");
		}

		RenderPageRequestHandler.RedirectPolicy redirect = RenderPageRequestHandler.RedirectPolicy.NEVER_REDIRECT;

		if (isProcessingAjaxRequest())
		{
			redirect = RenderPageRequestHandler.RedirectPolicy.AUTO_REDIRECT;
		}

		return new RenderPageRequestHandler(pageProvider, redirect);
	}
	
	/**
	 * @return true if current request is an AJAX request, false otherwise.
	 */
	protected boolean isProcessingAjaxRequest()
	{
		RequestCycle rc = RequestCycle.get();
		Request request = rc.getRequest();
		if (request instanceof WebRequest)
		{
			return ((WebRequest)request).isAjax();
		}
		return false;
	}

	/**
	 * @return the page being rendered when the exception was thrown, or {@code null} if it cannot
	 *         be extracted
	 */
	protected Page extractCurrentPage()
	{
		final RequestCycle requestCycle = RequestCycle.get();

		IRequestHandler handler = requestCycle.getActiveRequestHandler();

		if (handler == null)
		{
			handler = requestCycle.getRequestHandlerScheduledAfterCurrent();
		}

		if (handler instanceof IPageRequestHandler)
		{
			IPageRequestHandler pageRequestHandler = (IPageRequestHandler)handler;
			return (Page)pageRequestHandler.getPage();
		}
		return null;
	}
}