ErrorPages.java

/*******************************************************************************
 * Copyright (c) 2012-2016 Codenvy, S.A.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   Codenvy, S.A. - initial API and implementation
 *******************************************************************************/
package org.everrest.core.tools;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import javax.servlet.ServletContext;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;

import static com.google.common.base.Throwables.propagate;
import static javax.xml.XMLConstants.FEATURE_SECURE_PROCESSING;

/**
 * Describes error-page references for web application in web.xml file.
 *
 * @author Max Shaposhnik
 */
public class ErrorPages {
    private static final Logger LOG = LoggerFactory.getLogger(ErrorPages.class);

    private final        Map<Integer, String> errorCodes     = new HashMap<>();
    private final        Map<String, String>  exceptionTypes = new HashMap<>();

    public ErrorPages(ServletContext servletContext) {
        loadErrorPages(servletContext, errorCodes, exceptionTypes);
    }

    public boolean hasErrorPage(int errorCode) {
        return errorCodes.get(errorCode) != null;
    }

    public boolean hasErrorPage(String exceptionType) {
        return exceptionTypes.get(exceptionType) != null;
    }

    public boolean hasErrorPage(Throwable exception) {
        return hasErrorPage(exception.getClass().getName());
    }

    protected void loadErrorPages(ServletContext servletContext, Map<Integer, String> errorCodes, Map<String, String> exceptionTypes) {
        InputStream input = servletContext.getResourceAsStream("/WEB-INF/web.xml");
        if (input != null) {
            try {
                DocumentBuilderFactory documentBuilderFactory = createFeaturedDocumentBuilderFactory();
                DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
                Document dom = documentBuilder.parse(input);
                XPathFactory xpathFactory = XPathFactory.newInstance();
                XPath xpath = xpathFactory.newXPath();
                NodeList all = (NodeList)xpath.evaluate("/web-app/error-page", dom, XPathConstants.NODESET);
                int length = all.getLength();
                for (int i = 0; i < length; i++) {
                    Node errorPage = all.item(i);
                    if (errorPage.getNodeType() == Node.ELEMENT_NODE) {
                        Element errorElement = (Element)errorPage;
                        NodeList locationList = errorElement.getElementsByTagName("location");
                        if (locationList.getLength() != 0) {
                            String location = locationList.item(0).getTextContent();
                            NodeList errorCodeList = errorElement.getElementsByTagName("error-code");
                            if (errorCodeList.getLength() != 0) {
                                try {
                                    Integer errorCode = Integer.valueOf(errorCodeList.item(0).getTextContent());
                                    errorCodes.put(errorCode, location);
                                } catch (NumberFormatException ignored) {
                                }
                            } else {
                                NodeList exceptionTypeList = errorElement.getElementsByTagName("exception-type");
                                if (exceptionTypeList.getLength() != 0) {
                                    exceptionTypes.put(exceptionTypeList.item(0).getTextContent(), location);
                                }
                            }
                        }
                    }
                }
            } catch (Exception e) {
                propagate(e);
            } finally {
                try {
                    input.close();
                } catch (IOException ignored) {
                }
            }
        }
    }

    private DocumentBuilderFactory createFeaturedDocumentBuilderFactory() {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        try {
            factory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
            factory.setFeature("http://xml.org/sax/features/external-general-entities", false);
            factory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
            factory.setFeature(FEATURE_SECURE_PROCESSING, true);
        } catch (ParserConfigurationException e) {
            LOG.debug(e.getMessage(), e);
        }
        return factory;
    }
}