net.sourceforge.vulcan.web.ContentTypeFilter.java Source code

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Here is the source code for net.sourceforge.vulcan.web.ContentTypeFilter.java

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/*
 * Vulcan Build Manager
 * Copyright (C) 2005-2012 Chris Eldredge
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
package net.sourceforge.vulcan.web;

import java.io.IOException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.lang.StringUtils;
import org.springframework.web.filter.OncePerRequestFilter;

/**
 * J2EE Filter which uses decorator pattern and some custom rules to decide which
 * Content-type header should be sent to a User-Agent (browser).  Specifically, this
 * filter is intended to set the Content-type to "application/xhtml+xml" in most cases.
 * However, if the User-Agent is known to misbehave when such a Content-type is set,
 * the filter will fall back to "text/html".
 * <br><br>
 * Implementation details turn out to complicate things.  In Tomcat 5.5, the default
 * Content-type for a JSP Document is "text/xml", but in WebLogic 9 the default is
 * "text/html".  Therefore, a "suppressContentTypes" init-param is provided to 
 * configure a comma-delimited list of Content-types which should not be allowed
 * to override the Content-type chosen by this filter.
 * <br><br>
 * If a Servlet (JSP or other) sets the Content-type to something that is not found in
 * the "supressContentTypes" list, the Content-type will be overridden to use that value.
 * This allows special cases (such as "application/xml+rss") to override this filter.
 */
public class ContentTypeFilter extends OncePerRequestFilter {
    public static final String HEADER_USER_AGENT = "User-Agent";

    public static final String PARAM_DEFAULT_CONTENT_TYPE = "defaultContentType";
    public static final String PARAM_LEGACY_CONTENT_TYPE = "legacyContentType";
    public static final String PARAM_SUPPRESS_CONTENT_TYPES = "suppressContentTypes";
    public static final String PARAM_DETECT_BROWSER = "detectBrowser";

    static final String ATTR_DISABLE_SUPPRESSION = ContentTypeFilter.class.getName() + ":DisableSuppression";

    private static final Pattern userAgentRegex = Pattern.compile(".*MSIE ([\\d]*).*");

    private String defaultContentType;
    private String legacyContentType;
    private String[] suppressContentTypes;
    private boolean detectBrowser;

    public ContentTypeFilter() {
        addRequiredProperty(PARAM_DEFAULT_CONTENT_TYPE);
    }

    public void setDefaultContentType(String defaultContentType) {
        this.defaultContentType = defaultContentType;
    }

    public void setLegacyContentType(String legacyContentType) {
        this.legacyContentType = legacyContentType;
    }

    public void setSuppressContentTypes(String suppressContentType) {
        this.suppressContentTypes = suppressContentType.split(",");
    }

    public boolean isDetectBrowser() {
        return detectBrowser;
    }

    public void setDetectBrowser(boolean detectBrowser) {
        this.detectBrowser = detectBrowser;
    }

    public static void disableContentTypeSupression(ServletRequest request) {
        request.setAttribute(ATTR_DISABLE_SUPPRESSION, Boolean.TRUE);
    }

    public static boolean isContentTypeSupressionEnabled(ServletRequest request) {
        Boolean value = (Boolean) request.getAttribute(ATTR_DISABLE_SUPPRESSION);
        return value == null || Boolean.FALSE.equals(value);
    }

    @Override
    protected void initFilterBean() throws ServletException {
        if (detectBrowser && legacyContentType == null) {
            throw new ServletException("You must specify " + PARAM_LEGACY_CONTENT_TYPE + " in web.xml when using "
                    + PARAM_DETECT_BROWSER);
        }
        if (suppressContentTypes != null) {
            for (int i = 0; i < suppressContentTypes.length; i++) {
                suppressContentTypes[i] = suppressContentTypes[i].trim();
            }
        } else {
            suppressContentTypes = new String[0];
        }
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain)
            throws ServletException, IOException {

        final String contentType = detectContentType(request);

        final HttpServletResponseContentTypeWrapper responseWrapper = new HttpServletResponseContentTypeWrapper(
                request, response, suppressContentTypes, contentType);

        response.addHeader("Cache-Control", "max-age=0");

        chain.doFilter(request, responseWrapper);
    }

    private String detectContentType(HttpServletRequest request) {
        final String userAgent = request.getHeader(HEADER_USER_AGENT);

        if (!StringUtils.isBlank(userAgent)) {
            final Matcher matcher = userAgentRegex.matcher(userAgent);

            if (matcher.matches()) {
                request.setAttribute(Keys.BROWSER_IE, Boolean.TRUE);
                return legacyContentType;
            }
        }

        return defaultContentType;
    }
}