org.gwtwidgets.server.filters.ResponseHeaderFilter.java Source code

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Here is the source code for org.gwtwidgets.server.filters.ResponseHeaderFilter.java

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/*
 * 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
 * 
 * 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.gwtwidgets.server.filters;

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

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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

/**
 * Servlet Filter that applies any HTTP header to a matched URL. Init parameters
 * are HTTP header-value pairs. Will silently fail when the ServletResponse does
 * not cast to a {@link HttpServletResponse}. A special init-parameter is
 * 'ResponseHeaderFilter.UrlPattern': it is not set as an HTTP header but is
 * rather a regular expression which can be used to further refine URLs on which
 * the filter should match. Headers containing an empty value are removed from
 * the response, even if they already exist there.
 * 
 * Inspired by a very <a
 * href="http://www.onjava.com/pub/a/onjava/2004/03/03/filters.html">worthreading
 * article</a> from Jayson Falkner.
 * 
 * @author George Georgovassilis, g.georgovassilis[at]gmail.com
 * 
 */
public class ResponseHeaderFilter implements Filter {

    public final static String URL_PATTERN = "ResponseHeaderFilter.UrlPattern";

    private String[] headers = new String[0];

    private String[] values = new String[0];

    private Log logger = LogFactory.getLog(getClass());

    private Pattern urlPattern = Pattern.compile(".*?");

    private void setupMatcher(String pattern) {
        urlPattern = Pattern.compile(pattern);
        logger.debug("Matching " + pattern);
    }

    private void addHeaders(HttpServletRequest request, HttpServletResponse response) {
        response.setBufferSize(0);
        String query = request.getRequestURI();
        Matcher urlMatcher = urlPattern.matcher(query);
        if (!urlMatcher.matches())
            return;
        for (int i = 0; i < headers.length; i++)
            response.setHeader(headers[i], values[i]);
    }

    private int getSize(Enumeration<?> e) {
        int size = 0;
        for (; e.hasMoreElements(); e.nextElement(), size++)
            ;
        return size;
    }

    public void destroy() {
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        if (response instanceof HttpServletResponse)
            addHeaders((HttpServletRequest) request, (HttpServletResponse) response);
        chain.doFilter(request, response);
    }

    public void init(FilterConfig conf) throws ServletException {
        int size = getSize(conf.getInitParameterNames());
        if (conf.getInitParameter(URL_PATTERN) != null) {
            size--;
            setupMatcher(conf.getInitParameter(URL_PATTERN));
        }
        headers = new String[size];
        values = new String[size];
        if (size == 0) {
            logger.warn("Instantiated ResponseHeaderFilter without header mappings");
            return;
        }
        logger.debug("ResponseHeaderFilter header mappings:");
        Enumeration<String> e = conf.getInitParameterNames();
        for (int i = 0; i < size;) {
            String header = e.nextElement().toString();
            if (URL_PATTERN.equals(header))
                continue;
            headers[i] = header;
            values[i] = conf.getInitParameter(headers[i]);
            if ("".equals(values[i]))
                values[i] = null;
            logger.debug(headers[i] + " = " + values[i]);
            i++;
        }
    }
}