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*** THIS IS AN OBSOLETE VERSION UPLOADED FOR USE WITH CEDAR-COMMON.*** The Server Library for GWT is a collection of Java server side components for the Google Web Toolkit AJAX framework with the focus on the Spring framework by facilitating publishing of Spring beans as RPC services with support for Hibernate-managed entities.

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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 worthreading
 * article 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);
	}

	@SuppressWarnings("unchecked")
	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 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++;
		}
	}
}