package com.jspdev.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

/**
 * <p>
 * Example filter that sets the character encoding to be used in parsing the
 * incoming request, either unconditionally or only if the client did not
 * specify a character encoding. Configuration of this filter is based on the
 * following initialization parameters:
 * </p>
 * <ul>
 * <li><strong>encoding</strong> - The character encoding to be configured for
 * this request, either conditionally or unconditionally based on the
 * <code>ignore</code> initialization parameter. This parameter is required,
 * so there is no default.</li>
 * <li><strong>ignore</strong> - If set to "true", any character encoding
 * specified by the client is ignored, and the value returned by the
 * <code>selectEncoding()</code> method is set. If set to "false,
 * <code>selectEncoding()</code> is called <strong>only</strong> if the
 * client has not already specified an encoding. By default, this parameter is
 * set to "true".</li>
 * </ul>
 * 
 * <p>
 * Although this filter can be used unchanged, it is also easy to subclass it
 * and make the <code>selectEncoding()</code> method more intelligent about
 * what encoding to choose, based on characteristics of the incoming request
 * (such as the values of the <code>Accept-Language</code> and
 * <code>User-Agent</code> headers, or a value stashed in the current user's
 * session.
 * </p>
 * 
 * @author Craig McClanahan
 * @version $Revision: 1.2 $ $Date: 2006/03/21 09:37:07 $
 */

public class CharacterEncodingFilter implements Filter {

	// ----------------------------------------------------- Instance Variables

	/**
	 * The default character encoding to set for requests that pass through this
	 * filter.
	 */
	protected String encoding = null;

	/**
	 * The filter configuration object we are associated with. If this value is
	 * null, this filter instance is not currently configured.
	 */
	protected FilterConfig filterConfig = null;

	/**
	 * Should a character encoding specified by the client be ignored?
	 */
	protected boolean ignore = true;

	// --------------------------------------------------------- Public Methods

	/**
	 * Take this filter out of service.
	 */
	public void destroy() {

		this.encoding = null;
		this.filterConfig = null;

	}

	/**
	 * Select and set (if specified) the character encoding to be used to
	 * interpret request parameters for this request.
	 * 
	 * @param request
	 *            The servlet request we are processing
	 * @param result
	 *            The servlet response we are creating
	 * @param chain
	 *            The filter chain we are processing
	 * 
	 * @exception IOException
	 *                if an input/output error occurs
	 * @exception ServletException
	 *                if a servlet error occurs
	 */
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {

		// Conditionally select and set the character encoding to be used
		if (ignore || (request.getCharacterEncoding() == null)) {
			String encoding = selectEncoding(request);
			if (encoding != null) {
				request.setCharacterEncoding(encoding);
				response.setContentType("text/html; charset=" + encoding);
			}
		}

		// Pass control on to the next filter
		chain.doFilter(request, response);

	}

	/**
	 * Place this filter into service.
	 * 
	 * @param filterConfig
	 *            The filter configuration object
	 */
	public void init(FilterConfig filterConfig) throws ServletException {

		this.filterConfig = filterConfig;
		this.encoding = filterConfig.getInitParameter("encoding");
		String value = filterConfig.getInitParameter("ignore");
		if (value == null)
			this.ignore = true;
		else if (value.equalsIgnoreCase("true"))
			this.ignore = true;
		else if (value.equalsIgnoreCase("yes"))
			this.ignore = true;
		else
			this.ignore = false;

	}

	// ------------------------------------------------------ Protected Methods

	/**
	 * Select an appropriate character encoding to be used, based on the
	 * characteristics of the current request and/or filter initialization
	 * parameters. If no character encoding should be set, return
	 * <code>null</code>.
	 * <p>
	 * The default implementation unconditionally returns the value configured
	 * by the <strong>encoding</strong> initialization parameter for this
	 * filter.
	 * 
	 * @param request
	 *            The servlet request we are processing
	 */
	protected String selectEncoding(ServletRequest request) {

		return (this.encoding);

	}

}