setcharacterencodingfilter.java

java shh架构的例程 对初学者有较好的指导作用

/*
 * 创建日期 2005-7-5
 *
 */
package com.ibm.sample.web.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;

public class SetCharacterEncodingFilter 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);
		}

	// 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);

	}

}//EOC