编码过滤器EncodingFilter

EncodingFilter.java

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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class EncodingFilter 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 servletRequest, ServletResponse servletResponse,
                          FilterChain chain) throws IOException,
         ServletException {
    	 HttpServletRequest request =(HttpServletRequest)servletRequest;
    	 HttpServletResponse response = (HttpServletResponse)servletResponse;
    	 
    	 // 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);
     }
}

web.xml

<filter>
	<filter-name>encodingfilter</filter-name>
         <!-- filter-class写EncodingFilter的路径 我这里是com.test.util.EncodingFilter -->
	<filter-class>com.test.util.EncodingFilter</filter-class>
	<init-param>
		<param-name>encoding</param-name>
		<param-value>GBK</param-value>		
	</init-param>
	<init-param>
		<param-name>ignore</param-name>
		<param-value>true</param-value>
	</init-param>	
</filter>
<filter-mapping>
	<filter-name>encodingfilter</filter-name>
	<url-pattern>/*</url-pattern>
</filter-mapping>