请问在JB环境中filter用法简单例子：在线等！

Question

一个例子：
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;public class ChangeReqEncoding
    implements Filter {  protected FilterConfig config;
  protected String encoding;  public ChangeReqEncoding() {
  }  public void init(FilterConfig config) {
    this.config = config;
    encoding = config.getInitParameter("encoding");
    if (encoding == null) {
      encoding = "GBK";
    }
  }  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
      throws IOException, ServletException {
    HttpServletRequest srequest = (HttpServletRequest)request;
    srequest.setCharacterEncoding(encoding);
    chain.doFilter(request, response);
  }  public void destroy() {
  }
}web.xml里加上
<filter>
<filter-name>ChangeReqEncoding</filter-name>
<filter-class>com.icss.j2ee.servlet.filter.ChangeReqEncoding</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>GBK</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>ChangeReqEncoding</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>