filter类的具体使用和配置

一。web.xml文件配置

xml 代码

<filter>
   <filter-name>Filter User</filter-name>
  <filter-class>cn.lingqi.filter.LogonFilter</filter-class>
  <init-param>
   <param-name>encoding</param-name>
   <param-value>gb2312</param-value>
  </init-param>
  </filter>
   <!-- filter-mapping>
 <filter-name>Set Character Encoding</filter-name>
 <url-pattern>/servlet/*</url-pattern>
  </filter-mapping-->
  <filter-mapping>
 <filter-name>Filter User</filter-name>
 <url-pattern>/cggl/list_vender.jsp</url-pattern>
  </filter-mapping>

二。filter类使用举例

java 代码

package cn.lingqi.filter;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
//用户登陆筛选器
public class LogonFilter implements Filter{
 protected FilterConfig filterConfig = null;
 protected String encoding = null;
 public void destroy() {
  // TODO Auto-generated method stub

 }

 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
  response.setContentType("text/html;charset=gb2312");
  PrintWriter out = response.getWriter();
  if ((request.getCharacterEncoding() == null)) {
            String encoding = selectEncoding(request);
            if (encoding != null)
                request.setCharacterEncoding(encoding);
        }
  out.println("<script>alert('test filter');</script>");
  chain.doFilter(request, response);

 }

 public void init(FilterConfig filterConfig) throws ServletException {
  this.filterConfig = filterConfig;
        this.encoding = filterConfig.getInitParameter("encoding");
 }

  protected String selectEncoding(ServletRequest request) {

         return (this.encoding);

     }
}