会话与过滤器

会话跟踪
  Cookie机制
   javax.sevlet.http.Cookie
   request.getCookie();
   response.addCookie();
   保存中文：
    Cookie cookie=new Cookie(URLEncoder.encode("姓名"，"UTF-8"),URLEncoder.encode("邓远奇","UTF-8"));
   保存二进制图片：
    File file=new File(image.path);
    byte [] binary=new bate[(int)file.lenth];
    InputStream in=this.getServletContext().getResourceAsStream(file.getName());
    in.read(binary);
    in.close;
    String content=BASE64Encoder.class.newInstance().encode(binary);
    Cookie cookie=new Cookie("file",content);
 
 过滤器Filter
  Filter:
   用户在servlet之外对request/response进行修改
   一个Filter必须实现javax.servlet.Filter接口，该接口有三个方法：
    public void init(FilterConfig config){};
    public void doFilter(Request request,Response response,FilterChain chain){};
     在doFilter（）方法中一定要执行chain.doFilter(request,response,chain);
    public void destory();
   Filter配置：
    在web.xml
     <filter>
      <filter-name></filter-name>
      <filter-class></filter-class>
      <init-param></init-param>
     </filter>
     <filter-mapping>
      <filter-name></filter-name>
      <url-pattern></url-pattern>
      <dispathcher>REQUEST/RESPONSE </dispathcher>  //配置到达servlet的方式
     </filter-mapping>
   字符编码过滤器：
    request.setCharacterEncoding("UTF-8");
    response.setCharacterEncoding("UTF-8");
   登陆过滤器：
    session.getAttribute("username");  //从session中取出username判断是否为null