javax.servlet.Filter 的应用

 

Filter过滤器的使用本篇文章是介绍javax.servlet包中Filter的几个功能,一是字符编码过滤,二是拦截指文件夹中的文件,实现登录验证.实现以上两个功能需以下几个步骤:1、实现javax.servlet.Filter接口，编写两个类，如下： /** * 作用：过滤编码 */package filter;import java.io.IOException;import javax.servlet.*;import javax.servlet.http.HttpServletRequest;public class EncodingFilter implements Filter{    protected FilterConfig filterConfig;    private String targetEncoding;    public EncodingFilter()    {        targetEncoding = "gb2312";//直接初始化0912    }    public void init(FilterConfig filterconfig) throws ServletException    {        filterConfig = filterconfig;        //targetEncoding = filterconfig.getInitParameter("encoding");//web.xml挂参初始化    }    public void doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain)        throws IOException, ServletException    {        HttpServletRequest httpservletrequest = (HttpServletRequest)servletrequest;        httpservletrequest.setCharacterEncoding(targetEncoding);        System.out.println("使用" targetEncoding "对请求进行编码过滤");        filterchain.doFilter(servletrequest, servletresponse);    }    public void setFilterConfig(FilterConfig filterconfig)    {        filterConfig = filterconfig;    }    public void destroy()    {        filterConfig = null;    }} /** * 作用：过滤外界非法的进入页面 * 注意：使用该功能时，一定要把登录页与被过滤文件夹设为同级，否则会出现循环 */package filter;import java.io.IOException;import javax.servlet.*;import javax.servlet.http.*;public class ManageFilter implements Filter{    String LOGIN_PAGE;    protected FilterConfig filterConfig;    public ManageFilter()    {        LOGIN_PAGE = "/login.jsp";    }    public void doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain)        throws IOException, ServletException    {        HttpServletRequest request = (HttpServletRequest) servletrequest;        HttpServletResponse response = (HttpServletResponse) servletresponse;        HttpSession session = request.getSession();        String key = "";        try        {            //通过验证时在session中存的一个标志     key = (String) session.getAttribute("key");                                   if (key!= null&&key.equals("ok"))            {                               filterchain.doFilter(servletrequest, servletresponse);            }            else            {                response.sendRedirect(LOGIN_PAGE);                System.out.println("被拦截一个未认证的请求");            }        }        catch (Exception exception)        {            exception.printStackTrace();        }    }    public void setFilterConfig(FilterConfig filterconfig)    {        filterConfig = filterconfig;    }    public void destroy()    {        filterConfig = null;    }    public void init(FilterConfig filterconfig)        throws ServletException    {        filterConfig = filterconfig;    }} 2、在web.xml中做一些设置       code     filter.EncodingFilter         manage     filter.ManageFilter        code     /*         manage     <!-- <url-pattern>/ShuiBaoRHPWK_NEW/system/ruhepaiwukou/*</url-pattern>-->     /servlets-examples/*