Filter过滤器

  • Filter:过滤器,用来过滤网站的数据(处理中文乱码,登录验证…)

  • Filter开发步骤

    • 导包配置maven
    • 编写过滤器(导包:javax.servlet.Filter)
    public class CharacterEncodingFilter implements Filter {
    
        //初始化
        public void init(FilterConfig filterConfig) throws ServletException {
            System.out.println("CharacterEncodingFilter已经初始化");
        }
    
        //chain:链
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
            request.setCharacterEncoding("utf-8");
            response.setCharacterEncoding("utf-8");
            response.setContentType("text/html;charset=utf-8");
    
            System.out.println("CharacterEncodingFilter执行前");
            chain.doFilter(request,response); //让请求继续走,如果不写程序到这里自动停止
            System.out.println("CharacterEncodingFilter执行后");
        }
    
        //销毁:web服务器关闭时,过滤器会被销毁
        public void destroy() {
            System.out.println("CharacterEncodingFilter已经销毁");
        }
    }
    
    • web.xml配置过滤器
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.java.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <!--过滤/servlet路径下的所有请求-->
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>
    
  • 总结:

    1. 过滤器中所有的代码,在过滤特定请求的时候都会执行
    2. 必须要让过滤器继续通行
    3. chain.doFilter(request,response);必须写

案例:用户登录之后才能进入主页,用户注销之后则不能进入

  • 分析
    • 1.用户登录之后向Session中放入用户数据信息
    • 2.进入主页的时候要判断用户是否已经登录(过滤器)

登录

public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取前端请求的参数
        String username = req.getParameter("username");

        if (username.equals("admin")){ //登录成功
            req.getSession().setAttribute(Constant.USER_SESSION,req.getSession().getId());
            resp.sendRedirect("/sys/success.jsp");
        }else { //登录失败
            resp.sendRedirect("/error.jsp");
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

登出

public class LogoutServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String user_session = (String) req.getSession().getAttribute(Constant.USER_SESSION);
        if (user_session != null){
            req.getSession().removeAttribute(Constant.USER_SESSION);
            resp.sendRedirect("/login.jsp");
        }else {
            resp.sendRedirect("/login.jsp");
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

过滤器

public class SysFilter implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;

        if (request.getSession().getAttribute(Constant.USER_SESSION)==null) {

            response.sendRedirect("/error.jsp");
        }
        filterChain.doFilter(servletRequest,servletResponse);
    }

    public void destroy() {

    }
}

提取常量工具类

public class Constant {
    public final static String USER_SESSION = "USER_SESSION";
}
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