11、Filter（重点）
Filter：过滤器，用来过滤网站的数据；
- 处理中文乱码
- 登陆验证...
Filter开发步骤：
- 导包
- 编写过滤器
- 导包不要错
b. 实现Filter接口，重写对应的方法即可
public class CharacterEncodingFilter implements Filter { //初始化：web服务器启动，就已经初始化了，随时等待过滤对象出现！ public void init(FilterConfig filterConfig) throws ServletException { System.out.println("CharacterEncodingFilter初始化"); } //Chain : 链 /* 1. 过滤器中的所有代码，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 filterChain.doFilter(servletRequest,servletResponse); */ public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { servletRequest.setCharacterEncoding("utf-8"); servletResponse.setCharacterEncoding("utf-8"); servletResponse.setContentType("text/html;charset=UTF-8"); System.out.println("CharacterEncodingFilter执行前..."); filterChain.doFilter(servletRequest,servletResponse); //让我们的请求继续走，如果不写，程序到这里就被拦截停止！ System.out.println("CharacterEncodingFilter执行后..."); } //销毁：web服务器关闭的时候，过滤器会销毁 public void destroy() { System.out.println("CharacterEncodingFilter销毁"); } }
c. 在web.xml中配置 Filter
<servlet> <servlet-name>ShowServlet</servlet-name> <servlet-class>com.kuang.servlet.ShowServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>ShowServlet</servlet-name> <url-pattern>/servlet/show</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>ShowServlet</servlet-name> <url-pattern>/show</url-pattern> </servlet-mapping> <filter> <filter-name>CharacterEncodingFilter</filter-name> <filter-class>com.kuang.filter.CharacterEncodingFilter</filter-class> </filter> <filter-mapping> <filter-name>CharacterEncodingFilter</filter-name> <!--只要是 /servlet的任何请求，都会经过这个过滤器--> <url-pattern>/servlet/*</url-pattern> <!--<url-pattern>/*</url-pattern>--> </filter-mapping>
12、监听器
实现一个监听器的接口； （有N中）
- 编写一个监听器
实现监听器的接口...
//统计网站在线人数 ： 统计session public class OnlineCountListener implements HttpSessionListener { //创建session监听：看你的一举一动 //一旦创建一个session就会触发一次这个事件！ public void sessionCreated(HttpSessionEvent httpSessionEvent) { ServletContext context = httpSessionEvent.getSession().getServletContext(); System.out.println(httpSessionEvent.getSession().getId()); Integer onlineCount = (Integer) context.getAttribute("OnlineCount"); if (onlineCount==null){ onlineCount = new Integer(1); }else { int count = onlineCount.intValue(); onlineCount = new Integer(count+1); } context.setAttribute("OnlineCount",onlineCount); } //销毁session监听 //一旦销毁session就会触发一次这个事件！ public void sessionDestroyed(HttpSessionEvent httpSessionEvent) { ServletContext context = httpSessionEvent.getSession().getServletContext(); Integer onlineCount = (Integer) context.getAttribute("OnlineCount"); if (onlineCount==null){ onlineCount = new Integer(0); }else { int count = onlineCount.intValue(); onlineCount = new Integer(count-1); } context.setAttribute("OnlineCount",onlineCount); } /* Session销毁： 1. 手动销毁 getSession.invalidate() 2. 自动销毁 在web.xml中设置session过期时间 */ }
- web.xml中注册监听器
<!--注册监听器--> <listener> <listener-class>com.kuang.listener.OnlineCountListener</listener-class> </listener>
- 看情况是否使用！
13、过滤器、监听器常见应用
监听器：GUI编程中经常使用；
public class TestPanel1 { public static void main(String[] args) { Frame frame = new Frame("中秋节快乐"); //新建一个窗体 Panel panel = new Panel(null); //面板 frame.setLayout(null); //设置窗体的布局 frame.setBounds(50,50,300,300); frame.setBackground(Color.blue); //设置背景颜色 panel.setBounds(70,70,70,70); //设置背景颜色 panel.setBackground(Color.GREEN); frame.add(panel); frame.setVisible(true); //监听事件，监听关闭事件，使用适配器 frame.addWindowListener(new WindowAdapter() { @Override public void windowClosing(WindowEvent e) { System.exit(0); } }); } }
实现：用户登录之后才能进入主页！用户注销后就不能进入主页了！
- 用户登陆之后，向Session中放入用户的数据
- 进入主页的时候要判断用户是否已经登录；要求：在过滤器中实现！
//ServletRequest HttpServletRequest HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest; HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse; if (httpServletRequest.getSession().getAttribute(Constant.USER_SESSION)==null){ httpServletResponse.sendRedirect("/error.jsp"); } filterChain.doFilter(servletRequest, servletResponse);
项目全部代码：
public class Constant { public final static String USER_SESSION = "USER_SESSION"; } ============================================================= 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")){ //登陆成功 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); } } ========================================================================== public class LogoutServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { Object user_session = 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); } } =============================================================================== public class SysFilter implements Filter { public void init(FilterConfig filterConfig) throws ServletException { } public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { /* 实现会员分级： if (req.getSession().setAttribute(Constant.USER_SESSION).level==VIP1){ response.sendRedirect("/vip1/index.jsp"); } if (req.getSession().setAttribute(Constant.USER_SESSION).level==VIP2){ response.sendRedirect("/vip2/index.jsp"); } if (req.getSession().setAttribute(Constant.USER_SESSION).level==VIP3){ response.sendRedirect("/vip3/index.jsp"); } */ //ServletRequest HttpServletRequest HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest; HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse; if (httpServletRequest.getSession().getAttribute(Constant.USER_SESSION)==null){ httpServletResponse.sendRedirect("/error.jsp"); } filterChain.doFilter(servletRequest, servletResponse); } public void destroy() { } }
<%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <h1>错误</h1> <h3>没有权限，用户名错误</h3> <p><a href="/Login.jsp">返回登录页面</a></p> </body> </html> ==================================================================== <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <h1>主页</h1> <p><a href="/servlet/logout">注销</a></p> </body> </html> ======================================================================= <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <h1>登录</h1> <form action="/servlet/login" method="post"> 用户名：<input type="text" name="username"><br> <input type="submit"> </form> </body> </html> ======================================================================== <?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0"> <servlet> <servlet-name>LoginServlet</servlet-name> <servlet-class>com.kuang.servlet.LoginServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>LoginServlet</servlet-name> <url-pattern>/servlet/login</url-pattern> </servlet-mapping> <servlet> <servlet-name>LogoutServlet</servlet-name> <servlet-class>com.kuang.servlet.LogoutServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>LogoutServlet</servlet-name> <url-pattern>/servlet/logout</url-pattern> </servlet-mapping> <filter> <filter-name>SysFilter</filter-name> <filter-class>com.kuang.servlet.SysFilter</filter-class> </filter> <filter-mapping> <filter-name>SysFilter</filter-name> <url-pattern>/sys/*</url-pattern> </filter-mapping> </web-app>
