1、Filter(重点)
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:
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(pom文件中)导包
<dependencies> <dependency> <groupId>javax.servlet</groupId> <artifactId>javax.servlet-api</artifactId> <version>3.1.0</version> </dependency> <dependency> <groupId>javax.servlet.jsp</groupId> <artifactId>javax.servlet.jsp-api</artifactId> <version>2.3.3</version> </dependency> <dependency> <groupId>javax.servlet.jsp.jstl</groupId> <artifactId>jstl-api</artifactId> <version>1.2</version> </dependency> <dependency> <groupId>taglibs</groupId> <artifactId>standard</artifactId> <version>1.1.2</version> </dependency> <!--连接数据库--> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.32</version> </dependency> </dependencies>
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编写过滤器(解决乱码用“resp.setContentType("text/html;charset=utf-8");”
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导包不要错
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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,就已经执行了,随时等待过滤对象) @Override 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); */ @Override 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); // 放行作用,让我们的请求继续走,如果不写,程序到这里就被拦截停止了! System.out.println("CharacterEncodingFilter执行后。。。"); } // 销毁(web服务器关闭的时候执行) @Override public void destroy() { System.out.println("CharacterEncodingFilter销毁"); } }
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在web.xml中配置
<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> 这样写,整个网站的请求都会走过滤器--> </filter-mapping>
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2、监听器
实现一个监听器的接口(有N种)
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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:看它的一举一动 // 一旦创建一个Session就会触发一次这个事件 @Override public void sessionCreated(HttpSessionEvent httpSessionEvent) { ServletContext servletContext = httpSessionEvent.getSession().getServletContext(); Integer onlineCount = (Integer) servletContext.getAttribute("OnlineCount"); System.out.println(httpSessionEvent.getSession().getId()); if (onlineCount == null){ onlineCount = new Integer(1); }else{ int count = onlineCount.intValue(); onlineCount = new Integer(count + 1); } servletContext.setAttribute("OnlineCount",onlineCount); } // 销毁Session监听 // 一旦销毁Session就会触发一次这个事件 @Override public void sessionDestroyed(HttpSessionEvent httpSessionEvent) { ServletContext servletContext = httpSessionEvent.getSession().getServletContext(); Integer onlineCount = (Integer) servletContext.getAttribute("OnlineCount"); if (onlineCount == null){ onlineCount = new Integer(0); }else{ int count = onlineCount.intValue(); onlineCount = new Integer(count - 1); } servletContext.setAttribute("OnlineCount",onlineCount); } }
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web.xml中注册监听器
<!-- 注册监听器 --> <listener> <listener-class>com.kuang.listener.OnlineCountListener</listener-class> </listener>
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看情况是否使用!