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滁州公司做网站,网站建设图片按钮,dedecms 购物网站,asp.net 网站开发视频过滤器（filter） 将浏览器请求的数据进行过滤，对于服务器向浏览器的相应进行过滤 //TODO:当访问/servlet1时，会先经过MyFilter1过滤器，再经过MyServlet1 WebFilter("/servlet1") public class MyFilter1 imp…

过滤器（filter）

将浏览器请求的数据进行过滤，对于服务器向浏览器的相应进行过滤

//TODO:当访问/servlet1时，会先经过MyFilter1过滤器，再经过MyServlet1
@WebFilter("/servlet1")
public class MyFilter1 implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("MyFilter1过滤器执行了");// 放行，继续执行下一个过滤器或目标资源filterChain.doFilter(servletRequest,servletResponse);}
}

Filter的生命周期：

初始化方法（init）：

Filter的创建和销毁由Web服务器负责（Tomcat）

拦截请求方法（doFilter）：

当浏览器客户端访问与过滤器有关联的URL的时候，Servlet过滤器会先执行doFilter方法，在通过FilterChain参数去访问后续的过滤器或者直接访问对应的资源

销毁方法（destroy):

Filter对象在创建了之后会驻留在内存中，当Web应用移除的时候或者服务器停止的时候才会销毁，在Web容器卸载Filter对象之前被调用，用于释放过滤器使用的资源。

@WebFilter("/servlet1")
public class MyFilter2 implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {System.out.println("MyFilter2过滤器初始化");}@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("MyFilter2过滤器执行了");// 放行，继续执行下一个过滤器或目标资源filterChain.doFilter(servletRequest,servletResponse);}//关闭Tomcat的时候会执行该方法@Overridepublic void destroy() {System.out.println("MyFilter2过滤器销毁");}
}

过滤器实现设置字符编码

//过滤器实现设置字符编码
@WebFilter("/servlet2")
public class MyFilter3 implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {// TODO:设置为utf-8编码HttpServletRequest request = (HttpServletRequest) servletRequest;request.setCharacterEncoding("UTF-8");filterChain.doFilter(servletRequest,servletResponse);}
}

通过Filter实现页面总的统计量PV：通过Ctrl+shift+delete去进行清除缓存

//TODO:通过Filter实现统计页面总的访问量PV
@WebFilter("/*")
public class MyFilter4 implements Filter {private final static String PV_COUNT = "pvCount";@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) servletRequest;HttpServletResponse response = (HttpServletResponse) servletResponse;ServletContext application = request.getServletContext();Integer count = (Integer)application.getAttribute(PV_COUNT);if (count == null){//第一次访问application.setAttribute(PV_COUNT,1);}else {//不是第一次访问int count1 = count;application.setAttribute(PV_COUNT,count1+1);}System.out.println("当前的页面访问量为："+ application.getAttribute(PV_COUNT));filterChain.doFilter(servletRequest,servletResponse);}
}

监听器（Listener）

在Javaweb中用于监听Servlet的三个作用域的程序就是监听器，Javaweb的Servlet作用域对象：ServletContext/HttpSession/HttpServletRequest三个对象

（应用程序/会话/请求）—》三个对象

监听器的基础：

监听生命周期的变化：

ServletContextListener：监听ServletContext生命周期

HttpSessionListener：监听HttpSession生命周期

HttpServletRequestListener：监听HttpServletRequest生命周期

监听属性变化：（setAttribute，getAttribute，removeAttribute）

ServletContextAttributeListener：监听ServletContext属性变化

HttpSessionAttributeListener：监听HttpSessionListener属性变化

HttpServletRequestAttributeListener：监听HttpServletRequest属性变化

Request域的监听器：–一次请求的时间是很短的

两个监听器的接口

ServletRequestListener：生命周期监听

ServletRequestAttributeListener：属性监听

@WebListener
public class RequestListener implements ServletRequestListener, ServletRequestAttributeListener {// 请求初始化监听public void requestInitialized(javax.servlet.ServletRequestEvent servletRequestEvent) {System.out.println("请求初始化");}// 请求销毁监听public void requestDestroyed(javax.servlet.ServletRequestEvent servletRequestEvent) {System.out.println("请求销毁");}// 请求属性添加监听public void attributeAdded(javax.servlet.ServletRequestAttributeEvent servletRequestAttributeEvent) {System.out.println("添加属性");}// 请求属性删除监听public void attributeRemoved(javax.servlet.ServletRequestAttributeEvent servletRequestAttributeEvent) {System.out.println("删除属性");}// 请求属性替换监听public void attributeReplaced(javax.servlet.ServletRequestAttributeEvent servletRequestAttributeEvent) {System.out.println("替换属性");}
}

Session域的监听器：

两个监听器的接口

HttpSessionListener：生命周期监听

HttpSessionAttributeListener：属性监听

@WebListener
public class SessionListener implements HttpSessionListener, HttpSessionAttributeListener {@Overridepublic void attributeAdded(HttpSessionBindingEvent event) {System.out.println("SessionListener监听到属性添加了");}@Overridepublic void attributeRemoved(HttpSessionBindingEvent event) {System.out.println("SessionListener监听到属性删除了");}@Overridepublic void attributeReplaced(HttpSessionBindingEvent event) {System.out.println("SessionListener监听到属性替换了");}@Overridepublic void sessionCreated(HttpSessionEvent se) {System.out.println("SessionListener监听到session创建了");}@Overridepublic void sessionDestroyed(HttpSessionEvent se) {System.out.println("SessionListener监听到session销毁了");}
}

ServletContext域的监听器：

两个监听器的接口

ServletContextListener：生命周期监听—Tomcat一启动就监听

ServletContextAttributeListener：属性监听

public class ContextListener implements ServletContextListener, ServletContextAttributeListener {@Overridepublic void attributeAdded(ServletContextAttributeEvent event) {System.out.println("ServletContextAttributeListener监听器监听到ServletContext的属性被添加了");}@Overridepublic void contextDestroyed(ServletContextEvent sce) {System.out.println("ServletContextListener监听器监听到ServletContext被销毁了");}@Overridepublic void contextInitialized(ServletContextEvent sce) {System.out.println("ServletContextListener监听器监听到ServletContext被创建了");}@Overridepublic void attributeReplaced(ServletContextAttributeEvent event) {System.out.println("ServletContextAttributeListener监听器监听到ServletContext的属性被替换了");}@Overridepublic void attributeRemoved(ServletContextAttributeEvent event) {System.out.println("ServletContextAttributeListener监听器监听到ServletContext的属性被移除了");}
}