過濾器
Filter:過濾器 ,用來過濾網站的數據;
- 處理中文亂碼
- 登錄驗證….
1.導包:過濾器要到的包是 javax.servlet
2.編寫過濾器:實現Filter接口,重寫對應的方法即可
public class CharacterEncodingFilter implements Filter {
//初始化:web服務器啓動,就以及初始化了,隨時等待過濾對象出現!
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("CharacterEncodingFilter初始化");
}
//Chain : 鏈
/*
1. 過濾中的所有代碼,在過濾特定請求的時候都會執行
2. 必須要讓過濾器繼續同行
chain.doFilter(request,response);
*/
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執行前....");
chain.doFilter(request,response); //讓我們的請求繼續走,如果不寫,程序到這裏就被攔截停止!
System.out.println("CharacterEncodingFilter執行後....");
}
//銷燬:web服務器關閉的時候,過濾會銷燬
public void destroy() {
System.out.println("CharacterEncodingFilter銷燬");
}
}
3.在web.xml中配置Filter
<filter>
<filter-name>CharacterEncodingFilter</filter-name>
<filter-class>com.yang.servlet.CharacterEncodingFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>CharacterEncodingFilter</filter-name>
<!--只要是 /servlet的任何請求,會經過這個過濾器-->
<url-pattern>/zifu</url-pattern>
</filter-mapping>
監聽器
實現監聽器的接口
public class OnlineCountListener implements HttpSessionListener {
//創建session監聽: 看你的一舉一動
//一旦創建Session就會觸發一次這個事件!
public void sessionCreated(HttpSessionEvent se) {
ServletContext ctx = se.getSession().getServletContext();
System.out.println(se.getSession().getId());
Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");
if (onlineCount==null){
onlineCount = new Integer(1);
}else {
int count = onlineCount.intValue();
onlineCount = new Integer(count+1);
}
ctx.setAttribute("OnlineCount",onlineCount);
}
//銷燬session監聽
//一旦銷燬Session就會觸發一次這個事件!
public void sessionDestroyed(HttpSessionEvent se) {
ServletContext ctx = se.getSession().getServletContext();
Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");
if (onlineCount==null){
onlineCount = new Integer(0);
}else {
int count = onlineCount.intValue();
onlineCount = new Integer(count-1);
}
ctx.setAttribute("OnlineCount",onlineCount);
}
}
編寫測試,用index.jsp即可
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>登錄</title>
</head>
<body>
<h1>當前:<span><%=this.getServletConfig().getServletContext().getAttribute("OnlineCount")%>人在使用</span></h1>
</html>
在web.xml註冊監聽器
<!--註冊監聽器-->
<listener>
<listener-class>com.yang.servlet.OnlineCountListener</listener-class>
</listener>
應用
public class TestPanel {
public static void main(String[] args) {
Frame frame = new Frame("中秋節快樂"); //新建一個窗體
Panel panel = new Panel(null); //面板
frame.setLayout(null); //設置窗體的佈局
frame.setBounds(300, 300, 500, 500);
frame.setBackground(new Color(0, 0, 255)); //設置背景顏色
panel.setBounds(50, 50, 300, 300);
panel.setBackground(new Color(0, 255, 0)); //設置背景顏色
frame.add(panel);
frame.setVisible(true);
//監聽事件,監聽關閉事件
frame.addWindowListener(new WindowAdapter() {
@Override
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
}
}