过滤器
- 在 Java 后端开发中，过滤器（Filter）是一种用于拦截请求和响应的组件，可以用于对请求进行预处理、对响应进行后处理，以及实现请求和响应的过滤和转换等操作。通常情况下，过滤器用于在请求到达 Servlet 之前或响应被发送到客户端之前，对请求或响应进行某些操作。如字符编码过滤器、登录验证过滤器、权限控制过滤器、异常处理过滤器。
- 拦截器的拦截顺序为拦截器类名的自然排序
package priv.noby.filter.filter;
import javax.servlet.*;
import javax.servlet.annotation.*;
import java.io.IOException;
@WebFilter(filterName = "FilterNoteFilter",value = {"/a.jsp","/filterdir/*","/dServlet","*.html"})
public class FilterNoteFilter implements Filter {
public void init(FilterConfig config){
System.out.println("FilterInit");
}
public void destroy() {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
System.out.println("放行前一般处理request数据...");
chain.doFilter(request, response);
System.out.println("放行后一般处理response数据...");
}
}
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>
<html>
<head>
<title>a</title>
</head>
<body>
ajsp
<%
System.out.println("访问a.jsp资源...");
%>
</body>
</html>
监听器
- 在 Java 后端开发中，监听器（Listener）是一种用于监听 Web 应用程序中的事件的组件。通过监听器，我们可以在 Web 应用程序的生命周期中，捕获和处理各种事件。监听器通常用于实现某些特定功能或提供一些服务，例如：在 Web 应用程序启动时加载某些资源或初始化一些参数、在 Session 创建时保存用户登录信息、在 ServletContext 销毁时释放资源等等。监听器可以在 Web 应用程序的 Web.xml 文件中进行配置，可以在多个 Servlet 或 JSP 之间共享，也可以通过注解方式进行配置。
- 分类
- ServletContextListener 用于对 ServletContexti 对象进行监听（创建、销毁）
- ServletContextAttributeListener 对 ServletContexti 对象中属性的监听（增删改属性）
- HttpSessionListener 对 Session 对象的整体状态的监听（创建、销毁）
- HttpSessionAttributeListener 对 Session 对象中的属性监听（增删改属性）
- HttpSessionBindingListener 监听对象于 Session 的绑定和解除
- HttpSessionActivationListener 对 Session 数据的钝化和活化的监听
- ServletRequestListener 对 Requesti 对象进行监听（创建、销毁）】
- ServletRequestAttributeListener 对 Requesti 对象中属性的监听（增删改属性）
package priv.noby.listener.listener;
import priv.noby.listener.model.User;
import javax.servlet.ServletContext;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import java.util.HashMap;
@WebListener
public class MyHttpSessionListener implements HttpSessionListener {
public void sessionCreated(HttpSessionEvent httpSessionEvent) {
}
public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
HttpSession session = httpSessionEvent.getSession();
User user = (User)session.getAttribute("user");
ServletContext servletContext = session.getServletContext();
HashMap<String,User> map = (HashMap<String,User>)servletContext.getAttribute("map");
if (user != null) {
map.remove(user.getUsername());
}
}
}
package priv.noby.listener.listener;
import priv.noby.listener.model.User;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import java.util.HashMap;
@WebListener
public class MyServletContextListener implements ServletContextListener {
public void contextInitialized(ServletContextEvent servletContextEvent) {
HashMap<String, User> map = new HashMap<>();
ServletContext servletContext = servletContextEvent.getServletContext();
servletContext.setAttribute("map",map);
}
public void contextDestroyed(ServletContextEvent servletContextEvent) {
}
}
```
```java
package priv.noby.listener.servlet;
import priv.noby.listener.model.User;
import priv.noby.listener.service.UserService;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.util.Map;
@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {
private UserService userService = new UserService();
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
request.setCharacterEncoding("utf-8");
HttpSession session = request.getSession();
ServletContext servletContext = this.getServletContext();
Map<String, User> map = (Map<String, User>) servletContext.getAttribute("map");
String op = request.getParameter("op");
if ("login".equals(op)) {
User user = userService.login(request.getParameter("username"), request.getParameter("password"));
if (user != null) {
session.setAttribute("user", user);
session.setMaxInactiveInterval(180);
map.put(user.getUsername(), user);
response.sendRedirect("/listener/login_list.jsp");
} else {
response.sendRedirect("/listener/login.html");
}
} else if ("out".equals(op)) {
User user = (User) session.getAttribute("user");
if (user != null) {
map.remove(user.getUsername());
session.invalidate();
response.sendRedirect("/listener/login_list.jsp");
}
}
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>login</title>
</head>
<body>
用户登录
<form action="/listener/loginServlet" method="post">
<input type="hidden" name="op" value="login">
用户名：<input type="text" name="username" value="kace">
密码：<input type="password" name="password" value="1"><br>
<input type="submit" value="登录">
</form>
</body>
</html>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>login_list</title>
</head>
<body>
<a href="${pageContext.request.contextPath}/login.html"><h1>登录</h1></a>
<h1>当前用户</h1>
<c:if test="${sessionScope.user!=null}">
<h2>欢迎${sessionScope.user.username}访问网站<a href="${pageContext.request.contextPath}/loginServlet?op=out">退出</a></h2>
</c:if>
<br>
<h1>用户列表</h1>
<c:if test="${not empty applicationScope.map}">
<ul>
<c:forEach items="${applicationScope.map}" var="entry">
<li>
${entry.key}
</li>
</c:forEach>
</ul>
</c:if>
</body>
</html>
