javaweb过滤器与监听器
一、过滤器程序的基本结构、web.xml文件的配置过程和过滤器的执行过程
FirstFilter
filter.FirstFilter
course
Java EE
FirstFilter
/test.html
Title
这是一个测试过滤器
package filter;
import javax.servlet.*;
import java.io.IOException;
import java.io.PrintWriter;
public class FirstFilter implements Filter { //实现Filter接口
FilterConfig config = null;//定义一个FilterConfig对象为类的实例变量
public void init(FilterConfig filterConfig) throws ServletException {
config = filterConfig;//获取FilterConfig对象引用
}
public void destroy() {
config = null;
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
String str = config.getInitParameter("course");//获取过滤器初始参数
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
out.println("前置程序块
");
out.println("过滤器初始参数:course=" + str + "
");
chain.doFilter(request, response);//调用"过滤器链"方法
out.println("
后置程序块
");
}
}
过滤器需要实现Filter接口，并重写Filter的三个方法：init()、destory()、doFilter()
过滤器的执行顺序：多个过滤器的拦截路径相同时，首先按照
二、注解配置过滤器：字符编码过滤器及权限验证过滤器的实现
package filter;
import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import jakarta.servlet.annotation.WebInitParam;
import jakarta.servlet.annotation.WebServlet;
import java.io.IOException;
@WebFilter(filterName = "EncodingFilter", urlPatterns = "/*",
initParams = {@WebInitParam(name = "encode", value = "UTF-8")})
public class EncodingFilter implements Filter {
private String encode = null;
@Override
public void init(FilterConfig filterConfig) throws ServletException {
encode = filterConfig.getInitParameter("encode");
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
servletRequest.setCharacterEncoding(encode);
servletResponse.setContentType("text/html;charset="+encode);
filterChain.doFilter(servletRequest, servletResponse);
}
@Override
public void destroy() {
Filter.super.destroy();
}
}
package filter;
import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;
import java.io.IOException;
@WebFilter(filterName = "ValidationFilter", value = "/admin/*")
public class ValidationFilter implements Filter {
@Override
public void init(FilterConfig Config) throws ServletException {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpSession session = ((HttpServletRequest) request).getSession();
if(session.getAttribute("user") == null){
((HttpServletResponse) response).sendRedirect("login.jsp");
}
chain.doFilter(request, response);
}
@Override
public void destroy() {
Filter.super.destroy();
}
}
package servlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
/**
* Servlet implementation class LoginServlet
*/
@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String account = request.getParameter("account");
String password = request.getParameter("password");
if (account.equals("Sarah") && password.equals("123456")) {
request.getSession().setAttribute("user", account);
response.sendRedirect("admin/showAllBooks");
} else {
response.sendRedirect("login.jsp");
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
三、application、session两类对象的创建与销毁时间监听
package listener;
import jakarta.servlet.ServletContextEvent;
import jakarta.servlet.ServletContextListener;
import jakarta.servlet.ServletRequestEvent;
import jakarta.servlet.ServletRequestListener;
import jakarta.servlet.annotation.WebListener;
import jakarta.servlet.http.HttpSessionEvent;
import jakarta.servlet.http.HttpSessionListener;
//添加监听器注解
@WebListener
//由MyListener类实现ServletContext、HttpSession、ServletRequest三类对象创建、销毁事件的监听
public class MyListener implements ServletContextListener, HttpSessionListener, ServletRequestListener {
public void contextInitialized(ServletContextEvent sce) {
System.out.println("\n ServletContext对象被创建了");
}
public void contextDestroyed(ServletContextEvent sce) {
System.out.println("\n ServletContext对象被销毁了");
}
public void sessionCreated(HttpSessionEvent se) {
System.out.println("\n HttpSession对象被创建了");
}
public void sessionDestroyed(HttpSessionEvent se) {
System.out.println("\n HttpSession对象被销毁了");
}
public void requestDestroyed(ServletRequestEvent sre) {
System.out.println("\n servletRequest对象被销毁了");
}
public void requestInitialized(ServletRequestEvent sre) {
System.out.println("\n servletRequest对象被创建了");
}
}
package servlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
@WebServlet(value="/test")
public class TestServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
HttpSession session = request.getSession();//得到会话:如果没有会话,就创建一个
PrintWriter out = response.getWriter();
out.println("");
out.println("");
out.println("Servlet事件监听 ");
out.println("");
out.println("");
out.println("创建了一个会话!
");
out.println("");
out.println("");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
servlet事件监听器
用html文档测试servlet事件监听器
(1)启动Tomcat服务器(如果Tomcat已启动，请先关闭)，观察控制台输出的信息。这说明了什么？
答：服务器启动时执行contextInitialized(ServletContextEvent sce)方法。首先servletContext全局对象被创建
(2)打开浏览器，输入http://127.0.0.1:8080/lab6_3/index.html网址，观察控制台输出的信息。这又说明了什么？
答：执行requestInitialized(ServletRequestEvent sre)方法，servletRequest对象被创建，随后自动执行requestDestory(ServletRequestEvent sre)方法，servletRequest对象被销毁了
(3)打开浏览器，输入http://127.0.0.1:8080/lab6_3/test网址，观察控制台输出的信息。这又说明了什么？
答：执行requestInitialized(ServletRequestEvent sre)方法，servletRequest对象被创建，紧接着执行了sessionCreated(HttpSessionEvent se)方法，HttpSession对象被创建，最后自动执行requestDestroyed(ServletRequestEvent sre)方法，servletRequest对象被销毁
问题：web.xml中的如下标记实现什么功能？
(4)过1分钟之后，再次观察控制台输出的信息。这又说明了什么？
答：实现了1分钟后执行sessionDestoryed(HttpSessionEvent se)方法
请总结application、session两类对象创建、销毁事件监听的方法与步骤。注意：不同监听接口、事件、方法的差异。
答：首先要实现ServletContextListener、HttpSessionListener、ServletRequestListener。重写三类对象创建和销毁的事件以便监听。当触发相应的Servlet对象就可以实现相应的监听。
- ServletContextListener：监听application的产生与销毁
- HttpSessionListener：监听session的产生与销毁
- ServletRequestListener：监听request的产生与销毁
四、application、session两类对象属性变化事件监听
package listener;
import jakarta.servlet.*;
import jakarta.servlet.http.*;
//由MySttributeListener类实现application、session两类对象属性变化事件的监听
public class MyAttributeListener implements ServletContextAttributeListener, HttpSessionAttributeListener {
public void attributeAdded(ServletContextAttributeEvent scae) {
System.out.println("\n application对象中增加了一个名为" + scae.getName()
+ "的属性,该属性值为" + scae.getValue());
}
public void attributeRemoved(ServletContextAttributeEvent scae) {
System.out.println("\n application对象中的" + scae.getName() + "属性被删除了\n");
}
public void attributeReplaced(ServletContextAttributeEvent scae) {
System.out.println("\n application对象中" + scae.getName() + "的属性值被替换成了"
+ scae.getServletContext().getAttribute(scae.getName()));
}
public void attributeAdded(HttpSessionBindingEvent hbe) {
System.out.println("\n session对象中增加了一个名为" + hbe.getName()
+ "的属性，该属性值为" + hbe.getValue());
}
public void attributeRemoved(HttpSessionBindingEvent hbe) {
System.out.println("\n session对象中的" + hbe.getName() + "属性被删除了\n");
}
public void attributeReplaced(HttpSessionBindingEvent hbe) {
System.out.println("\n session对象中" + hbe.getName() + "的属性值被替换成了"
+ hbe.getSession().getAttribute(hbe.getName()));
}
}
listener.MyAttributeListener
index.jsp
测试session对象属性变化
<%@ page contentType="text/html;charset=gb2312"%>
这是一个测试session对象属性变化的页面
<%
session.setAttribute("width", "98.7654");
session.setAttribute("width", "9876.54");
session.removeAttribute("width");
%>
测试application对象属性变化
<%@ page contentType="text/html;charset=gb2312"%>
这是一个测试application对象属性变化的页面
<%
application.setAttribute("length", "123.45");
application.setAttribute("length", "1234.5");
application.removeAttribute("length");
%>
application、session两种事件对象的getName()、getValue()的功能是什么？如何获得变化过的属性值？
答：getName()获取application或session的属性名；getValue()获取application或session的属性值。
application对象获得变化过的属性值：getServletContext().getAttribute(getName())
session对象获得变化过的属性值：getSession().getAttribute(getName());
(1)打开浏览器，输入http://127.0.0.1:8080/lab6_4/ServletContextAttributeTest.jsp网址，观察控制台输出的信息。这说明了什么？
答：application对象设置属性时调用attributeAdded(ServletContextAttributeEvent scae)方法，重新更改属性时调用attributeReplaced(ServletContextAttributeEvent scae)方法，删除属性时调用attributeRemoved(ServletContextAttributeEvent scae)方法
(2)在浏览器输入http://127.0.0.1:8080/lab6_4/HttpSessionAttributeTest.jsp网址，观察控制台输出的信息。这又说明了什么？
答：session对象设置属性时调用attributeAdded(HttpSessionBindingEvent hbe)方法，重新更改属性时调用attributeReplaced(HttpSessionBindingEvent hbe)方法，删除属性时调用attributeRemoved(HttpSessionBindingEvent hbe)方法
请总结application、session两类对象属性变化事件监听的方法与步骤。注意：不同监听接口、事件差异，在方法名上有什么相似之处？
答：session对象和application对象都是设置属性时调用attributeAdded()方法，重新更改属性时调用attributeReplaced()方法，删除属性时调用attributeRemoved()方法。
ServletContextAttributeListener和HttpSessionAttributeListener包含的方法名称相同，只是参数不同。