Servlet
在web.xml容器中的加载
<servlet>
<servlet-name>servlets</servlet-name><!--一般用类名首字母小写表示-->
<servlet-class>cn.ii.user.web.UserServlet</servlet-class><!--全限定类名(包+类名)-->
</servlet>
<!--Servlet映射-->
<servlet-mapping>
<servlet-name>servlets</servlet-name><!--与上名同-->
<url-pattern>/servlets</url-pattern><!--访问时所用名-->
</servlet-mapping>我的理解是：让web容器加载这个类到tomcat上，通过映射，定义的名字，进行访问！
Servlet:java代码
一,实现Servlet接口
import javax.servlet.*;
import java.io.IOException;
public class BServlet implements Servlet {
//初始化即产生
public void init(ServletConfig servletConfig) throws ServletException {
System.out.println("Servlet出生");
}
//ServletConfig:上下文对象的获取
public ServletConfig getServletConfig() {
return null;
}
//请求方法
public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
System.out.println("Servlet正在处理请求");
}
//servlet的一些信息
public String getServletInfo() {
return null;
}
//销毁即死去
public void destroy() {
System.out.println("可怜的Servlet去世了");
}二.继承GenericServlet
import javax.servlet.*;
import java.io.IOException;
public class BServlet extends GenericServlet {
//初始化即产生
public void init(ServletConfig servletConfig) throws ServletException {
}
//ServletConfig:上下文对象的获取
public ServletConfig getServletConfig() {
return null;
}
//请求方法
public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
}
//Servlet的一些信息
public String getServletInfo() {
return null;
}
//销毁即死去
public void destroy() {
}
}三.继承HttpServlet(用的最多)
import javax.servlet.*;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
/**
* 将service请求细化成get与post请求,
*/
public class BServlet extends HttpServlet {
//get请求(明文)
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setAttribute("x","");//Request域，有效范围：单次请求内有效
req.getSession().setAttribute("x","");//Session域，有效范围：浏览器与服务器的一次会话中有效，不同浏览器Session保留时间不同！
req.getRequestDispatcher("index.jsp").forward(req,resp);//转发，配合Request域使用！地址栏不变，还是一次请求。
resp.sendRedirect("index.jsp");//重定向,请求改变，地址栏改变！
resp.setContentType("text/html;charset=UTF-8");//设置响应类型
resp.getWriter().print("IO");//响应流
//applicationcontext域：服务器运行中有效，重启或关闭后失效
//page域：在本页面内有效（jsp中）
req.getHeaderNames();//请求头信息(全部)
//jsp九大内置对象：四个域 + response响应对象 + out输出对象 + config配置对象 + exception异常对象 + page页面对象
}
//post请求(隐藏的)
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doPost(req, resp);
}
}jsp = Servlet
jstl:标签库(为了更好的让前后端分离)
<%--设置本页编码,后端语言，响应编码--%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%--导入jar包--%>
<%@ page import="java.util.List"%>
<%--导入jstl标签库,前缀为c,由':'分离--%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<head>
<title>bug</title>
</head>
<body>
<!--forEach遍历List集合中的User对象-->
<c:forEach items="${list}" var="l">
${l.username}<br/>
</c:forEach>
<% //往四大域中添加值！
//用El表达式取(优先级,由以下顺序，由大到小)
pageContext.setAttribute("message","0");
request.setAttribute("message","1");
session.setAttribute("message","2");
application.setAttribute("message","3");
%>
<!--EL表达式-->
${message}
<!--if语句，test中是判断条件-->
<c:if test="${w} == 0">
</c:if>
<!--switch语句-->
<c:choose>
<c:when test="${x} == 1">1</c:when>
<c:when test="${x} == 2">2</c:when>
<c:otherwise>3</c:otherwise>
</c:choose>
<!--jsp内置标签转发-->
<jsp:forward page="login.html"></jsp:forward>
</body>
</html>过滤器在web容器中的加载
<filter>
<filter-name>userFilter</filter-name>
<filter-class>cn.ii.user.UserFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>userFilter</filter-name>
<url-pattern>/*</url-pattern><!--过滤范围（这里是全部资源）-->
</filter-mapping>Filter：过滤器
import javax.servlet.*;
import java.io.IOException;
public class BBFilter implements Filter {
public void destroy() {
System.out.println("Filter销毁");
}
public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
System.out.println("过滤内容");
//可以在这里实现，解决中文乱码问题！
}
public void init(FilterConfig config) throws ServletException {
System.out.println("Filter出生");
}
}拦截器在web容器中的加载
<listener>
<listener-class>cn.ii.user.ListenerS</listener-class>
</listener>拦截器实现
(可以实现一些资源监控,用户权限监控)
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionBindingEvent;
public class ListenerS implements ServletContextListener,
HttpSessionListener, HttpSessionAttributeListener {
// Public constructor is required by servlet spec
public ListenerS() {
}
// -------------------------------------------------------
// ServletContextListener implementation
// -------------------------------------------------------
//监控context：上下文对象的创建
public void contextInitialized(ServletContextEvent sce) {
/* This method is called when the servlet context is
initialized(when the Web application is deployed).
You can initialize servlet context related data here.
*/
}
//监控context：上下文对象的销毁
public void contextDestroyed(ServletContextEvent sce) {
/* This method is invoked when the Servlet Context
(the Web application) is undeployed or
Application Server shuts down.
*/
}
// -------------------------------------------------------
// HttpSessionListener implementation
// -------------------------------------------------------
//监控session：会话对象的创建
public void sessionCreated(HttpSessionEvent se) {
/* Session is created. */
}
//监控session：会话对象的销毁
public void sessionDestroyed(HttpSessionEvent se) {
/* Session is destroyed. */
}
// -------------------------------------------------------
// HttpSessionAttributeListener implementation
// -------------------------------------------------------
//监控session：会话中的属性添加
public void attributeAdded(HttpSessionBindingEvent sbe) {
/* This method is called when an attribute
is added to a session.
*/
}
//监控session：会话中的属性移除
public void attributeRemoved(HttpSessionBindingEvent sbe) {
/* This method is called when an attribute
is removed from a session.
*/
}
//监控session：会话中的属性取代
public void attributeReplaced(HttpSessionBindingEvent sbe) {
/* This method is invoked when an attibute
is replaced in a session.
*/
}
}Servlet3.0以后Servlet等在web.xml中的配置实现注解取代
我认为TomCat等服务器，底层实现了注解扫描器！读取整个web项目中的class文件，来加载！
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