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1.HTTP响应包含三部分：请求行，请求头，请求体。具体结构如图所示
2.状态码
3.contextType的作用是浏览器采用何种方式对响应体进行处理
4.请求转发和重定向：
多个servlet中的跳转有两种方式：
第一种：request.getRequestDispatcher().forward();//请求转发 它是在服务器，即tomcat内部，把请求从第一个servlet转发到第二个servlet.。请求转发是服务器跳转，只会产生一次请求。
第二种:response.sendRedirect；//响应重定向 从浏览器重新发送一个新的请求给servlet，会产生两次请求
设置请求自定义属性值 ：设置请求属性：request.setAttribute(属性名，属性值)
获取属性值：request.getAttribute（属性名）；
5.浏览器cookie:cookie是浏览器保存在本地的文本内容，常用来保存用户登录状态，用户资料等小文本.cookie具有时效性，cookie内容会伴随请求发送给tomcat
package com.xiaoqiang.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * Servlet implementation class FirstServlet */@WebServlet("/Test")public class FirstServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public FirstServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { /* String output=""+"小强
"; response.setContentType("text/xml;charset=utf-8"); response.getWriter().println(output);*/ /*response.sendRedirect("/servlet_study/Test_1");*/ Cookie cookie=new Cookie("user", "xiaoqiang"); response.addCookie(cookie); request.setAttribute("xiaoqiang", "小强"); request.getRequestDispatcher("/Test_1").forward(request, response); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ /*protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub doGet(request, response); }*/} cookies的创建
//获取cookie中的所有值//伪代码Cookie [] cookies=request.getCookies();for(Cookie coo:cookies)
6.session:session（用户会话）用于保存与“浏览器窗口”对应的数据，session的数据存储在tomcat服务器的内存中，具有时效性。session通过
浏览器cookie的sessionId值提取用户数据。
session传递的小例子：
package com.xiaoqiang.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;/** * Servlet implementation class FirstServlet */@WebServlet("/Test")public class FirstServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public FirstServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { /* String output=""+"小强
"; response.setContentType("text/xml;charset=utf-8"); response.getWriter().println(output);*/ /*response.sendRedirect("/servlet_study/Test_1");*/ /* Cookie cookie=new Cookie("user", "xiaoqiang"); response.addCookie(cookie);*/ HttpSession session=request.getSession(); session.setAttribute("xiaoqiang", "小强123"); /* request.setAttribute("xiaoqiang", "小强");*/ request.getRequestDispatcher("/Test_1").forward(request, response); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ /*protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub doGet(request, response); }*/} package com.xiaoqiang.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * Servlet implementation class SecondServlet */@WebServlet("/Test_1")public class SecondServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public SecondServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub String output=""+request.getSession().getAttribute("xiaoqiang")+"
"; response.setContentType("text/html;charset=utf-8"); response.getWriter().println(output); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ /*protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub doGet(request, response); }*/}
7.servletContext:ServletContext(Servlet上下文对象),是web应用全局变量，一个web应用只会创建一个ServletContext对象，
一个ServletContext随着web应用启动而创建
//伪代码ServletContext servletcontext=request.getServletContext();servletcontext.setAuttribute(K,V);
8.java web 三大作用域对象：HttpServletRequest 请求对象 HttpSession 用户会话对象 ServletContext web应用全局对象
它们的作用域和生命周期是依次递增的。
9.解决post请求中的中文乱码：由于tomcat的默认使用字符集ISO-8859-1，属于西欧字符集
解决字符集乱码的核心是把字符集iso-8859-1转化为UTF-8，servlet中请求与响应都需要设置UTF-8。
可以用request.setCharacterEncoding("UTF-8") 方法用于将请求体中的文字字符集转换为UTF-8。
对于tomcat8.x版本以上的get发送中文请求默认是utf-8的格式，无需转换。
response响应也要设置utf-8的编码
10.web.xml中常用配置
在web.xml中写入标签全局变量参数 <context-parm><parm-name>名称</parm-name><parm-value>值</parm-value> </context-parm>
错误跳转<error-page><error-code>错误编码</error-code><location>路径</locathion></error-page>
11.jsp中的九大内置对象
1.request 请求对象 HttpServletRequest
2.response 响应对象 HttpServletRespone
3.session 用户会话 HttpSession
4.application 应用全局变量 ServletContext
5.out 输出对象 PrintWrite
6.page 当前页面对象 this
7.pageContext 页面上下文对象 PageContext
8.config 应用配置对象 ServletConfig
9.exception 应用异常对象 Throwable