JSP

jsp组成

  • html + java + jsp标签
  • jsp中无须创建即可使用的对象(9个)
  • java脚本格式
    • <%...%> java代码片段
    • <%=...%> java表达式
    • <%!...%> 声明

简单的例子

  • 一个数据提交的表单



  • NumberServlet
  public void doPost(HttpServletRequest request, HttpServletResponse response)
       throws ServletException, IOException {

     String s1 = request.getParameter("num1");
     String s2 = request.getParameter("num2");
     
     request.setAttribute("result", s1+s2);
     request.getRequestDispatcher("./jsps/result.jsp").forward(request, response);
   } 
- - -
  • 结果显示的jsp
    
      result:  <%=request.getAttribute("result") %>
    
    


jsp原理

  • 第一次访问jsp的时候回讲jsp编译成java --》 class
  • jsp其实是一个Servlet 。tomcat work下面
  • jsp代码和编译后的java代码
  
    This is my JSP page. 
hello <% int a = 100; out.print(a); a++; %> <% out.print(a); a++; %> <%! int a = 90; %> <% out.print(this.a++); %>
- - -
    public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
      implements org.apache.jasper.runtime.JspSourceDependent {


        int a = 90;
      
    private static final javax.servlet.jsp.JspFactory _jspxFactory =
            javax.servlet.jsp.JspFactory.getDefaultFactory();

    private static java.util.List _jspx_dependants;

    private javax.el.ExpressionFactory _el_expressionfactory;
    private org.apache.tomcat.InstanceManager _jsp_instancemanager;

    public java.util.List getDependants() {
      return _jspx_dependants;
    }

    public void _jspInit() {
      _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
      _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
    }

    public void _jspDestroy() {
    }

    public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
          throws java.io.IOException, javax.servlet.ServletException {

      final javax.servlet.jsp.PageContext pageContext;
      javax.servlet.http.HttpSession session = null;
      final javax.servlet.ServletContext application;
      final javax.servlet.ServletConfig config;
      javax.servlet.jsp.JspWriter out = null;
      final java.lang.Object page = this;
      javax.servlet.jsp.JspWriter _jspx_out = null;
      javax.servlet.jsp.PageContext _jspx_page_context = null;


      try {
        response.setContentType("text/html;charset=utf-8");
        pageContext = _jspxFactory.getPageContext(this, request, response,
              null, true, 8192, true);
        _jspx_page_context = pageContext;
        application = pageContext.getServletContext();
        config = pageContext.getServletConfig();
        session = pageContext.getSession();
        out = pageContext.getOut();
        _jspx_out = out;

        out.write('\r');
        out.write('\n');

  String path = request.getContextPath();
  String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

        out.write("\r\n");
        out.write("\r\n");
        out.write("\r\n");
        out.write("\r\n");
        out.write("  \r\n");
        out.write("    ");
        out.write("\r\n");
        out.write("    \r\n");
        out.write("    My JSP 'index.jsp' starting page\r\n");
        out.write("\t\r\n");
        out.write("\t\r\n");
        out.write("\t    \r\n");
        out.write("\t\r\n");
        out.write("\t\r\n");
        out.write("\t\r\n");
        out.write("  \r\n");
        out.write("  \r\n");
        out.write("  \r\n");
        out.write("    This is my JSP page. 
\r\n"); out.write(" hello\r\n"); out.write(" "); int a = 100; out.print(a); a++; out.write("\r\n"); out.write(" "); out.print(a); a++; out.write("\r\n"); out.write(" "); out.write("\r\n"); out.write(" "); out.print(this.a++); out.write("\r\n"); out.write(" \r\n"); out.write("\r\n"); } catch (java.lang.Throwable t) { if (!(t instanceof javax.servlet.jsp.SkipPageException)){ out = _jspx_out; if (out != null && out.getBufferSize() != 0) try { out.clearBuffer(); } catch (java.io.IOException e) {} if (_jspx_page_context != null) _jspx_page_context.handlePageException(t); } } finally { _jspxFactory.releasePageContext(_jspx_page_context); } } }

JSP三大指令

<% @ 指令名 attr1="" attr2="" %>

  • page
    • pageEncoding 指定当前jsp页面的编码(只要pageEncoding的编码和文件的编码一致就不会由乱码,jsp-->class的时候会去读取这个属性)
    • contentType 添加一个响应头
    • 这两个只要一个就可以了
      <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
      ```
    • import
      <%@ page import="class1,class2,class3"%>
    • errorPage isErrorPage
  • include 静态包含
    <%@ include file="*.jsp"%>
    jsp编译成java文件时完成,他们共同生成一个java文件
  • taglib 导入标签库
    • prefix 前缀
    • uri 标签库的位置
    • <%@taglib prefix="s" uri="/struts-tags"%>

JSP动作标签


Cookie

由服务器创建保存到客户端浏览器的一个键值对,服务器保存cookie的相应头:Set-Cookie: key=value Set-Cookie: key1=value1 当浏览器请求服务器时,会把该服务器保存的Cookie随请求发送给服务器: Cookie: key=value; key1=value1

  • 一个Cookie最大4KB

  • 一个服务器最多向一个浏览器保存20个Cookie

  • 一个浏览器最多保存300个Cookie

  • Cookie的maxAge cookie.setMaxAge(int)

    • maxAge > 0 浏览器会保存到硬盘上 单位 S
    • maxAge < 0 只会保存到内存中 默认
    • maxAge = 0 需要删除该Cookie
  • Cookie的path


    JSP_第1张图片
    谷歌浏览器的cookie

javaWeb Cookie

response.addCookie();
request.getCookies();

JSP中使用Cookie

//保存cookie
Cookie nameCookie = new Cookie("name","dapi");
Cookie numberCookie = new Cookie("number","12101010320");
response.addCookie(nameCookie);
response.addCookie(numberCookie);
    
 //获取cookie
 Cookie[] cookies = request.getCookies();
 if(cookies != null){
    for(int i=0;i < cookies.length;i++){
    out.print(cookies[i].getName()+"  "+cookies[i].getValue()+"
"); } }

HttpSession

  • 由javaWeb提供用来会话(一个用户对服务器的连续请求,多次请求没有关闭浏览器)跟踪的类
  • session是服务器端对象保存在服务器端
  • HttpSession是Servlet三大域之一(request,session,application)
  • 底层依赖Cookie或者URL重写
//servlet
request.getSession();
//jsp 可以直接使用 session
session.setAttribute("name", "xx");
session.getAttribute("name");
session.removeAttribute("name");

request.getSession() 首先是会获取Cookie中的sessionId,如果id不存在,创建session保存sessionid,如果存在则通过id找session,如果没找到则创建session并将id保存到cookie中。
sessionId保存的时候maxAge为-1
web.xml中可以配置session最大不活动时间

30



Url重写

response.encodeURL(String url);//将cookie --> params


Nothing is certain in this life. The only thing i know for sure is that. I love you and my life. That is the only thing i know. have a good day

:)

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