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

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简单的例子

• 一个数据提交的表单

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• 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") %>
  
  

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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("    \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);
      }
    }
  }

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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"%>

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JSP动作标签

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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

  
  
  

  谷歌浏览器的cookie

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javaWeb Cookie

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

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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()+"
");
    }
 }

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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

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Url重写

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

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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

:)