jsp---->jsp执行过程

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JSP 的执行过程

(1) 客户端发出Request (请求)；
(2) JSP Container 将JSP转译成Servlet的源代码；
(3) 将产生的Servlet 的源代码经过编译后，并加载到内存执行；
(4) 把结果Response (响应)至客户端。

在执行 JSP 网页时，通常可分为两个时期：转译时期(Translation Time)和请求时期(Request Time)
转译时期：JSP网页转译成Servlet类。
请求时期：Servlet类执行后，响应结果至客户端。

注：

转译期间主要做了两件事情：将JSP网页转译为 Servlet 源代码(.java)，此段称为转译时期(Translation time)；将Servlet源代码(.java)编译成 Servlet 类(.class)，此段称为编译时期(Compilation time)。

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <base href="<%=basePath%>">        <title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">-->  </head>    <body>    This is my JSP page. <br>  </body></html>

在tomcat安装目录\work\Catalina\localhost\项目名称下会自动产生index_jsp.java和index_jsp.class文件

package org.apache.jsp;import javax.servlet.*;import javax.servlet.http.*;import javax.servlet.jsp.*;import java.util.*;public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase    implements org.apache.jasper.runtime.JspSourceDependent {  private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();  private static java.util.List _jspx_dependants;  private javax.el.ExpressionFactory _el_expressionfactory;  private org.apache.AnnotationProcessor _jsp_annotationprocessor;  public Object getDependants() {    return _jspx_dependants;  }  public void _jspInit() {    _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();    _jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor.class.getName());  }  public void _jspDestroy() {  }  public void _jspService(HttpServletRequest request, HttpServletResponse response)        throws java.io.IOException, ServletException {    PageContext pageContext = null;    HttpSession session = null;    ServletContext application = null;    ServletConfig config = null;    JspWriter out = null;    Object page = this;    JspWriter _jspx_out = null;    PageContext _jspx_page_context = null;    try {      response.setContentType("text/html;charset=ISO-8859-1");      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("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">\r\n");      out.write("<html>\r\n");      out.write("  <head>\r\n");      out.write("    <base href=\"");      out.print(basePath);      out.write("\">\r\n");      out.write("    \r\n");      out.write("    <title>My JSP 'index.jsp' starting page</title>\r\n");      out.write("\t<meta http-equiv=\"pragma\" content=\"no-cache\">\r\n");      out.write("\t<meta http-equiv=\"cache-control\" content=\"no-cache\">\r\n");      out.write("\t<meta http-equiv=\"expires\" content=\"0\">    \r\n");      out.write("\t<meta http-equiv=\"keywords\" content=\"keyword1,keyword2,keyword3\">\r\n");      out.write("\t<meta http-equiv=\"description\" content=\"This is my page\">\r\n");      out.write("\t<!--\r\n");      out.write("\t<link rel=\"stylesheet\" type=\"text/css\" href=\"styles.css\">\r\n");      out.write("\t-->\r\n");      out.write("  </head>\r\n");      out.write("  \r\n");      out.write("  <body>\r\n");      out.write("    This is my JSP page. <br>\r\n");      out.write("  </body>\r\n");      out.write("</html>\r\n");    } catch (Throwable t) {      if (!(t instanceof 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);    }  }}

jspInit() 执行一次初始化；
jspService() 进行请求处理；
jspDestroy() JSP引擎从服务器中删除servlet实例时，会调用jspDestroy();