jsp本质：在访问时会被转换为java的类。
?1 /* ?2 ?* Generated by the Jasper component of Apache Tomcat ?3 ?* Version: Apache Tomcat/7.0.92 ?4 ?* Generated at: 2019-02-25 03:41:55 UTC ?5 ?* Note: The last modified time of this file was set to ?6 ?* ??????the last modified time of the source file after ?7 ?* ??????generation to assist with modification tracking. ?8 ?*/ ?9 package org.apache.jsp; 10 ?11 import javax.servlet.*; 12 import javax.servlet.http.*; 13 import javax.servlet.jsp.*; 14 ?15 public final class page_jsp extends org.apache.jasper.runtime.HttpJspBase 16 ????implements org.apache.jasper.runtime.JspSourceDependent { 17 ?18 ?19 ????String str="全局变量"; 20 ?21 ?22 ????public void func1(){ 23 ????System.out.println("全局方法"); 24 } 25 ?26 ?27 ????class C{ 28 ????????private int a; 29 ????????public void f(){ 30 ????????????System.out.println("全局类"); 31 ????????} 32 } 33 ?34 ??private static final javax.servlet.jsp.JspFactory _jspxFactory = 35 ??????????javax.servlet.jsp.JspFactory.getDefaultFactory(); 36 ?37 ??private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants; 38 ?39 ??private volatile javax.el.ExpressionFactory _el_expressionfactory; 40 ??private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager; 41 ?42 ??public java.util.Map<java.lang.String,java.lang.Long> getDependants() { 43 ????return _jspx_dependants; 44 ??} 45 ?46 ??public javax.el.ExpressionFactory _jsp_getExpressionFactory() { 47 ????if (_el_expressionfactory == null) { 48 ??????synchronized (this) { 49 ????????if (_el_expressionfactory == null) { 50 ??????????_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); 51 ????????} 52 ??????} 53 ????} 54 ????return _el_expressionfactory; 55 ??} 56 ?57 ??public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() { 58 ????if (_jsp_instancemanager == null) { 59 ??????synchronized (this) { 60 ????????if (_jsp_instancemanager == null) { 61 ??????????_jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig()); 62 ????????} 63 ??????} 64 ????} 65 ????return _jsp_instancemanager; 66 ??} 67 ?68 ??public void _jspInit() { 69 ??} 70 ?71 ??public void _jspDestroy() { 72 ??} 73 ?74 ??public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response) 75 ????????throws java.io.IOException, javax.servlet.ServletException { 76 ?77 ????final javax.servlet.jsp.PageContext pageContext; 78 ????javax.servlet.http.HttpSession session = null; 79 ????final javax.servlet.ServletContext application; 80 ????final javax.servlet.ServletConfig config; 81 ????javax.servlet.jsp.JspWriter out = null; 82 ????final java.lang.Object page = this; 83 ????javax.servlet.jsp.JspWriter _jspx_out = null; 84 ????javax.servlet.jsp.PageContext _jspx_page_context = null; 85 ?86 ?87 ????try { 88 ??????response.setContentType("text/html; charset=utf-8"); 89 ??????pageContext = _jspxFactory.getPageContext(this, request, response, 90 ??????????????????null, true, 8192, true); 91 ??????_jspx_page_context = pageContext; 92 ??????application = pageContext.getServletContext(); 93 ??????config = pageContext.getServletConfig(); 94 ??????session = pageContext.getSession(); 95 ??????out = pageContext.getOut(); 96 ??????_jspx_out = out; 97 ?98 ??????out.write("\r\n"); 99 ??????out.write("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n");100 ??????out.write("<html>\r\n");101 ??????out.write("<head>\r\n");102 ??????out.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\">\r\n");103 ??????out.write(‘\r‘);104 ??????out.write(‘\n‘);105 ??????out.write(‘\r‘);106 ??????out.write(‘\n‘);107 ??????out.write(‘\r‘);108 ??????out.write(‘\n‘);109 110 ????int a=1234;111 ????String b="java";112 ????out.println(a+b+"局部变量");113 114 ??????out.write("\r\n");115 ??????out.write("<title>Insert title here</title>\r\n");116 ??????out.write("</head>\r\n");117 ??????out.write("<body>\r\n");118 ??????out.print(b );119 ??????out.write("\r\n");120 ??????out.write("</body>\r\n");121 ??????out.write("</html>");122 ????} catch (java.lang.Throwable t) {123 ??????if (!(t instanceof javax.servlet.jsp.SkipPageException)){124 ????????out = _jspx_out;125 ????????if (out != null && out.getBufferSize() != 0)126 ??????????try {127 ????????????if (response.isCommitted()) {128 ??????????????out.flush();129 ????????????} else {130 ??????????????out.clearBuffer();131 ????????????}132 ??????????} catch (java.io.IOException e) {}133 ????????if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);134 ????????else throw new ServletException(t);135 ??????}136 ????} finally {137 ??????_jspxFactory.releasePageContext(_jspx_page_context);138 ????}139 ??}140 }看
15 public final class page_jsp extends org.apache.jasper.runtime.HttpJspBase
可以知道，将jsp页面转换为了一个类继承自org.apache.jasper.runtime.HttpJspBase
在jsp中定义的全局变量、全局方法、类等都是实际在该类中定义。
看
74 ??public void _jspService(
知道，静态代码部分实际会在该函数以java的方式输出。jsp中定义的局部变量会被定义在这里。
该函数就是jsp的实际执行函数。
jsp本质
原文地址：https://www.cnblogs.com/minconding/p/10430195.html