1 jsp的本质是Servlet
jsp执行原理：
1.1在idea中启动tomcat:
1.1.1新建子模块项目：
1.1.2编写jsp代码：
1 <%-- 2 Created by IntelliJ IDEA. 3 User: Administrator 4 Date: 2019/6/15 0015 5 Time: 21:53 6 To change this template use File | Settings | File Templates. 7 --%> 8 <%@ page contentType="text/html;charset=UTF-8" language="java" %> 9 <html> 10 <head> 11 <title>$Title$</title> 12 </head> 13 <body> 14 <% 15 int a=10; 16 String s="hello"; 17 %> 18 19 <div>a=<%=a%></div> 20 <div>s=<%=s%></div> 21 22 <%! 23 double d=5.21; 24 %> 25 <div>d=<%=d%></div> 26 </body> 27 </html>
1.1.3找到index.jsp生成的.java文件
（index_jsp.java）文件代码：
1 /* 2 * Generated by the Jasper component of Apache Tomcat 3 * Version: Apache Tomcat/8.5.32 4 * Generated at: 2019-06-16 02:07:24 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 index_jsp extends org.apache.jasper.runtime.HttpJspBase 16 implements org.apache.jasper.runtime.JspSourceDependent, 17 org.apache.jasper.runtime.JspSourceImports { 18 19 20 double d=5.21; 21 22 private static final javax.servlet.jsp.JspFactory _jspxFactory = 23 javax.servlet.jsp.JspFactory.getDefaultFactory(); 24 25 private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants; 26 27 private static final java.util.Set<java.lang.String> _jspx_imports_packages; 28 29 private static final java.util.Set<java.lang.String> _jspx_imports_classes; 30 31 static { 32 _jspx_imports_packages = new java.util.HashSet<>(); 33 _jspx_imports_packages.add("javax.servlet"); 34 _jspx_imports_packages.add("javax.servlet.http"); 35 _jspx_imports_packages.add("javax.servlet.jsp"); 36 _jspx_imports_classes = null; 37 } 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 java.util.Set<java.lang.String> getPackageImports() { 47 return _jspx_imports_packages; 48 } 49 50 public java.util.Set<java.lang.String> getClassImports() { 51 return _jspx_imports_classes; 52 } 53 54 public javax.el.ExpressionFactory _jsp_getExpressionFactory() { 55 if (_el_expressionfactory == null) { 56 synchronized (this) { 57 if (_el_expressionfactory == null) { 58 _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); 59 } 60 } 61 } 62 return _el_expressionfactory; 63 } 64 65 public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() { 66 if (_jsp_instancemanager == null) { 67 synchronized (this) { 68 if (_jsp_instancemanager == null) { 69 _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig()); 70 } 71 } 72 } 73 return _jsp_instancemanager; 74 } 75 76 public void _jspInit() { 77 } 78 79 public void _jspDestroy() { 80 } 81 82 public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response) 83 throws java.io.IOException, javax.servlet.ServletException { 84 85 final java.lang.String _jspx_method = request.getMethod(); 86 if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method) && !javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) { 87 response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSPs only permit GET POST or HEAD"); 88 return; 89 } 90 91 final javax.servlet.jsp.PageContext pageContext; 92 javax.servlet.http.HttpSession session = null; 93 final javax.servlet.ServletContext application; 94 final javax.servlet.ServletConfig config; 95 javax.servlet.jsp.JspWriter out = null; 96 final java.lang.Object page = this; 97 javax.servlet.jsp.JspWriter _jspx_out = null; 98 javax.servlet.jsp.PageContext _jspx_page_context = null; 99 100 101 try { 102 response.setContentType("text/html;charset=UTF-8"); 103 pageContext = _jspxFactory.getPageContext(this, request, response, 104 null, true, 8192, true); 105 _jspx_page_context = pageContext; 106 application = pageContext.getServletContext(); 107 config = pageContext.getServletConfig(); 108 session = pageContext.getSession(); 109 out = pageContext.getOut(); 110 _jspx_out = out; 111 112 out.write(" "); 113 out.write(" "); 114 out.write("<html> "); 115 out.write(" <head> "); 116 out.write(" <title>$Title$</title> "); 117 out.write(" </head> "); 118 out.write(" <body> "); 119 out.write(" "); 120 121 int a=10; 122 String s="hello"; 123 124 out.write(" "); 125 out.write(" "); 126 out.write(" <div>a="); 127 out.print(a); 128 out.write("</div> "); 129 out.write(" <div>s="); 130 out.print(s); 131 out.write("</div> "); 132 out.write(" "); 133 out.write(" "); 134 out.write(" "); 135 out.write(" <div>d="); 136 out.print(d); 137 out.write("</div> "); 138 out.write(" </body> "); 139 out.write("</html> "); 140 } catch (java.lang.Throwable t) { 141 if (!(t instanceof javax.servlet.jsp.SkipPageException)){ 142 out = _jspx_out; 143 if (out != null && out.getBufferSize() != 0) 144 try { 145 if (response.isCommitted()) { 146 out.flush(); 147 } else { 148 out.clearBuffer(); 149 } 150 } catch (java.io.IOException e) {} 151 if (_jspx_page_context != null) _jspx_page_context.handlePageException(t); 152 else throw new ServletException(t); 153 } 154 } finally { 155 _jspxFactory.releasePageContext(_jspx_page_context); 156 } 157 } 158 }
1.1.4代码解析
只简单说明下，一点代码。div标签的内容会被解析如下代码：（红色框）
1.2 在直接手动启动tomcat，查找:
1.2.1手动启动tomcat
1.2.2 生成文件所在目录
