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 cnotallow="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>
View Code
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("\n");
113 out.write("\n");
114 out.write("<html>\n");
115 out.write(" <head>\n");
116 out.write(" <title>$Title$</title>\n");
117 out.write(" </head>\n");
118 out.write(" <body>\n");
119 out.write(" ");
120
121 int a=10;
122 String s="hello";
123
124 out.write("\n");
125 out.write("\n");
126 out.write(" <div>a=");
127 out.print(a);
128 out.write("</div>\n");
129 out.write(" <div>s=");
130 out.print(s);
131 out.write("</div>\n");
132 out.write("\n");
133 out.write(" ");
134 out.write("\n");
135 out.write(" <div>d=");
136 out.print(d);
137 out.write("</div>\n");
138 out.write(" </body>\n");
139 out.write("</html>\n");
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 }
View Code
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
