JSP文件的本质是Servlet。只不过JSP与Servlet不同的是:JSP是专门用于数据展示的Servlet，其有特殊的的写法。而普通的Servlet是用于完成业务逻辑处理的。由于Servlet是运行在单例多线程环境下的，所以JSP同样也是运行在单例多线程环境下的。
二、JSP规范
将JSP页面翻译为Servlet的过程是由Tomcat完成的。在Tomcat中内置了一个JSP翻译引擎，当第一次访问该JSP页面时，该翻译引擎会将JSP页面翻译为Servlet的.java源文件，再将该.java源文件编译为.class字节码文件进行运行。
SUN公司制定的Java EE规范中包含两个很重要的子规范：Servlet规范和JSP规范。其中JSP规范中就包含了如何将JSP页面翻译为Servlet。例如，JSP页面中的HTML、CSS、Javascript及普通文本部分军徽被翻译到out.write()中。Tomcat中的JSP翻译引擎，就遵循了这个JSP规范。
发布到tomcat后该页面存放在：..\\workspace\\.metadata\\.plugins\\org.eclipse.wst.server.core\\tmp0\\wtpwebapps\\jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>first_jsptitle>
head>
<body>
My First jsp!
body>
html>
存放地址：..\\workspace\\.metadata\\.plugins\\org.eclipse.wst.server.core\\tmp0\\work\\Catalina\\localhost\\jsp\\org\\apache\\jsp
/*
* Generated by the Jasper component of Apache Tomcat
* Version: Apache Tomcat/7.0.85
* Generated at: 2019-01-22 16:01:50 UTC
* Note: The last modified time of this file was set to
* the last modified time of the source file after
* generation to assist with modification tracking.
*/
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
private static final javax.servlet.jsp.JspFactory _jspxFactory =
javax.servlet.jsp.JspFactory.getDefaultFactory();
private static java.util.Map _jspx_dependants;
private volatile javax.el.ExpressionFactory _el_expressionfactory;
private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager;
public java.util.Map getDependants() {
return _jspx_dependants;
}
public javax.el.ExpressionFactory _jsp_getExpressionFactory() {
if (_el_expressiOnfactory== null) {
synchronized (this) {
if (_el_expressiOnfactory== null) {
_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
}
}
}
return _el_expressionfactory;
}
public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() {
if (_jsp_instancemanager == null) {
synchronized (this) {
if (_jsp_instancemanager == null) {
_jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
}
}
}
return _jsp_instancemanager;
}
public void _jspInit() {
}
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\\n");
out.write("\\r\\n");
out.write("\\r\\n");
out.write("\\r\\n");
out.write("\\r\\n");
out.write("\\r\\n");
out.write("\\r\\n");
out.write("\\r\\n");
out.write("My First jsp!\\r\\n");
out.write("\\r\\n");
out.write("");
} catch (java.lang.Throwable t) {
if (!(t instanceof javax.servlet.jsp.SkipPageException)){
out = _jspx_out;
if (out != null && out.getBufferSize() != 0)
try {
if (response.isCommitted()) {
out.flush();
} else {
out.clearBuffer();
}
} catch (java.io.IOException e) {}
if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
else throw new ServletException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
}
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