一、概念部分
JSP，即Java Server Pages首字母的缩写，Java服务器页面，即运行在服务器端的页面。它是由Sun公司倡导，许多国际性大公司一起参与，建立的一种动态网页技术。JSP技术是在传统的静态网页HTML页面中插入Java代码片段和JSP标签后形成的一种文件，其后缀名为.jsp。使用JSP开发的Web应用和Java一样是跨平台的，也就是既能在linux上运行，也能在其它操作系统上运行。
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。
三、jsp页面组成部分图解
四、示例
4.1我的第一个jsp页面
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_jsp</title></head><body>My First jsp!</body></html>
4.2经Tomcat采用JSP规范将上面jsp页面翻译成的.java源码
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<java.lang.String,java.lang.Long> _jspx_dependants; ?private volatile javax.el.ExpressionFactory _el_expressionfactory; ?private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager; ?public java.util.Map<java.lang.String,java.lang.Long> 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("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n"); ?????out.write("<html>\r\n"); ?????out.write("<head>\r\n"); ?????out.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\">\r\n"); ?????out.write("<title>first_jsp</title>\r\n"); ?????out.write("</head>\r\n"); ?????out.write("<body>\r\n"); ?????out.write("My First jsp!\r\n"); ?????out.write("</body>\r\n"); ?????out.write("</html>"); ???} 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); ???} ?}}jsp简介
原文地址：https://www.cnblogs.com/aeon/p/10306822.html