1.jsp原理图
其步骤如下:
1.jsp引擎将jsp文件翻译为Servlet源程序;
2.之后又将Servlet源程序编译为.class类文件;
其中:
1.Jsp引擎是通常一个Servlet程序,Tomcat中的jsp引擎就是org.apache.jasper.servlet.JspServlet;
2.在Tomcat中编译的源文件和.class文件放在”[TOMCAT_HOME]\work\Catalina\[主机名,如localhost]\应用程序名称” 目录下;
3.默认情况下,第一次访问某jsp文件时,才对该jsp文件进行翻译、编译,所以较慢。不过在以后的访问中将不会在出现该情况,因为已经被编译过了,呵呵。
2.jsp相关类
2.1 jsp相关uml图
其中,org.apache.jsp.index_jsp是tomcat将index.jsp转化为servlet源代码后的结果。其代码可以在如下目录中看到(当然,你要首先访问index.jsp才会翻译,编译)
2.2 具体类源代码
2.2.1 JspPage源代码
package javax.servlet.jsp; import javax.servlet.Servlet; public abstract interface JspPage extends Servlet { public abstract void jspInit(); public abstract void jspDestroy(); }
2.2.2 HttpJspPage源代码
package javax.servlet.jsp; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public abstract interface HttpJspPage extends JspPage { public abstract void _jspService(HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse) throws ServletException, IOException; }
2.2.2 HttpJspBase 源代码
和HttpJspPage名称虽然很香精 ,但已经位于不同的包中了。下面的源代码是我从tomcat6中的jasper.jar拉出来的。
package org.apache.jasper.runtime; import java.io.IOException; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.jsp.HttpJspPage; import org.apache.jasper.compiler.Localizer; public abstract class HttpJspBase extends HttpServlet implements HttpJspPage { public final void init(ServletConfig config) throws ServletException { super.init(config); jspInit(); _jspInit(); } public String getServletInfo() { return Localizer.getMessage("jsp.engine.info"); } public final void destroy() { jspDestroy(); _jspDestroy(); } public final void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { _jspService(request, response); } public void jspInit() { } public void _jspInit() { } public void jspDestroy() { } protected void _jspDestroy() { } public abstract void _jspService(HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse) throws ServletException, IOException; }
2.2.2 JspSourceDependent源代码
package org.apache.jasper.runtime; public abstract interface JspSourceDependent { public abstract Object getDependants(); }
2.2.2 org.apache.jsp.index_jsp 源代码
上面提到过org.apache.jsp.index_jsp是tomcat将index.jsp转化为servlet的源代码。
package org.apache.jsp; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; import java.util.*; public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent { private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory(); private static java.util.List _jspx_dependants; private javax.el.ExpressionFactory _el_expressionfactory; private org.apache.AnnotationProcessor _jsp_annotationprocessor; public Object getDependants() { return _jspx_dependants; } public void _jspInit() { _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); _jsp_annotationprocessor = (org.apache.AnnotationProcessor) getServletConfig().getServletContext().getAttribute(org.apache.AnnotationProcessor.class.getName()); } public void _jspDestroy() { } public void _jspService(HttpServletRequest request, HttpServletResponse response) throws java.io.IOException, ServletException { PageContext pageContext = null; HttpSession session = null; ServletContext application = null; ServletConfig config = null; JspWriter out = null; Object page = this; JspWriter _jspx_out = null; PageContext _jspx_page_context = null; try { response.setContentType("text/html;charset=GB18030"); 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'); out.write('\n'); String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; out.write("\r\n"); out.write("\r\n"); out.write("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">\r\n"); out.write("<html>\r\n"); out.write(" <head>\r\n"); out.write(" <base href=\""); out.print(basePath); out.write("\">\r\n"); out.write(" \r\n"); out.write(" <title>My JSP 'index.jsp' starting page</title>\r\n"); out.write("\t<meta http-equiv=\"pragma\" content=\"no-cache\">\r\n"); out.write("\t<meta http-equiv=\"cache-control\" content=\"no-cache\">\r\n"); out.write("\t<meta http-equiv=\"expires\" content=\"0\"> \r\n"); out.write("\t<meta http-equiv=\"keywords\" content=\"keyword1,keyword2,keyword3\">\r\n"); out.write("\t<meta http-equiv=\"description\" content=\"This is my page\">\r\n"); out.write("\t<!--\r\n"); out.write("\t<link rel=\"stylesheet\" type=\"text/css\" href=\"styles.css\">\r\n"); out.write("\t-->\r\n"); out.write(" </head>\r\n"); out.write(" \r\n"); out.write(" <body>\r\n"); out.write(" This is my JSP page. <br>\r\n"); out.write(" </body>\r\n"); out.write("</html>\r\n"); } catch (Throwable t) { if (!(t instanceof SkipPageException)){ out = _jspx_out; if (out != null && out.getBufferSize() != 0) try { out.clearBuffer(); } catch (java.io.IOException e) {} if (_jspx_page_context != null) _jspx_page_context.handlePageException(t); } } finally { _jspxFactory.releasePageContext(_jspx_page_context); } } }
其对应的index.jsp为
<%@ page language="java" import="java.util.*" pageEncoding="GB18030"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <base href="<%=basePath%>"> <title>My JSP 'index.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> </head> <body> This is my JSP page. <br> </body> </html>
2.2.3 九大隐藏对象
从jsp转换的源码中,很容易的就可以发现了传说中的9大jsp内置隐藏对象中的8个。如下:
PageContext pageContext = null; HttpSession session = null; ServletContext application = null; ServletConfig config = null; JspWriter out = null; Object page = this; JspWriter _jspx_out = null; PageContext _jspx_page_context = null;
至于第9个,只有page指令被设置为:
<%@ page isErrorPage="true" %>
才会出现:
Throwable exception = org.apache.jasper.runtime.JspRuntimeLibrary.getThrowable(request);
9大内置对象中,exception几乎不用,其他则是耳熟能详。唯独 PageContext pageContext 少见,我们以后娓娓道来。
参考:《深入体验Java_Web开发内幕-核心基础\》
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