Web开发3：Tomcat根据JSP生成Servlet机制深度剖析及核心源代码详解
1：什么是JSP(Java Server Pages)：在传统的HTML页面中加入JAVA程序片段和JSP标签，就构成JSP网页。
JAVA程序片段可以操纵数据库，重定向网页以及发送Email等，实现建立动态网页所需要的功能。
所有程序操作都在服务器端执行，网络上传送给客户端的仅是得到的服务器的结果，这样大大降低了对客户浏览器的要求，
即使客户浏览器不支持JAVA，也可以访问JSP页面。
JSP的文件结构及主要标签：
在Tomcat的work\Catalina\localhost\目录下，存在许多由JSP文件生成的JAVA及CLASS文件。如下图。
以下是login.jsp文件生成的JAVA代码文件
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import java.util.*;
public final class login_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=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("<html>\r\n");
out.write("<body>\r\n");
out.write(" <form action=\"/servletTest/login\" method=\"get\">\r\n");
out.write(" \tusername:<input type=\"text\" name=\"username\"></input><br>\r\n");
out.write(" \tpassword:<input type=\"password\" name=\"password\"></input><br>\r\n");
out.write(" \t<input type=\"submit\" value=\"提交\"></input> \r\n");
out.write(" \t<input type=\"reset\" name=\"重置\"></input>\r\n");
out.write(" </form>\r\n");
out.write("</body>\r\n");
out.write("</html>\r\n");
out.write("\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);
}
}
}
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