JSP入门的简单学习
我的第一个JSP文件是非常简单的JSP,如下:
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<%@page import="java.util.Date"%> <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>JSP</title> </head> <body> <%="hello" %> </body> </html> |
我使用的是Tomcat7.0服务器,加载到Eclipse后,会编译我上面的JSP文件,把该JSP文件通过编译器编译成一个
Servlet的java文件,如下图:
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package org.apache.jsp; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; import java.util.Date; 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 javax.el.ExpressionFactory _el_expressionfactory; private org.apache.tomcat.InstanceManager _jsp_instancemanager;
public java.util.Map<java.lang.String,java.lang.Long> getDependants() { return _jspx_dependants; }
public void _jspInit() { _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig()); }
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("<!DOCTYPE html>\r\n"); out.write("<html>\r\n"); out.write("<head>\r\n"); out.write("<meta charset=\"UTF-8\">\r\n"); out.write("<title>JSP</title>\r\n"); out.write("</head>\r\n"); out.write("<body>\r\n"); out.print("hello" ); out.write("\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 { 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); } } } |
可以看出,JSP文件确实在后台服务器中被编译成一个java文件,我们只关注我们在JSP页面中写入的内容,而对html标签的解析我们不去关注
//JSP文件会被jsp文件名会被编译成以index_jsp命名的类(我的jsp文件名为index.jsp)
public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
//通过工厂模式来产生一个JSP文件的的解析器
private static final javax.servlet.jsp.JspFactory _jspxFactory =
javax.servlet.jsp.JspFactory.getDefaultFactory();
//调用初始化方法通过全局上下文来获取JSP参数
public void _jspInit() {
_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
_jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
}
//编译完成后会销毁该线程
public void _jspDestroy() {
}
//这里是核心,是对JSP文件的完整解析
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;
//这里是解析后的内容
out.write("\r\n");
out.write("\r\n");
out.write("<!DOCTYPE html>\r\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write("<meta charset=\"UTF-8\">\r\n");
out.write("<title>JSP</title>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.print("hello" );
out.write("\r\n");
out.write("</body>\r\n");
out.write("</html>");
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