JSP学习（1）------为何jsp是servlet？

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1.jsp基本介绍

（1）jsp解释

JSP全称是Java Server Pages，它和servle技术一样，都是SUN公司定义的一种用于开发动态web资源的技术。JSP/Servlet规范。JSP实际上就是Servlet。

（2）jsp的执行过程

通常jsp要经历“翻译--------编译”过程，翻译将jsp页面变成.java文件，编译将.java文件变成.class文件。

图解为下面所示：

下面以一个单的例子测试：

<%@page import="java.util.Date"%><%@ 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>Insert title here</title></head><body><%Date date=new Date();out.print(date.toLocaleString()); %></body></html>

部署成功后，在下面路径：D:\javatool\apache-tomcat-7.0.75\work\Catalina\localhost\ee12_jsp\org\apache\jsp得到

（3）对翻译的jsp页面解读

在_1_jsp.java页面中有下面代码（只保留了部分代码）

public final class _1_jsp extends org.apache.jasper.runtime.HttpJspBase    implements org.apache.jasper.runtime.JspSourceDependent {    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 {      out.write("\r\n");      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>Insert title here</title>\r\n");      out.write("</head>\r\n");      out.write("<body>\r\n");      out.write("\t");Date date=new Date();out.print(date.toLocaleString());       out.write("\r\n");      out.write("</body>\r\n");      out.write("</html>");    }   }}

①可以看 _1_jsp extends org.apache.jasper.runtime.HttpJspBase，表示其继承了HttpJspBase类，往下看HttpJspBase的源码

public abstract class HttpJspBase extends HttpServlet implements HttpJspPage {        private static final long serialVersionUID = 1L;    protected HttpJspBase() {    }    @Override    public final void init(ServletConfig config)         throws ServletException     {        super.init(config);        jspInit();        _jspInit();    }        @Override    public String getServletInfo() {        return Localizer.getMessage("jsp.engine.info");    }    @Override    public final void destroy() {        jspDestroy();        _jspDestroy();    }    /**     * Entry point into service.     */    @Override    public final void service(HttpServletRequest request, HttpServletResponse response)         throws ServletException, IOException     {        _jspService(request, response);    }        @Override    public void jspInit() {    }    public void _jspInit() {    }    @Override    public void jspDestroy() {    }    protected void _jspDestroy() {    }    @Override    public abstract void _jspService(HttpServletRequest request,                                      HttpServletResponse response)         throws ServletException, IOException;}

综上可以得到_1_jsp.java继承了HttpServlet，故可以说JSP就是Servlet。

②jsp页面的html元素最终以out.write("<html>");的形式输出。

③在_1_jsp.java的代码中，同样有servlet有的init、serve、destroy等方法。

2.总结：

以上便是对于jsp的初步学习，如果有错误，请告知，谢谢！

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