JSP学习（1）------为何jsp是servlet？

我会带着你远行 2022-06-17 00:24 184阅读 0赞

## 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：

![Center][]

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

![Center 1][]

（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！

[Center]: /images/20220617/ba0345772e454d609796319a24657fec.png
[Center 1]: /images/20220617/62bb4265d91042699c103d4332d4fe4b.png