JSP-JSP的生命周期

最新推荐文章于 2020-07-31 00:34:31 发布

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最新推荐文章于 2020-07-31 00:34:31 发布

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分类专栏： J2EE

本文链接：https://blog.youkuaiyun.com/mascf/article/details/51348159

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JSP全称Java Server Pages，是一种动态网页开发技术。跟我们学习ASP.NET的时候的前台是一样的。

Servlet也可一种做页面的输出，但是这么做很不方便，需要做大量的页面拼接，开发效率很低。所以，Sun公司就推出了JSP，来方便前台页面的开发。

JSP的生命周期

其实JSP就是Servlet，在我们第一次访问JSP页面的时候，会将JSP页面编译成Servlet放在Tomcat\work目录中。

下面看一下JSP代码

<%@ 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>

<title>JSP</title>
</head>
<body>
	<%
		int a=10;
	%>
	a=<%=a%>
</body>
</html>

然后看一下编译生成的Servlet

package org.apache.jsp;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;

public final class test_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("<!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("\r\n");
      out.write("<title>JSP</title>\r\n");
      out.write("</head>\r\n");
      out.write("<body>\r\n");
      out.write("\t");

		int a=10;
	
      out.write("\r\n");
      out.write("\ta=");
      out.print(a);
      out.write("\r\n");
      out.write("</body>\r\n");
      out.write("</html>");
    } 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);
        else log(t.getMessage(), t);
      }
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

所以，JSP其实也是拼接出来生成Servlet代码，只是这个工作编译器帮我们做了而已。

下面用一张图来表示下