简简单单---- (一) jsp简介

最新推荐文章于 2024-09-20 20:21:24 发布

iteye_11788

最新推荐文章于 2024-09-20 20:21:24 发布

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文章标签： runtime java

JSP(java server page):

本质就是把java代码嵌套到html中，然后经过jsp容器的编译执行，再根据这些动态代码运行的结果生成对应的html代码。从而可以从客户端浏览器中中正常显示。

JSP运行原理：

当JSP页面第一次被请求运行时，服务器的jsp编译器会生成jsp页面对应的java代码，并且编译成类文件。当服务器再次收到对这个jsp也卖弄请求的时候，会判断这个jsp页面是否被修改过，如果被修改过就会重新生成java代码并重新编译，而且服务器中的垃圾回收方法会自动把没有的类文件删除。

看我们这个jsp执行的过程：

test.jsp:

<%@ page language="java" contentType="text/html; charset=GB18030"
    pageEncoding="GB18030"%>
<!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=GB18030">
<title>jsp示例</title>
</head>
<body>
	jsp示例,jsp运行过程~~~
</body>
</html>

我们新建了一个test.jsp文件，在安装好JDK和jsp文件的运行“容器”tomcat后，我们启动tomcat，在浏览器中输入我们test。jsp文件的地址，http://localhost:8080/test/test.jsp的时候，我们打开我们的网页，可以看到我们运行的结果。同时我们在tomcat的文件中，D:\tomcat\apache-tomcat-7.0.39\work\Catalina\localhost\test\org\apache\jsp 文件夹下可以看到两个文件，一个是。class一个是。java的文件。

这就是我们的test.jsp对应的java代码，和被java虚拟机编译了的 .class文件。

我们打开这个java文件，代码如下：

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/7.0.39
 * Generated at: 2013-10-03 08:15:24 UTC
 * Note: The last modified time of this file was set to
 *       the last modified time of the source file after
 *       generation to assist with modification tracking.
 */
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 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=GB18030");
      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("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=GB18030\">\r\n");
      out.write("<title>jsp示例</title>\r\n");
      out.write("</head>\r\n");
      out.write("<body>\r\n");
      out.write("\tjsp示例,jsp运行过程~~~\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);
    }
  }
}