JSP的九大内置对象和四个作用域
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JSP的九大内置对象： page,application,session,request,response,out,exception,config,pageContext. JSP的四个作用域：application,session,request,page.
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//附上jsp转换成servlet后的java代码package org.apache.jsp;import javax.servlet.*;import javax.servlet.http.*;import javax.servlet.jsp.*;import java.util.*;public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent { int count = 0; int getCount(){ int num = 100; return num = 100*count; } 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 { 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‘); out.write(‘\n‘);String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; out.write("\r\n"); out.write("\r\n"); out.write("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">\r\n"); out.write("<html>\r\n"); out.write(" <head>\r\n"); out.write(" <base href=\""); out.print(basePath); out.write("\">\r\n"); out.write(" \r\n"); out.write(" <title>My JSP ‘index.jsp‘ starting page</title>\r\n"); out.write("\t<meta http-equiv=\"pragma\" content=\"no-cache\">\r\n"); out.write("\t<meta http-equiv=\"cache-control\" content=\"no-cache\">\r\n"); out.write("\t<meta http-equiv=\"expires\" content=\"0\"> \r\n"); out.write("\t<meta http-equiv=\"keywords\" content=\"keyword1,keyword2,keyword3\">\r\n"); out.write("\t<meta http-equiv=\"description\" content=\"This is my page\">\r\n"); out.write(" </head>\r\n"); out.write(" \r\n"); out.write(" <body>\r\n"); out.write(" "); out.write("\r\n"); out.write(" \r\n"); out.write(" "); out.write("\r\n"); out.write(" \r\n"); out.write(" "); out.print(++count ); out.write("\r\n"); out.write(" "); out.print( getCount() ); out.write("\r\n"); out.write(" <form action=\"test.do\" method=\"post\">\r\n"); out.write(" <select name =\"color\">\r\n"); out.write(" <option>White</option>\r\n"); out.write(" <option>Red</option>\r\n"); out.write(" <option>Yellow</option>\r\n"); out.write(" <option>Blue</option>\r\n"); out.write(" </select>\r\n"); out.write(" \r\n"); out.write(" <input type=\"checkbox\" name=\"hobby\" value=\"football\">football<br>\r\n"); out.write(" <input type=\"checkbox\" name=\"hobby\" value=\"football\">basketball<br>\r\n"); out.write(" <input type=\"checkbox\" name=\"hobby\" value=\"football\">baseball<br>\r\n"); out.write(" \r\n"); out.write(" <input type=\"submit\">\r\n"); out.write(" </form>\r\n"); out.write(" </body>\r\n"); out.write("</html>\r\n"); } 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); } } finally { _jspxFactory.releasePageContext(_jspx_page_context); } }} |
application作用域就是服务器启动到关闭的整段时间，在这个作用域内设置的信息可以被所有应用程序使用。application作用域上的信息传递是通过ServletContext实现的.
session作用域比较容易理解，同一浏览器对服务器进行多次访问，在这多次访问之间传递信息，就是session作用域的体现,
一个HTTP请求的处理可能需要多个Servlet合作，而这几个Servlet之间可以通过某种方式传递信息，但这个信息在请求结束后就无效了。Servlet之间的信息共享是通过HttpServletRequest接口的两个方法来实现的。
page对象的作用范围仅限于用户请求的当前页面，对于page对象的引用将在响应返回给客户端之后被释放，或者在请求被转发到其他地方后被释放。对page对象的引用通常存储在pageContext对象中。
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