JSP脚本中的九大内置对象详解(上)

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原理:我们都知道，jsp在第一次被请求时会被编译成servlet，实际上是由该servlet来处理用户请求。

了解了上述内容，我们再来说说九大内置对象的实质。它们都是Servlet API中接口的实例，在jsp编译成servlet时进行了默认初始化，所以我们才能在jsp脚本中直接使用它们。

直接上代码:

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=GBK");
pageContext = _jspxFactory.getPageContext(this, request, response,
"error.jsp", 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("\r\n");
out.write("<!doctype html>\r\n");
out.write("<html>\r\n");
out.write("\t<head>\r\n");
out.write("\t\t<title>webDEMO欢迎您</title>\r\n");
out.write("\t</head>\r\n");
out.write("\t<body>\r\n");
out.write("\t\t");
out.write("\r\n");
out.write("\t\t");
out.write("\r\n");
out.write("\t\t\r\n");
out.write("\t\twebDEMO欢迎您");
new Date();//从这里可以看出，jsp脚本中的内容会编译进该处理方法中
out.write(" ");
out.print((++count) );
out.write(" ");
out.print(info() );
out.write(" ");
out.print(getServletInfo() );
out.write("\r\n");
out.write("\t\t");

String name = config.getInitParameter("name");//int a=1/0;

out.write("\r\n");
out.write("\t\t");
out.print(name );
out.write("\r\n");
out.write("\t</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);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}