JSP内部对象详解

JSP内部对象详解
1.1 application
*在jsp中获得application对象
如：getServletContext().setAttribute("counter",new mycount.Counter());
如：<jsp:useBean scope="application" id="counter" class="mycounter.Counter"/>
*在jsp中处理On Application Start和On Session Start事件的方法
使用HttpSessionBindingListener类.
添加session:
session.putValue("bingdings.listener",new MyListener(getServletContext());
定义MyListener类：
import javax.servlet.http.*;
import javax.servlet.*;
public class MyListener implements HttpSessionBindingListener{
ServletContext context;
public MyListener(ServletContext context){
this.context=context;
}
public void valueBound(HttpSessionBindingEvent event){
System.out.println("valuebound:someone just bound my listener to a session!");
}
public void valueUnbound(HttpSessionBindingEvent event){
System.out.println("valueunbound:someone just unbound my listener!");
}
}

1.2 request
*获取一个正在运行时的jsp/servlet文件的绝对url地址

Stringf file=request.getRequestURL();
if(requet.getQueryString()!=null{
file+='?'+request.getqueryString();
}
URL reconstructedURL=new URL(request.getScheme(),request.getServerName(),request.getServerPort(),file);
out.println(reconstructedURL.toString());
*获取客户端通过哪一个url访问本页面
String callPage=request.getHeader("Referer");
*获取当前脚本在当疥文件系统中的真实路径
request.getRealPath(request.getServletPath());
*判断多个submit中的一个
<input type=submit name="sub" value="up">
<input type=submit name="sub" value="down">
在jsp中使用request.getParameter("sub");就可分辨

1.3 response
*网页重定向之三方法
(1)response.sendRedirect(url);
(2)<％response.setStatus(HttpServletResponse.SC_MOVED_PREMANENTLY);
String nowloc="/newpath/index.htm";
response.setHeader("Location",newloc);％>
(3)<jsp:forward page="/newpage.jsp"/>
注意上法只能在任何输出还没有发送到客户端之前使用这种方法
*禁用缓存
<％response.setHeader("Cache-Control","no-store");
response.setDateHeader("Expires",0);％>

1.4 session
*存活时间
<％session.setMaxInactiveInterval(300);％>
*注销
session.invalidate();

1.5 exception
*在jsp页面中处理Servlet的错误
protected void sendErrorRedirect(HttpServletRequest request,
HttpServletResponse response,String errorPageURL,Throwable e)
throws ServletException,IOException{
request.setAttibute("javax.servlet.jsp.jspException",e);
getServletConfig().getServletContext();
getRequestDispatcher(errorPageURL).forward(request,response);
}
public void doPost(HttpServletRequest request,HttpServletResponse response){
try{
//
}
catch(Exception e){try{
sendErrorRedirect(request,response,"/jsp/ErrPage.jsp",e);
}catch(Exception e){e.printStackTrace();}
}
}
*在jsp页面中输出错误的stacktrace
(1)
<％@ page isErrorPage="true％>
<％
out.println("<pre>");
printWriter pw=response.getWriter();
exception.printStackTrace(pw);
out.println("</pre>");
％>
(2)
<％@ page isErrorPage="true％>
<pre>
<％
exception.printStackTrace(new PrintWriter(out));
％>
</pre>

1.6 Cookie
*设置cookie
<％
Cookie mycookie=new Cookie("aName","aValue");
response.addCookie(mycookie);
//mycookie.setMaxAge(time);
％>