jsp (五) <jsp:useBean> scope

1、

<jsp:useBean scope="page" id="aa" class="com.gc.Bean"/>   aa表示一个局部变量

翻译：Bean aa=  new Bean();

2、

<jsp:useBean scope="request" id="aa" class="com.gc.Bean"/>  aa在一个request时有效  

<jsp:forward page="requestforward.jsp">  一个request

response.sendRedirect("request.jsp") 二个request

翻译:

Bean aa = (Bean) request,getAttribute("aa");

if (aa == null) {

aa = new Bean;

request.setAttribute("aa",aa);

}

3、<jsp:useBean scope="session" id="aa" class="com.gc.Bean"/>   aa在session时有效

翻译:

Bean aa = (Bean) session.getAttribute("aa");

if (aa==null) {

aa = new Bean();

session.setAttribute("aa",aa);

}  

4、 <jsp: scope="application" id="aa" class="com.gc.Bean"/>  aa在整个web app上有效

Bean aa = (Bean) application.getAttribute("aa");

if (aa==null) {

aa = new Bean();

application.setAttribute("aa",aa);

}