【Java.Web】JSP —— 语法基础 —— 隐式对象implicit Objects

隐含对象 - Implicit Objects

在JSP程序片段中，包含如下隐含对象，每个对象都被固定的引用变量引用。JSP不需要做任何变量声明，就可以直接通过固定的引用变量来引用这些对象。

request

具体的类型取决于使用的协议类型，为javax.servlet.ServletRequest的子类，i.e.

javax.servlet.http.HttpServletRequest

Scope：request

response

具体的类型取决于使用的协议类型，为javax.servlet.ServletResponse的子类，i.e.

javax.servlet.http.HttpServletResponse

Scope：response

pageContext

javax.servlet.jsp.PageContext

page context for this JSP page.

Scope：page

application

javax.servlet.ServletContext

servlet context obtained from the servlet configuration object(as in the call: getServletConfig().getContext() ).

Scope：application

out

javax.servlet.jsp.JspWriter

an object that writes into the output scream.

Scope：page

config

javax.servlet.ServletConfig

The ServletConfig for this JSP page.

Scope：page

page

java.lang.Object

The instance of this page's implementation class processing the current request.

page对象是this的同义词

Scope：page

session

javax.servlet.http.HttpSession

The session object created for the requesting client. This variable is only valid for HTTP protocols

Scope：session

exception

java.lang.Throwable

The uncaught Throwable that resulted in the error page being invoked.

Scope：page

示例

示例1：

<%
    String username = request.getParameter("username");
    out.print(username);
%>

<%
    String username = request.getParameter("username");
%>
<%= username %>

在上面的两段代码中，是等价的，都用于向页面打印username。

示例2：

再例如通过ServletContext隐含对象向Web应用范围内存放一个username属性，

<% application.setAttribute("username", "myName"); %>