jsp 是什么 ，jsp 隐式对象

google 搜索 java server page
http://www.oracle.com/technetwork/java/javaee/jsp/index.html http://docs.oracle.com/javaee/5/tutorial/doc/bnagx.html
5. JavaServer Pages Technology

6. JavaServer Pages Documents

7. JavaServer Pages Standard Tag Library

8. Custom Tags in JSP Pages

9. Scripting in JSP Pages

什么是pageContext
http://docs.oracle.com/javaee/5/tutorial/doc/bnahq.html#bnahv

Implicit Objects

The JSP expression language defines a set of implicit objects:

pageContext: The context for the JSP page. Provides access to various objects including:

servletContext: The context for the JSP page’s servlet and any web components contained in the same application. See Accessing the Web Context.

session: The session object for the client. See Maintaining Client State.

request: The request triggering the execution of the JSP page. See Getting Information from Requests.

response: The response returned by the JSP page. See Constructing Responses.

In addition, several implicit objects are available that allow easy access to the following objects:

param: Maps a request parameter name to a single value

paramValues: Maps a request parameter name to an array of values

header: Maps a request header name to a single value

headerValues: Maps a request header name to an array of values

cookie: Maps a cookie name to a single cookie

initParam: Maps a context initialization parameter name to a single value

Finally, there are objects that allow access to the various scoped variables described in Using Scope Objects.

pageScope: Maps page-scoped variable names to their values

requestScope: Maps request-scoped variable names to their values

sessionScope: Maps session-scoped variable names to their values

applicationScope: Maps application-scoped variable names to their values

Scope Object	Class	Accessible From
Web context	javax.servlet.ServletContext	Web components within a web context. See Accessing the Web Context.
Session	javax.servlet.http.HttpSession	Web components handling a request that belongs to the session. See Maintaining Client State.
Request	Subtype ofjavax.servlet.ServletRequest	Web components handling the request.
Page	javax.servlet.jsp.JspContext	The JSP page that creates the object. See Using Implicit Objects.