JSP fourth week
A JSP Overview
meaning:
Java Server Pages, one of the widely used server-side scripting language; (running on the server side BS structure )
JSP code executed by the server-side JSP engine, and the results in HTML pages sent to the client forms.
JSP page: use the program document prepared by the JSP (extension .jsp).
JSP pages mainly by conventional HTML code and embedded therein Java code. ( Dynamically generated page content)
in a JSP page, may include: HTML code, CSS codes, JavaScript code embedded Java code, instruction identification, operation identification, comments and so on.
Two JSP operating principle
1. Web browser sends a request to a page ---> to determine whether the JSP page request (page request is an HTML page: page code directly to the request back to the Web browser)
---> Request a JSP page (JSP engine checks whether the request for the first time)
---> ① first request : JSP engine JSP pages on this code into the code Servlet (.java), and then generates a byte code (.class) file to be compiled and executed
---> ② is not the first request and has not been modified : JSP engine calls JVM execution has been compiled bytecode files (without recompiling)
----> and perform results to Web browser display
Three script logo
classification:
(1) JSP expression:
Syntax: <% = expression%>
Expression: Java language can be any expression, with the ultimate result will be converted to a string to be output
（2）
① claims identities (life cycle starting from the creation to the server closed end)
Meaning: a globally defined variables or methods in JSP pages (JSP page can be accessed throughout)
Syntax: <code% declare a variable or method%!>
<!%
Int NUM = 0; // global variable
int Check () { // global method
NUM ++ ;
return NUM;
}
%>
② snippet (life cycle is created from the beginning to the page is closed, after closing will be destroyed)
Meaning: JSP pages embedded Java code or script code (page during processing of the request is performed).
By Java code can define a variable flow control statements or the like;
by script code JSP built-in objects can be applied to the output content on a page, requests and responses, and so access session.
Syntax:
<% the Java code or script code%>
(3) script
Four page instruction
1. Meaning: specify the relevant properties for the entire JSP page
2. syntax: <% @ 1 Page attribute name = "attribute value 1" 2 attribute name = "attribute value 2" ...%>
3. Common attributes:
(1) language attribute
is used to specify the language used in the JSP page, currently only supports Java language.
例如：
<%@ page language="java"%>
(2) import property
is used to specify packet class to import JSP page (page for embedded Java code or calls).
例如：
<%@ page import="java.util.Date" %>
(3) session attribute
to specify whether JSP pages using HTTP session (session) objects. The default value is true.
For example:
<% @ = the session Page "to false"%>
(. 4) the pageEncoding attribute
specifies the JSP page encoding format, document encoding (character set). To support Chinese, generally set the property GBK or UTF-8.
For example:
<% @ Page the pageEncoding = "UTF-. 8"%>
(. 5) contentType attribute
specifies the JSP page MIME type and character encoding, the client browser will display the web page content based on the attribute.
例如：
<%@ page contentType = "text/html; charset=utf-8"%>
......
五 包含指令
1.