Introduction to Jsp Technology

1.jsp scripts and comments

　　jsp script

　　　　1) <%java code%> -------- The internal java code is translated to the internal of the server method

　　　　2) <%= java variable expression %> ---- will be translated into server internal out.print()

　　　　3) <%! java code%>-- will be translated into the content of the members of the servlet

　　jsp comments

　　　　1) Html comment <!--comment content--> ------- visible scope jsp source code, translated servlet, page

　　　　2) java comment//single-line comment/*multi-line comment*/ -- visible range jsp source code translated servlet

　　　　3) jsp comment <%--comment content--%>---visible scope jsp source code is visible

2. JSP operation principle -- the essence of JSP is servlet

　　The first time the jsp is accessed / the file is modified, it will be translated into a servlet by the web container and executed (in the servlet in the work folder of the Tconcat server)

　　Process:

　　　　　　The first access/file is modified--->helloServlet.jsp -->helloServlet_.java->compile and run

3.jsp instruction

1. page command --- the command with the most attributes (the page command defaults in actual development)

   An instruction with the most attributes, according to different attributes, guide the characteristics of the entire page

   Format: <%@ page attribute name 1= "attribute value 1" attribute name 2= "attribute value 2" ...%>

   Common properties are as follows:

   language: the kinds of languages ​​that can be embedded in the jsp script

   pageEncoding: the encoding of the current jsp file---it can contain contentType

   contentType：response.setContentType(text/html;charset=UTF-8)

   session: whether jsp automatically creates a session during translation

   import: package that imports java

   errorPage: which page to jump to when the current page has an error

   isErrorPage: the current page is an error-handling page

2. include directive

   Page includes (static include) directive, which can include one jsp page into another jsp page

   Format: <%@ include file="Address of included file"%>

3. taglib directive

   Introduce tag library (jstl tag library, struts2 tag library) into jsp page

   Format: <%@ taglib uri="tag library address" prefix="prefix"%>

4.jsp built-in/implicit objects (9)

　　

There is also an exception, error handling

name	Types of	describe
out	javax.servlet.jsp.JspWriter	for page output
request	javax.servlet.http.HttpServletRequest	Get user request information,
response	javax.servlet.http.HttpServletResponse	Response message from server to client
config	javax.servlet.ServletConfig	Server configuration, you can get initialization parameters
session	javax.servlet.http.HttpSession	Used to store user information
application	javax.servlet.ServletContext	Shared information for all users
page	java.lang.Object	Refers to the instance of the Servlet class after the conversion of the current page
pageContext	javax.servlet.jsp.PageContext	JSP page container
exception	java.lang.Throwable	Indicates the exception that occurs in the JSP page, and only works in the error page

　　1) The type of out object
       　　　　out is jspWriter

　　　　　　The function is to output the content of the customer service terminal---->out.write();

　　　　　   The default buffer of out is 8kb, which can be set to 0-->-buffer=“0kb”, and directly write to the response buffer after closing

　　2) pageContext object (small important)

　　　　1. The role and nature of the pageContext object

　　　　　　The context object of the jsp page, the role is as follows

　　　　　　The page object is not the same thing as the pageContext object

　　　　　　pageContext is a domain object

　　　　2. Common methods of pageContext object

　　　　   1. Access data

　　　　　　setAttribute(String name,Object obj)

　　　　　　getAttribute(String name)

　　　　　　removeAttrbute(String name)

　　　　　　write/read data to other domains　　

　　　　　　setAttribute(String name,Object obj,int scope)

　　　　　　getAttribute(String name,int scope)

　　　　　　removeAttrbute(String name,int scope)

　　　　　　findAttribute(String name)

　　　　　　------- Find the data of the name in all domains, return if found, no longer search, domains from small to large

　　　　　　-------The pageContext domain->request domain->session domain->application domain in turn

　　　　2.pageContext can get other 8 implicit objects

　　　　　　　　Encapsulation for passing parameters

　　　　　　　　Calling example:

　　　　　　　　　　pageContext.getRequest()

　　　　　　　　　　pageContext.getSession()

5.jsp tag (action)

　　　　1. Page includes (dynamic include): <jsp:include page="included page">

　　　　2. Request forwarding <jsp:forward page="Resources to be forwarded">

What is the difference between static and dynamic include?

　　　　The static page file is two files translated into one and the dynamic page file is two translated or two people