Javaweb--el Technology, JSTL Technology, Java EE development model

El Technology

El (express lanuage) expression can be embedded inside the JSP page, reduce the writing of JSP script, El appears to replace the JSP page script writing.

El's main function is to extract data from the field, format ${el expression}

• El gets the value in the PageContext domain: ${pagescope.key};
• El obtains the value in the request domain: ${requestscope.key};
• El gets the value in the session field: ${sessionscope.key};
• El gets the value in the application domain: ${applicationscope.key};.
• El obtains a value from four domains ${key};

The same is obtained from the PageContext domain, the request domain, the session field, the application domain, and is not searched backwards after being fetched in a domain

El Built-in (11) Objects

1) receive the parameters of the transmitted

Param and paramvalues//param. Name of the parameter

Equivalent to Request.getparameter () request.getparametervalues ()

2) Get Request header information

Header,headervalues//header. Request Header Parameters

Equivalent to Request.getheader (name)

3) Get Global initialization parameters

Initparam//Initparam. Name of parameter

Equivalent to This.getservletcontext (). Getinitparameter (name)

Web. xml file format

<context-param>    <param-name>abc</param-name>    <param-value> xin brother Bang Bang da! </param-value></context-param>

4) Cookies

Cookies//Cookie.name,cookie.value

Equivalent to Request.getcookies ()---cookie.getname ()---cookie.getvalue ()

5) PageContext

PageContext.request.contextPath//Get the current web app name

Equivalent

<%=pagecontext.getrequest () .getcontextpath%> This code cannot be implemented

Other features: Get the other eight big objects

Pagecontext.request/response/cookie/session

Name	Type	Describe
Out	Javax.servlet.jsp.JspWriter	For page output
Request	Javax.servlet.http.HttpServletRequest	Get user request information,
Response	Javax.servlet.http.HttpServletResponse	Response information from the server to the client
Config	Javax.servlet.ServletConfig	Server configuration, can get initialization parameters
Session	Javax.servlet.http.HttpSession	Information to save the user
Application	Javax.servlet.ServletContext	Shared information for all users
Page	Java.lang.Object	Refers to an instance of the current page-converted Servlet class
PageContext	Javax.servlet.jsp.PageContext	JSP's page container
exception	Java.lang.Throwable	Represents an exception that occurs on a JSP page and does not work in the error page

Determines whether the empty

${empty User}

Jstl Technology

JSTL (JSP standard tag Library), JSP standards tag libraries, can be embedded in the JSP page using the form of tags to complete business logic and other functions. The purpose of the JSTL is to replace the script code in the JSP page, as is the case with El. The JSTL standard standard Tag Library has 5 sub-libraries, but as it develops, it is often the core library core that is used today.

Tag Library	The URI of the tag library	Prefix
Core	Http://java.sun.com/jsp/jstl/core	C
i18n	Http://java.sun.com/jsp/jstl/fmt	Fmt
Sql	Http://java.sun.com/jsp/jstl/sql	Sql
Xml	Http://java.sun.com/jsp/jstl/xml	X
Functions	Http://java.sun.com/jsp/jstl/functions	Fn

A. Download two jar packages for tag library

B. Importing a tag library

<%@ taglib uri= "Http://java.sun.com/jsp/jstl/core" prefix= "C"%>

1. If condition judgment

Format:

<c:if test= "condition judgment" > label

Where test is the condition that returns a Boolean, there is no else in Jstl.

2. For Loop

Format:

<c:forEach> tags

There are two combinations of modes of use:

The first form of

The second form of

<c:foreach items= "${strlist}" var= "str" >${STR}<br/></c:foreach>

Java EE development model

Model in the development process summed up the "routines", summed up a set of conventional design patterns

MVC pattern

M:model---Model JavaBean: encapsulating data
V:view-----View JSP: Simply display the page
C:controller----Controller Servelt: Get data--encapsulate data--pass data--Assign the displayed JSP page

Java EE three layer architecture

Web tier: Interacting with clients

Service layer: Complex business processing

DAO Layer: Interacting with a database

The three-tier architecture is embodied through the package structure in the development practice

Javaweb--el Technology, JSTL Technology, Java EE development model