JSP

 1.  Instructions 
      effect ： Used for configuration JSP page , Import resource file 
      Format ：
         <%@  Instruction names   Property name 1= Property value 1  Property name 2= Property value 2 ... %>
      classification ：
         1. page： To configure JSP page 
             contentType： Equate to response.setContentType()
                 1. Set the mime Type and character set 
                 2. Set up current jsp Page code ( Low level tools to set pageEncoding Property before setting the character set )
             errorPage： Automatically jump to the specified error page after sending an exception 
             isErrorPage： Identifies whether the current is an error page 
                 true： yes , You can use built-in objects exception
                 false： The default value is , Can not be 
         
         2. include： The page contains . Import page resource file 
             <%@include file="top.jsp"  %>
         
         3. taglib： Import resources 
             <%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
                 prefix： Prefix , Customize                   

 2.  notes ：
     1. html notes ：
         <!-- --!>: Only comment html code snippet 
     2. jsp notes ：
         <%-- --%>:  Can annotate all 

 3.  Built-in objects ( Interview questions )
      stay jsp There is no need to create , You can use it directly 
      Altogether 9 individual ：
              Variable name           The real type                  effect 
         pageContext         PageContext          The current page shares data , You can also get eight other built-in objects 
         request             HttpServletRequest   One request to access multiple resources ( forward )
         session             HttpSession          Between multiple requests in a session 
         application         ServletContext       All users share data 
         response            HttpServletResponse  The response object 
         page                object               Current page (Servlet) The object of this
         out                 jspwriter            Output object 
         config              ServletConfig       Servlet Configuration objects for 
         exception           throwable            Exception object 

MVC Development mode

 MVC：
     1. M：Model Model . javab
              Complete specific business operations . Such as ： Query the database , Encapsulated object 
     2. V：view View .    JSP 
              Display data 
     3. C：Controller controller . Servlet
              Get user input 
              Call model 
              Give the data to the view for display 
 ​
  Advantages and disadvantages ：
     1.  advantage ：
             1.  Low coupling , Convenient maintenance , It's good for division of labor and cooperation 
             2.  High reusability 
 ​
     2.  shortcoming ：
             1.  Complicate the project architecture , High requirements for developers 
         

EL expression

 1. effect ： Replace and simplify jsp On the page java Code writing 
 2. grammar ：${ expression }
 3. Be careful ：
     jsp The default support el expression . If you want to ignore el expression 
         1. stay page Instruction set isELIgnored="true". Ignore all 
         2. \${ expression }： Ignore individual .
 ​
 4.  Use ：
     1. operation 
          Air transport operator ：empty
              function ： Used to determine string 、 aggregate 、 Whether the array object is null Or the length is 0
             ${empty list}
             ${not empty str}
     
     2. Get value 
         1. el One of the expressions gets the value from the domain object 
         2.  grammar ：
             1. ${ domain name . Key name }： Gets the value of the specified key from the specified field 
                  domain name ：
                     1. pageScope        --> pageContext
                     2. requestScope     --> request
                     3. sessionScope     --> session
                     4. applicationScope --> application（ServletContext）
                 
                      request.setAttribute("name"," Zhang San ");
                      ${requestScope.name}
             2. ${ Key name }： Whether there is a value corresponding to the key in the small to large field         
             3. Get objects 、list aggregate 、map The value of the set 
                 1.  object ：${ domain name . Key name . Property name }
                      Essentially, it calls getter Method 
                 
                 2. List aggregate ：${ domain name . Key name [ Index value ]}
                 
                 3. Map aggregate ：
                     ${ domain name . Key name .key name }
                     ${ domain name . Key name ["key name "]}

     3.  Implicit objects ：
         el There is... In the expression 11 Implicit objects 
         pageContext：
              obtain jsp other 8 Built in objects 
             
             ${pageContext.request.contextPath}： Get virtual directory dynamically 

JSTL

 1. effect ： Used to simplify and replace jsp On the page java Code    
 ​
 2. Use steps 
     1.  Import jar package 
     2.  Import label Library ：taglib Instructions 
     3.  Use a label 
     
 3. Commonly used labels 
     1. if： amount to java Code if sentence 
          attribute ：test It's a must attribute , receive boolean expression 
              Expression for true Show content 
              In general ,test Property values will be combined with el Use expressions together 
          Be careful ：c:if The label doesn't have else situation 
         
     2.choose： amount to java Code switch sentence    
         1.choose label     amount to switch
         2.when label      amount to case
         3.otherwise      amount to default
         
         
     3.foreach： amount to java Code for sentence 

Three layer architecture ： Software design architecture

  Interface layer 
  Business logic layer 
  Data access layer