JSP series: (3) JSP advanced-Nine large built-in objects and four domain objects

1, JSP nine large built-in objects

1.1. What is a built-in object?

In JSP development, a number of objects, such as HttpSession, ServletContext, ServletContext, Httpservletrequet, are frequently used. It is cumbersome to create these objects every time we want to use them. So when Sun design jsp, when the JSP page is loaded, it will automatically help developers to create these objects, and developers only need to directly use these objects call methods, these created objects called built-in objects !!!!

1.2, 9 large built-in objects

9 Large built-in objects

Serial Number	built-in object name	type
1	Request	HttpServletRequest
2	Response	HttpServletResponse
3	Config	ServletConfig
4	Application	ServletContext
5	Session	HttpSession
6	exception	Throwable
7	Page	Object (This)
8	Out	JspWriter
9	PageContext	PageContext

1.3. Out Object

Out object type, JspWriter type, equivalent to PrintWriter with cache

Compare JspWriter and PrintWriter:

Printwriter:wrier (content): write content directly to the browser.

Jspwriter:writer (content): Write content to the JSP buffer

When one of the following conditions is met, the buffer contents are written out:

1) The buffer is full.

2) Refresh Buffer

3) Close the buffer

4) Completed JSP page

1.4. PageContext Object

The type of the PageContext object is PageContext, which is called the JSP context object

1) Eight additional built-in objects can be obtained

The PageContext class provides a series of getxxx methods to get the 7 built-in objects of a JSP

In addition, PageContext inherits from the Jspcontext class, and the Jspcontext class provides a getout () method for obtaining an Out object.

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Usage scenarios: When customizing labels, PageContext objects are used frequently!!! If a method takes the PageContext object as an incoming parameter, the other 8 JSP built-in objects can be indirectly obtained through the PageContext object.

2) itself is a domain object

Function: Save data and get data for sharing data

# Save Data

(1) By default, save to Page field: Pagecontext.setattribute ("name");

(2) data can be saved to four domain objects: Pagecontext.setattribute ("name", domain-wide constant)

# Get Data

(1) By default, gets from the page domain: Pagecontext.getattribute ("name")

(2) data can be obtained from four domains: Pagecontext.getattribute ("name", domain-wide constant)

Domain-wide constants:

Pagecontext.page_scope

Pagecontext.request_scope

PageContext. Session_scope

Pagecontext.application_scope

(3) Automatically search for data in four domains: Pagecontext.findattribute ("name");

Order: page domain, request domain, session domain-> context domain (application domain)

<%@ page language= "java"  import= "java.util.*"  pageencoding= "Utf-8"%><! doctype html public  "-//w3c//dtd html 4.01 transitional//en" >

2. Four domain objects in a JSP
 
 

  
  

    four domain objects in a JSP 
  
  
  
 
   
 
    
Serial Number
 
    
domain object name
 
    
type
 
    
Domain
 
    
Notes
 
   
 
  
  
  
 
   
 
    
1
 
    
PageContext
 
    
PageContext
 
    
Page field
 
    
Learning in JSP
 
   
 
   
 
    
2
 
    
Request
 
    
HttpServletRequest
 
    
Request Domain
 
    
Learning from the servlet
 
   
 
   
 
    
3
 
    
Session
 
    
HttpSession
 
    
Session field
 
    
Learning from the servlet
 
   
 
   
 
    
4
 
    
Application
 
    
ServletContext
 
    
Context Domain
 
    
Learning from the servlet
 
   
 
  
 
 
(There are 3 domain objects in the servlet, and 4 domain objects in the JSP.) )
1) The role of domain objects : Saving data and acquiring data for data sharing.
2) Domain object method :
SetAttribute ("name", Object) to save data
GetAttribute ("name") Gets the data
RemoveAttribute ("name") clears the data
3) domain object scope:
Page field: Can only be used in the current JSP page (current page)
Request domain: Can only be used in the same request (forward)
Session field: Can only be used in the same session (the Session object) (private)
Context domain: can only be used in the same web app. (global)

3. Best practices for JSP
Servlet Technology: Developing dynamic resources. Is a Java class that is best at writing Java code .
JSP Technology: Developing dynamic resources. The Java code is best at outputting html code .

logic is involved in a Web project :
1) Receive Parameters-->servlet do
2) Process business logic, return results-->servlet do
3) Show data to browser-->jsp do
4) Jump to other pages-->servlet do

servlet+jsp mode
servlet:
1) Receive parameters
2) Process business logic
3) Save the results to the domain object
4) Jump to JSP page
Jsp:
1) Extracting data from a domain object
2) display the data to the browser


JSP series: (3) JSP advanced-Nine large built-in objects and four domain objects