JSP's nine built-in objects and four scopes (detailed)

JSP Four scopes:
Page: The current page, that is, just jump to another page will not be valid
Request: A conversation, simple understanding is a request within the scope of the effective
Session: Browser process, as long as the current page is not closed (not enforced by the program), no matter how the jump is valid
Application: Server, as long as the server does not reboot (not forced to clear by the program), the data is valid

Built-in object features:

1. Provided by the JSP specification without the writer's instantiation.

2. Implementing and managing through Web containers

3. All JSP pages can be used

4. Use only in expressions or snippets of script elements (<%= uses built-in objects%> or <% to use built-in objects%>)

Nine commonly used built-in objects:

1. Output input object: Request object, Response object, out object

2. Communication Control object: PageContext object, Session object, Application object

3. Servlet object: Page object, config object

4. Error Handling object: Exception object

Object Common Method Description:

1.out objects (data flow javax.servlet.jsp.jspWriter)

Method name	Description
Print or println	Output data
NewLine	Output line-Wrapping characters
Flush	Output buffer Data
Close	Turn off the output stream
Clear	Clears the data in the buffer but does not output to the client
Clearbuffer	Clears the data in the buffer and outputs it to the client
GetBufferSize	Get buffer size
Getremaining	Get the space in the buffer that is not occupied
Isautoflush	is automatic output

2.request Object (Request information Javax.servlet.http.HttpServletrequest)

Method name	Description
IsUserInRole	Determine if the authenticated user belongs to a member group
GetAttribute	Gets the value of the specified property, such as if the property value does not exist, returns null
Getattributenames	Gets a collection of all property names
GetCookies	Get all Cookie objects
Getcharacterencoding	Gets the character encoding of the request
Getcontentlength	Returns the length of the request body, such as an indeterminate return of-1
GetHeader	Gets the specified name header value
Getheaders	Gets all the values of the specified name header, an enumeration
Getheadernames	Gets the names of all headers, an enumeration
getInputStream	Returns the request input stream, gets the data in the request
GetMethod	Get the method that the client transmits data to the server side
GetParameter	Gets the specified name parameter value
Getparameternames	Gets the name of all parameters, an enumeration
Getparametervalues	Gets all values for the specified name parameter
Getprotocol	Gets the protocol name that the client transmits data to the server side
GetQueryString	Gets the query string sent to the server as a Get method
Getrequesturi	Gets the client address that issued the request string
Getremoteaddr	Get the IP address of the client
Getremotehost	Get the name of the client
GetSession	To get and request related sessions
getServerName	Get the name of the server
Getserverpath	Get the path to the client request file
Getserverport	Get the port number of the server
RemoveAttribute	Delete a property in the request
SetAttribute	Set the specified name parameter value

3.response Object (Response Javax.servlet.http.HttpServletResponse)

Method name	Description
Addcookie	Add a Cookie Object
AddHeader	Add HTTP file Specify name header information
Containsheader	Determines whether the specified name HTTP file header information exists
Encodeurl	Using the SessionID package URL
Flushbuffer	Forces the current buffer content to be sent to the client
GetBufferSize	return buffer size
Getoutputstream	The output stream object returned to the client
Senderror	Sending an error message to the client
Sendredirect	To send a response to another location for processing
setContentType	Set the MIME type of the response
SetHeader	Sets the HTTP file header information for the specified name

4.session Object (Session javax.servlet.http.HttpSession)

Method name	Description
getattribute	Get the property of the specified name
Getattributenames	Get all the names of the properties in the session, an enumeration
GetCreationTime	Return session creation time
GetId td>	Get session identifier
Getlastaccessedtime	Return the last time the request was sent
Getmaxinactiveinterval	Return Session object Lifetime Unit 1 per thousand second
Invalidate	To destroy the Session object
IsNew	Whether each request produces a new Session object
RemoveAttribute	Remove properties for the specified name
setattribute	Set the property value of the specified name

5.pageContext Object (page context Javax.servlet.jsp.PageContext)

Method name	Description
Forward	Redirect to another page or servlet component
GetAttribute	Gets the property value of a specified name in a range
Findattribute	Search for properties of a specified name by range
RemoveAttribute	Deletes the property of a specified name in a range
SetAttribute	Sets the property value of a specified name in a range
GetException	Returns the current exception object
Getrequest	Returns the current Request object
GetResponse	Returns the current Response object
Getservletconfig	Returns the ServletConfig object for the current page
Getservletcontext	Returns the ServletContext object for all page shares
GetSession	Returns the session object for the current page

6.application Objects (Application Javax.servlet.ServletContext)

Method name	Description
GetAttribute	Gets the property value of the specified name in the Application object
Getattributenames	Gets the names of all the properties in the Application object, an enumeration
Getinitparameter	Returns the initial parameter value of the specified name in the Application object
Getservletinfo	Returns the current version information in the servlet compiler
SetAttribute	Sets the property value of the specified name in the Application object

7.config Objects (configuration information for the servlet javax.servlet.ServletConfig)

Method name	Description
Getservletcontext	Returns the Environment object for the servlet being executed
Getservletname	Returns the name of the servlet being executed
Getinitparameter	Returns the initial parameter value of the specified name
Getinitparameternames	Returns all the initial parameter names in the JSP, an enumeration

8.page object (instance of current JSP, java.lang.object)

It represents a JSP that is compiled into a servlet that can be used to invoke the method defined in the Servlet class

9.exception Object (Run-time exception, java.lang.Throwable)

The result of the called Error page is only available in the error page.

That is, set in the page directive: <% @page iserrorpage= "true"%>

Request (Javax.servlet.ServletRequest) It contains information about browser requests. This object enables you to get the header information, cookies, and request parameters from the request.

Response (Javax.servlet.ServletResponse) The response returned to the user as a result of JSP page processing is stored in the object. and provides methods for setting response content, response headers, and redirects (e.g. cookies, headers, etc.)

Out (Javax.servlet.jsp.JspWriter) is used to write content to the output stream of a JSP page instance, providing several methods that you can use to echo the output to the browser.

PageContext (Javax.servlet.jsp.PageContext) describes the current JSP page's operating environment. You can return access to other implicit objects and their properties on a JSP page, and it also implements the method of transferring control from the current page to another page.

The Session object stores information about this session, or it can assign properties to a session, each with a name and a value of javax.servlet.http.HttpSession. Session objects are used primarily to store and retrieve property values.

Application (Javax.servle.ServletContext) stores contextual information about the servlet that runs the JSP page and any Web components that are in the same application.

Page (Java.lang.Object) represents the servlet instance of the current JSP page

Config (Javax.servlet.ServletConfig) This object is used to access the initialization parameters of the servlet instance.

Exception (Javax.lang.Throwable) when a page throws an exception, it is forwarded to the JSP error page, which is provided to handle the error in the JSP. The <% @page iserrorpage= "True" can only be used in the error page%>

JSP built-in Objects	function	Main Methods
Out	Output data to the client	Print () println () flush () Clear () Isautoflush () GetBufferSize () Close () ...
Request	Requesting data from the client	Getattributenames () getcookies () getparameter () getparametervalues () setattribute () ()-Getservletpath () ...
Response	Encapsulates the response generated by the JSP and is sent to the client to respond to the customer's request	Addcookie () Sendredirect () setContentType () Flushbuffer () getbuffersize () Getoutputstream () Senderror () Containsheader () ........
Application
Config	Represents the configuration of the servlet, and when a servlet initializes, the container passes some information through this object to the servlet	Getservletcontext () Getservletname () () Getinitparameter () Getinitparameternames () .....
Page	An instance of the JSP implementation class, which is the JSP itself, through which it can be accessed	Flush () .....
PageContext	Wraps the context of the page for JSP pages. Managing the question of a named object that belongs to a particular visible part of a JSP	Forward () getattribute () getexception () getrequest () GetResponse () Getservletconfig () GetSession () Getservletcontext () setattribute () RemoveAttribute () Findattribute () ........
Session	Used to hold information for each user to track the operational status of each user	GetAttribute () getId () Getattributenames () Getcreatetime () Getmaxinactiveinterval () Invalidate () IsNew ()
exception	reflect the running exception	GetMessage () ......