JSP Day 2

<JSP: usebean id = "today" class = "Java. util. Date" Scope = "request"> </jsp: usebean>
==>
Object o = request. getattribute ("today ");
If (o! = NULL ){
Date today = (date) O;
} Else {
Date today = new java. util. Date ();
Request. setattribute ("today", today );
}
The class is first searched. If it cannot be found, a new object is created and the attribute is set in the range.

<JSP: usebean id = "today" type = "Java. util. Date" Scope = "request"> </jsp: usebean>
==>
Object o = request. getattribute ("today ");
If (o! = NULL ){
Date today = (date) O;
} Else {
Throw new exception ("unable to find the information named today in scope ");
}
Type is searched first. If no value is found, an exception is reported.
Applicable to multi-state environments

<JSP: setproperty property = "Birthday" name = "p" value = "<% = request. getparameter (" Birthday ") %>"/>
==>
String Birthday = request. getparameter ("Birthday ");
P. setbirthday (birthday );

<JSP: setproperty property = "name" name = "p"/>
==>
String name = request. getparamter ("name ");
P. setname (name );
If no value is set, the system queries parameters with the same name from the page by default. Set the value

<JSP: setproperty property = "*" name = "p"/>
="
Get all attribute names in object P
Use each attribute name as a parameter name to find the parameter values on the page.
Set Object Property Values

========================================================== ========
Prerequisites:
Control name = property name in the object class on the page
========================================================== ========

<JSP: getproperty property = "name" name = "p"/>
="
P. getname ();

The role of the page:
1. Accept user input data
<Form...>
2. Obtain the data stored in a certain range and present the data to the client.
<JSP: usebean id = "" type = "" Scope = ">

Jump path:
We recommend that you use absolute path, that is, starting /.
In HTML and redirect redirection,/Application name/request...
In forward jump,/request...

Java code left in JSP:
1. Code for getting data
Parameters
Attribute
System internal information
2. Logical branches and cyclic statements

El: Expression Language
Syntax structure:
$ {...}
Purpose:
Obtain and display data
Data includes:
* Parameters
$ {Param. parameter name}
="
Request. getparameter ("parameter name ");

$ {Paramvalues. parameter name}
Obtain multiple parameter values with the same name
Request. getparametervalues ("parameter name ")
* Attributes
$ {Attribute name}
="
Pagecontext. findattribute ("attribute name ");

Pagecontext ----- indicates the current Web Application
Getattribute ("attribute name", range)
Pagecontext. request_scope
Pagecontext. session_scope
Pagecontext. application_scope
Setattribute ("attribute name", "attribute value", Set range)
Pagecontext. request_scope
Pagecontext. session_scope
Pagecontext. application_scope
Findattribute ("attribute name ")
Request ==> session ==> search for properties in the application in sequence, locate and stop. If no value is found, null is returned.

$ {Built-in object name. attribute name}
==>
Pagecontext. getattribute ("attribute name", built-in object name)
* Internal system information
$ {Pagecontext. Object Name ....}
El common built-in objects
Requestscope
Sessionscope
Applicationscope

Supported data in El:
 
<Integer_literal>
<Floating_point_literal>
<String_literal>
"True", "false"
"Null"
"("
"-"
"Not"
"! "
"Empty"
<Identifier>
 
Operators supported in El:
"}",". ","> "," GT "," <"," LT "," = "," EQ "," <= "," Le ", "> =", "Ge ","! = "," Ne "," ["," + ","-"," * ","/"," Div "," % "," Mod ", "and", "&", "or", "| ","? "

 
Pagecontext. getrequest (): servletrequest
Request. getcontextpath ();
==>
$ {Pagecontext. Request. contextpath}