Jsp jstl label language library and jspjstl label
The el language $ {} is used by default in jsp. I didn't expect jstl labels to be unavailable in jsp. You need to import jstl. jar and standard. jar to identify and use them.
If jsp is used in development, the tag language must be used, because apart from static html content, other data obtained from the background database usually needs to be converted and judged.
There is a c. tld file in standard. jar;
This should be <% @ taglib prefix = "c" uri = "https://java.sun.com/jsp/jstl/core" %>, which is the tag definition in the core tag library.
After the core tag is introduced, the following available labels are available:
Label description
Used to display data in JSP, just like <% =...>
Used to save data
Used to delete data
Used to handle exceptions that generate errors and store error information
Same as if in general programs
Only
And
Parent tag
To determine whether a condition is true.
Sub-tag, connected
After the tag, when
Executed when the tag is determined to be false.
Retrieve an absolute or relative URL and expose its content to the page
Basic iteration tag, accepting multiple Collection types
Separate the content based on the specified separator and iterate the output
Used to pass parameters to pages that contain or redirect
Redirects to a new URL.
Use optional query parameters to create a URL
I don't know if there will be any overlap with the Tag feature provided by jsp, but I usually like to use jstl.
Let's take a look at the most common if label definition:
Simple conditional tag, which evalutes its body if the supplied condition is true and optionally exposes a Boolean scripting variable representing the evaluation of this condition
if
org.apache.taglibs.standard.tag.rt.core.IfTag
JSP
test
true
true
boolean
var
false
false
scope
false
false
The top to bottom means:
Description: description, which is not translated in English.
Name: the name of the tag. You can use
Attribute: attributes that can be used by tags, including test \ var \ scope.
Test is the condition for judgment,
Var is the result after judgment. It is true or false. The value of var is used to store the result, and then the result can be obtained through this value.
For example, if var = "test", you can get the test result from $ {name }.
Scope. jsp has four scopes: request, session, and put one: scope = "request"
False is not required.
The content between the start and end tags of if is determined based on the true and false values of test.
Next:
Out tag Definition
Like <%= ... >, but for expressions.
out
org.apache.taglibs.standard.tag.rt.core.OutTag
JSP
value
true
true
default
false
true
escapeXml
false
true
Value is required. Generally, its value is an el expression, otherwise it is static content.
Default value. If the value cannot be obtained, the default value is displayed,
EscapeXml specifies whether the content is displayed in plain text. The default value is true. If this attribute is available, HTML text is displayed.
The content between the out labels is not displayed.
All right, all content is finished!