Jstl and its core (CORE) label Library

Custom JSP labels are an effective way to replace Java program fragments in JSP. Most Web application JSP files often implement some common functions. To improve the development efficiency of Web applications, Sun has developed a set of standard tag library specifications, which are calledJstl(JSP standard tag library ).

The jstl tag library actually contains five different tag libraries.Jstl1.1 SpecificationConventions are made for the Uris and prefixes of these tag libraries.

Type of jstl tag Library

Tag library name	Prefix	Uri	Description
Core	C	Http://java.sun.com/jsp/jstl/core	Core tag library, including general-purpose tags, condition tags, iteration tags, and URL-related tags
I18n	FMT	Http://java.sun.com/jsp/jstl/fmt	Includes tags for writing international web applications and tags for formatting date, time, and number
SQL	SQL	Http://java.sun.com/jsp/jstl/ SQL	Includes tags for accessing the relational database
XML	X	Http://java.sun.com/jsp/jstl/xml	Tags that contain operations on XML documents
Functions	FN	Http://java.sun.com/jsp/jstl/functions	Contains a set of general El functions that can be used in El expressions.

Using jstl requires two jar packages:

Jstl. Jar: Class file that contains interfaces and classes defined in the jstl specification.

Standard. Jar: Contains the class file that Apache open source software organization is used to implement jstl, and under its META-INF directory, contains the TLD file of the five tag libraries listed in the table above. The TLD file of each tag library describes all tags in the library, including the Tag Name and implementation class of the tag.

Jstl core tag Library:

The core tag library is the most commonly used tag library when writing JSP files. It includes the followingTag:

Tag	Description
<C: Out>	Used to print the result of an expression to a webpage.
<C: Set>	Used to set the value of a named variable. If the name variable is JavaBean, you can also set the value of the JavaBean attribute. If the name variable is map type, you can also set the value corresponding to the key in it.
<C: Remove>	Used to delete a named variable
<C: Catch>	Used to capture exceptions and place the exception object in the specified name variable
<C: If>	Used to implement the if statement function in Java
<C: Choose> <C: When> <C: otherwise>	Used to implement the IF-else statement function in Java
<C: foreach>	Used to traverse objects in the set and to repeatedly execute the label subject
<C: fortokens>	It is used to traverse the sub-strings separated by specific delimiters in a string, and the tag subject can be repeatedly executed.
<C: Import>	Used to include other web resources, similar to the <JSP: Include> command
<C: URL>	Used to reconstruct a URL based on a specific rewrite rule
<C: Redirect>	Used for redirection