Core tag library of JSP standard tag Library

I. Core tag libraries mainly include general tags, condition tags, iteration tags, and URL-related tags.

Add the code at the beginning of the JSP file using the core tag Library:
<% @ Taglib uri = "http://java.sun.com/jsp/jstl/core" prefix = "C" %>
II. General Purpose labels, such as <C: Out>, <C: Set>, <C: Remove>, and <C: Catch>

1. The <C: Out> label is used for output.

Output the computing result to the jspwriter object.

Syntax 1: no body.

<C: Out value = "value" [escapexml = "{true | false}"] [default = "defaultvalue"]/>

Syntax 2: body.

<C: Out value = "value" [escapexml = "{true | false}"]>

Defaultvalue <! --- It can be JSP code->

</C: Out>

Attribute:

Value: object, the expression to be calculated ).

Excapexml: Boolean, determines whether the following characters are converted into character entity code in the result string. The default value is true.

Character	Character entity
<	& Lt;
>	& Gt;
&	& Amp;
' "	& #039; & #034;

Default: object. If the value is null, the default value is output.

2. The <C: Set> label is used to assign values.

This label is used to set a value in a certain range (request, session, application, etc.) or set the attributes of an object.

Syntax 1: Use the value attribute to set attributes in a specific range.

<C: Set Value = "value" Var = "varname" [scope = "{page | request | session | application}"]/>

Syntax 2: Use the value attribute to set an attribute in a specific range with a body.

<C: Set Var = "varname" [scope = "{page | request | session | application}"]>

Body content

</C: Set>

Syntax 3: Set an attribute of a specific object.

<C: Set Value = "value" target = "target" property = "propertyname"/>

Syntax 4: Set an attribute of a specific object and the tag has a body.

<C: set target = "target" property = "propertyname">

Body content

</C: Set>

Attribute:

Value: object, the expression to be calculated

VaR: String, used to indicate the attribute of the value.

Scope: Valid range of string and VaR

Target: string, the object to be set. It must be a JavaBeans or Java. util. map object.

Property: object, the name of the property in the target object to be set

3. <C: Remove> This label is used to delete a variable or attribute.

Syntax:

<C: Remove Var = "varname" [scope = "{page | request | session | application}"]/>

Attribute:

Scope: string, the range of this parameter.

VaR: string, the name of the parameter to be deleted

4. <C: Catch> capture exceptions thrown by labels nested in it.

Syntax:

<C: catch [Var = "varname"]>

Nestedactions

</C: Catch>

Attribute:

VaR: String, used to indicate the name of the exception

3. Condition tags

In jstl, condition labels are;

<C: If>

<C: Choose>

<C: When>

<C: otherwise>

The following sections describe each other.

1. <C: If> is used for condition determination. If its test attribute is true, its body is calculated.

Syntax 1: no body.

<C: If test = "testcondition" Var = "varname" [scope = {page | request | session | application}]/>

Syntax 2: bosy.

<C: If

Test = "testcondition"

[Var = "varname"]

[Scope = {page | request | session | application}]>

Body content

</C: If>

Attribute:

Test: Boolean, a condition of the expression

VaR: string, the value calculated by the test condition expression. Its type is boolean.

Scope: range of string and VaR

2,<C: Choose>Used for condition selection. It is used with <C: When> and <C: otherwise>.

Syntax:

<C: Choose>

Body content (<when> and <otherwise> subtags)

</Choose>

Note: its body content can only consist of the following elements:

Space.

0 or more <when> sub-labels, <when> must appear before <otherwise> labels.

0 or more <otherwise> sub-labels.

3,

<C: When>

It represents a condition branch of <C: Choose>.

Syntax:

<C: When test = "testcondition">

Body content

</C: When>

Attribute:

Test: Boolean, a condition of the expression

It has two restrictions:

<C: Choose> must be used as its parent label.

Must appear before <C: othewise>.

4,<C: otherwise>It represents the final choice of <C: Choose>.

Syntax:

<C: otherwise>

Conditional Block

</C: otherwise>

There are two restrictions on its use.

<C: Choose> must be used as its parent label.

It must be the last branch of <C: Choose>.

IV,Iteration tag

In jstl, iteration labels include:

<C: foreach>

<C: fortokens>

1. <C: foreach>

-A tag is used to iterate over a set containing multiple objects, repeat its TAG body, or repeat a fixed number of iterations.

Iterates the bodycontent of an object in a collection, or repeats the iteration for a fixed number of times.

Syntax 1: iteration in collection.

<C: foreach

[Var = "varname"]

Items = "collection"

[Varstatus = "varstatusname"]

[Begin = "begin"]

[END = "end"] [step = "step"]>

Body content

</C: foreach>

Syntax 2: Fixed iterations.

<C: foreach

[Var = "varname"]

[Varstatus = "varstatusname"]

Begin = "begin"

End = "end"

[Step = "step"]>

Body content

</C: foreach>

Attribute:

VaR: string, the name of the iteration parameter.

Items: the set of items to be iterated for any supported types.

Varstatus: String, indicating the iteration status. You can access the iteration information.

Begin: Int. If items is specified, iteration starts from index [begin] of items. If items is not specified, iteration starts from the specified index, it is equivalent to the for (INT I = begin;) statement.

End: Int. If items is specified, the iteration ends at the index [end] of items. If items is not specified, the iteration ends at the specified index, which is equivalent to (; I <end ;).

Step: int, the iteration step.

2. <C: fortokens> label

-<C: fortokens> A tag is used to browse all members of a string. Its members are separated by delimiters.

<C: fortokensitems = "A: B: C: D" delims = ":" Var = "token">

<C: Out value = "$ {token}"/> <br>

</C: fortokens>