logic


Standard Syntax:
     <%@ taglib prefix="logic" uri="http://struts.apache.org/tags-logic" %>

XML Syntax:
     <anyxmlelement xmlns:logic="http://struts.apache.org/tags-logic" />

Note: Some of the features in this taglib are also available in the JavaServer Pages Standard Tag Library (JSTL). The Struts team encourages the use of the standard tags over the Struts specific tags when possible.

This tag library contains tags that are useful in managing conditional generation of output text, looping over object collections for repetitive generation of output text, and application flow management.

For tags that do value comparisons (equal, greaterEqual, greaterThan, lessEqual, lessThan, notEqual), the following rules apply:

For tags that do substring matching (match, notMatch), the following rules apply:

Many of the tags in this tag library will throw a JspException at runtime when they are utilized incorrectly (such as when you specify an invalid combination of tag attributes). JSP allows you to declare an "error page" in the <%@ page %> directive. If you wish to process the actual exception that caused the problem, it is passed to the error page as a request attribute under key org.apache.struts.action.EXCEPTION.

Tag Library Information
Display NameNone
Version1.3
Short Namelogic
URIhttp://struts.apache.org/tags-logic
 

Tag Summary
empty

Evaluate the nested body content of this tag if the requested variable is either null or an empty string.

This tag evaluates its nested body content only if the specified value is either absent (i.e. null), an empty string (i.e. a java.lang.String with a length of zero), or an empty java.util.Collection or java.util.Map (tested by the .isEmpty() method on the respective interface).

JSTL: The equivalent JSTL tag is <c:if> using the empty operator. For example,
<c:if test="${empty sessionScope.myBean.myProperty}"> do something </c:if>

Since:
Struts 1.1
equal

Evaluate the nested body content of this tag if the requested variable is equal to the specified value.

Compares the variable specified by one of the selector attributes against the specified constant value. The nested body content of this tag is evaluated if the variable and value are equal.

greaterEqual

Evaluate the nested body content of this tag if the requested variable is greater than or equal to the specified value.

Compares the variable specified by one of the selector attributes against the specified constant value. The nested body content of this tag is evaluated if the variable is greater than or equal to the value.

greaterThan

Evaluate the nested body content of this tag if the requested variable is greater than the specified value.

Compares the variable specified by one of the selector attributes against the specified constant value. The nested body content of this tag is evaluated if the variable is greater than the value.

iterate

Repeat the nested body content of this tag over a specified collection.

Repeats the nested body content of this tag once for every element of the specified collection, which must be a Collection. The collection to be iterated over must be specified in one of the following ways:

  • As a runtime expression specified as the value of the collection attribute.
  • As a SourceBean collection specified by the name attribute.

If the collection you are iterating over can contain null values, the loop will still be performed but no page scope attribute (named by the id attribute) will be created for that loop iteration. You can use the <logic:present> and <logic:notPresent> tags to test for this case.

lessEqual

Evaluate the nested body content of this tag if the requested variable is less than or equal to the specified value.

Compares the variable specified by one of the selector attributes against the specified constant value. The nested body content of this tag is evaluated if the variable is less than or equal to the value.

lessThan

Evaluate the nested body content of this tag if the requested variable is less than the specified value.

Compares the variable specified by one of the selector attributes against the specified constant value. The nested body content of this tag is evaluated if the variable is less than the value.

match

Evaluate the nested body content of this tag if the specified value is an appropriate substring of the requested variable.

Matches the variable specified by one of the selector attributes (as a String) against the specified constant value. If the value is a substring (appropriately limited by the location attribute), the nested body content of this tag is evaluated.

notEmpty

Evaluate the nested body content of this tag if the requested variable is neither null, nor an empty string, nor an empty java.util.Collection (tested by the .isEmpty() method on the java.util.Collection interface).

This tag evaluates its nested body content only if the specified value is present (i.e. not null) and is not an empty string (i.e. a java.lang.String with a length of zero).

JSTL: The equivalent JSTL tag is <c:if> using the ! empty operator. For example,
<c:if test="${ ! empty sessionScope.myBean.myProperty}"> do something </c:if>

notEqual

Evaluate the nested body content of this tag if the requested variable is not equal to the specified value.

Compares the variable specified by one of the selector attributes against the specified constant value. The nested body content of this tag is evaluated if the variable and value are not equal.

notMatch

Evaluate the nested body content of this tag if the specified value is not an appropriate substring of the requested variable.

Matches the variable specified by one of the selector attributes (as a String) against the specified constant value. If the value is not a substring (appropriately limited by the location attribute), the nested body content of this tag is evaluated.

notPresent

Generate the nested body content of this tag if the specified value is not present in this request.

Depending on which attribute is specified, this tag checks the current request, and evaluates the nested body content of this tag only if the specified value is not present. Only one of the attributes may be used in one occurrence of this tag.

present

Generate the nested body content of this tag if the specified value is present in this request.

Depending on which attribute is specified, this tag checks the current request, and evaluates the nested body content of this tag only if the specified value is present. Only one of the attributes may be used in one occurrence of this tag.

redirect

Render an HTTP Redirect

Performs an HttpServletResponse.sendRedirect() call to the hyperlink specified by the attributes to this tag. URL rewriting will be applied automatically, to maintain session state in the absence of cookies.

The base URL for this redirect is calculated based on the href

Normally, the redirect you specify will be left unchanged (other than URL rewriting if necessary). However, there are two ways you can append one or more dynamically defined query parameters to the hyperlink -- specify a single parameter with the paramId attribute (and its associated attributes to select the value), or specify the name attribute to select a SourceBean list that contains one or more parameter ids and corresponding values.

To specify a single parameter, use the paramId attribute to define the name of the request parameter to be submitted. To specify the corresponding value, specify the paramName attribute - The named property on service context (optionally scoped by the value of the paramScope attribute) must identify a value that can be converted to a String.

If you prefer to specify a SourceBean list that contains all of the request parameters to be added to the hyperlink, specify only the name attribute - The named service context data (optionally scoped by the value of the scope attribute) must identify a SourceBean list containing the parameters.

As the SourceBean list is processed, every element is assumed to be formed by the name and value attributes; these respective values are used as query parameters to be appended to the hyperlink. The value associated with each SourceBean must be either a String or an object whose toString() method will be called.

Additionally, you can request that the current transaction control token, if any, be included in the generated hyperlink by setting the transaction attribute to true. You can also request that the href is calculated based on the alias and aliasRelated parameters.

 


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