Class LoopTagSupport

  • All Implemented Interfaces:, LoopTag, IterationTag, JspTag, Tag, TryCatchFinally
    Direct Known Subclasses:
    ForEachSupport, ForTokensSupport

    public abstract class LoopTagSupport
    extends TagSupport
    implements LoopTag, IterationTag, TryCatchFinally

    Base support class to facilitate implementation of iteration tags.

    Since most iteration tags will behave identically with respect to actual iterative behavior, JSTL provides this base support class to facilitate implementation. Many iteration tags will extend this and merely implement the hasNext() and next() methods to provide contents for the handler to iterate over.

    In particular, this base class provides support for:

    • Iteration control, based on protected prepare(), next(), and hasNext() methods
    • Subsetting (begin, end, step>functionality, including validation of subset parameters for sensibility)
    • item retrieval (getCurrent())
    • status retrieval (LoopTagStatus)
    • exposing attributes (set by var and varStatus attributes)

    In providing support for these tasks, LoopTagSupport contains certain control variables that act to modify the iteration. Accessors are provided for these control variables when the variables represent information needed or wanted at translation time (e.g., var, varStatus). For other variables, accessors cannot be provided here since subclasses may differ on their implementations of how those accessors are received. For instance, one subclass might accept a String and convert it into an object of a specific type by using an expression evaluator; others might accept objects directly. Still others might not want to expose such information to outside control.

    See Also:
    Serialized Form
    • Constructor Detail

      • LoopTagSupport

        public LoopTagSupport()
        Constructs a new LoopTagSupport. As with TagSupport, subclasses should not implement constructors with arguments, and no-arguments constructors implemented by subclasses must call the superclass constructor.
    • Method Detail

      • release

        public void release()
        Releases any resources this LoopTagSupport may have (or inherit).
        Specified by:
        release in interface Tag
        release in class TagSupport
        See Also:
      • doFinally

        public void doFinally()
        Removes any attributes that this LoopTagSupport set.

        These attributes are intended to support scripting variables with NESTED scope, so we don't want to pollute attribute space by leaving them lying around.

        Specified by:
        doFinally in interface TryCatchFinally
      • doCatch

        public void doCatch​(java.lang.Throwable t)
                     throws java.lang.Throwable
        Rethrows the given Throwable.
        Specified by:
        doCatch in interface TryCatchFinally
        t - The throwable exception navigating through this tag.
        java.lang.Throwable - if the exception is to be rethrown further up the nest chain.
      • getCurrent

        public java.lang.Object getCurrent()
        Description copied from interface: LoopTag
        Retrieves the current item in the iteration. Behaves idempotently; calling getCurrent() repeatedly should return the same Object until the iteration is advanced. (Specifically, calling getCurrent() does not advance the iteration.)
        Specified by:
        getCurrent in interface LoopTag
        the current item as an object
      • getLoopStatus

        public LoopTagStatus getLoopStatus()
        Description copied from interface: LoopTag
        Retrieves a 'status' object to provide information about the current round of the iteration.
        Specified by:
        getLoopStatus in interface LoopTag
        The LoopTagStatus for the current LoopTag.
      • setVar

        public void setVar​(java.lang.String id)
        Sets the 'var' attribute.
        id - Name of the exported scoped variable storing the current item of the iteration.
      • setVarStatus

        public void setVarStatus​(java.lang.String statusId)
        Sets the 'varStatus' attribute.
        statusId - Name of the exported scoped variable storing the status of the iteration.