Package javax.servlet.jsp.jstl.core

Class LoopTagSupport

java.lang.Object
javax.servlet.jsp.tagext.TagSupport
javax.servlet.jsp.jstl.core.LoopTagSupport
All Implemented Interfaces:
Serializable, 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:

  • Constructor Details

    • 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 Details

    • release

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

    • doStartTag

      public int doStartTag() throws JspException
      Begins iterating by processing the first item.
      Specified by:
      doStartTag in interface Tag
      Overrides:
      doStartTag in class TagSupport
      Returns:
      SKIP_BODY
      Throws:
      JspException - if an error occurs while processing this tag
      See Also:

    • doAfterBody

      public int doAfterBody() throws JspException
      Continues the iteration when appropriate -- that is, if we (a) have more items and (b) don't run over our 'end' (given our 'step').
      Specified by:
      doAfterBody in interface IterationTag
      Overrides:
      doAfterBody in class TagSupport
      Returns:
      SKIP_BODY
      Throws:
      JspException - if an error occurs while processing this tag
      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(Throwable t) throws Throwable
      Rethrows the given Throwable.
      Specified by:
      doCatch in interface TryCatchFinally
      Parameters:
      t - The throwable exception navigating through this tag.
      Throws:
      Throwable - if the exception is to be rethrown further up the nest chain.

    • getCurrent

      public 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
      Returns:
      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
      Returns:
      The LoopTagStatus for the current LoopTag.

    • setVar

      public void setVar(String id)
      Sets the 'var' attribute.
      Parameters:
      id - Name of the exported scoped variable storing the current item of the iteration.

    • setVarStatus

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