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javax.servlet.jsp.jstl.core
abstract public class: LoopTagSupport [javadoc | source]
java.lang.Object
   javax.servlet.jsp.tagext.TagSupport
      javax.servlet.jsp.jstl.core.LoopTagSupport

All Implemented Interfaces:
    LoopTag, TryCatchFinally, IterationTag, Serializable

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:

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.

Field Summary
protected  int begin    Starting index ('begin' attribute) 
protected  int end    Ending index of the iteration ('end' attribute). A value of -1 internally indicates 'no end specified', although accessors for the core JSTL tags do not allow this value to be supplied directly by the user. 
protected  int step    Iteration step ('step' attribute) 
protected  boolean beginSpecified    Boolean flag indicating whether 'begin' was specified. 
protected  boolean endSpecified    Boolean flag indicating whether 'end' was specified. 
protected  boolean stepSpecified    Boolean flag indicating whether 'step' was specified. 
protected  String itemId    Attribute-exposing control 
protected  String statusId     
protected  ValueExpression deferredExpression    The deferred expression if any 
Fields inherited from javax.servlet.jsp.tagext.TagSupport:
id,  pageContext
Constructor:
 public LoopTagSupport() 
Method from javax.servlet.jsp.jstl.core.LoopTagSupport Summary:
doAfterBody,   doCatch,   doFinally,   doStartTag,   getCurrent,   getDelims,   getLoopStatus,   hasNext,   next,   prepare,   release,   setVar,   setVarStatus,   validateBegin,   validateEnd,   validateStep
Methods from javax.servlet.jsp.tagext.TagSupport:
doAfterBody,   doEndTag,   doStartTag,   findAncestorWithClass,   getId,   getParent,   getValue,   getValues,   release,   removeValue,   setId,   setPageContext,   setParent,   setValue
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from javax.servlet.jsp.jstl.core.LoopTagSupport Detail:
 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').
 public  void doCatch(Throwable t) throws Throwable 
    Rethrows the given Throwable.
 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.

 public int doStartTag() throws JspException 
    Begins iterating by processing the first item.
 public Object getCurrent() 
 protected String getDelims() 
 public LoopTagStatus getLoopStatus() 
 abstract protected boolean hasNext() throws JspTagException

    Returns information concerning the availability of more items over which to iterate. This method must be provided by concrete subclasses of LoopTagSupport to assist the iterative logic provided by the supporting base class.

    See next for more information about the purpose and expectations behind this tag.

 abstract protected Object next() throws JspTagException

    Returns the next object over which the tag should iterate. This method must be provided by concrete subclasses of LoopTagSupport to inform the base logic about what objects it should iterate over.

    It is expected that this method will generally be backed by an Iterator, but this will not always be the case. In particular, if retrieving the next object raises the possibility of an exception being thrown, this method allows that exception to propagate back to the JSP container as a JspTagException; a standalone Iterator would not be able to do this. (This explains why LoopTagSupport does not simply call for an Iterator from its subtags.)

 abstract protected  void prepare() throws JspTagException

    Prepares for a single tag invocation. Specifically, allows subclasses to prepare for calls to hasNext() and next(). Subclasses can assume that prepare() will be called once for each invocation of doStartTag() in the superclass.

 public  void release() 
    Releases any resources this LoopTagSupport may have (or inherit).
 public  void setVar(String id) 
    Sets the 'var' attribute.
 public  void setVarStatus(String statusId) 
    Sets the 'varStatus' attribute.
 protected  void validateBegin() throws JspTagException 
    Ensures the "begin" property is sensible, throwing an exception expected to propagate up if it isn't
 protected  void validateEnd() throws JspTagException 
    Ensures the "end" property is sensible, throwing an exception expected to propagate up if it isn't
 protected  void validateStep() throws JspTagException 
    Ensures the "step" property is sensible, throwing an exception expected to propagate up if it isn't