javax.servlet.jsp.jstl.core
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:
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 | |
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protected int | begin Starting index ('begin' attribute) |
protected boolean | beginSpecified Boolean flag indicating whether 'begin' was specified. |
protected int | end
Ending index of the iteration ('end' attribute).
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protected boolean | endSpecified Boolean flag indicating whether 'end' was specified. |
protected String | itemId Attribute-exposing control |
protected String | statusId Attribute-exposing control |
protected int | step Iteration step ('step' attribute) |
protected boolean | stepSpecified Boolean flag indicating whether 'step' was specified. |
Constructor Summary | |
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LoopTagSupport()
Constructs a new LoopTagSupport. |
Method Summary | |
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int | doAfterBody()
Continues the iteration when appropriate -- that is, if we (a) have
more items and (b) don't run over our 'end' (given our 'step'). |
void | doCatch(Throwable t)
Rethrows the given Throwable. |
void | doFinally()
Removes any attributes that this LoopTagSupport set.
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int | doStartTag()
Begins iterating by processing the first item. |
Object | getCurrent() |
LoopTagStatus | getLoopStatus() |
protected abstract boolean | hasNext() Returns information concerning the availability of more items over which to iterate. |
protected abstract Object | next() Returns the next object over which the tag should iterate. |
protected abstract void | prepare() Prepares for a single tag invocation. |
void | release()
Releases any resources this LoopTagSupport may have (or inherit). |
void | setVar(String id)
Sets the 'var' attribute.
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void | setVarStatus(String statusId)
Sets the 'varStatus' attribute.
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protected void | validateBegin()
Ensures the "begin" property is sensible, throwing an exception
expected to propagate up if it isn't |
protected void | validateEnd()
Ensures the "end" property is sensible, throwing an exception
expected to propagate up if it isn't |
protected void | validateStep()
Ensures the "step" property is sensible, throwing an exception
expected to propagate up if it isn't |
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.
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.
Returns: true if there is at least one more item to iterate over, false otherwise
Throws: javax.servlet.jsp.JspTagException
See Also: LoopTagSupport
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.)
Returns: the java.lang.Object to use in the next round of iteration
Throws: java.util.NoSuchElementException if next() is called but no new elements are available javax.servlet.jsp.JspTagException for other, unexpected exceptions
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.
Throws: javax.servlet.jsp.JspTagException
Parameters: id Name of the exported scoped variable storing the current item of the iteration.
Parameters: statusId Name of the exported scoped variable storing the status of the iteration.