javax.servlet.jsp.jstl.core

Class LoopTagSupport

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.

Author: Shawn Bayern

Field Summary
protected intbegin
Starting index ('begin' attribute)
protected booleanbeginSpecified
Boolean flag indicating whether 'begin' was specified.
protected intend
Ending index of the iteration ('end' attribute).
protected booleanendSpecified
Boolean flag indicating whether 'end' was specified.
protected StringitemId
Attribute-exposing control
protected StringstatusId
Attribute-exposing control
protected intstep
Iteration step ('step' attribute)
protected booleanstepSpecified
Boolean flag indicating whether 'step' was specified.
Constructor Summary
LoopTagSupport()
Constructs a new LoopTagSupport.
Method Summary
intdoAfterBody()
Continues the iteration when appropriate -- that is, if we (a) have more items and (b) don't run over our 'end' (given our 'step').
voiddoCatch(Throwable t)
Rethrows the given Throwable.
voiddoFinally()
Removes any attributes that this LoopTagSupport set.
intdoStartTag()
Begins iterating by processing the first item.
ObjectgetCurrent()
LoopTagStatusgetLoopStatus()
protected abstract booleanhasNext()

Returns information concerning the availability of more items over which to iterate.

protected abstract Objectnext()

Returns the next object over which the tag should iterate.

protected abstract voidprepare()

Prepares for a single tag invocation.

voidrelease()
Releases any resources this LoopTagSupport may have (or inherit).
voidsetVar(String id)
Sets the 'var' attribute.
voidsetVarStatus(String statusId)
Sets the 'varStatus' attribute.
protected voidvalidateBegin()
Ensures the "begin" property is sensible, throwing an exception expected to propagate up if it isn't
protected voidvalidateEnd()
Ensures the "end" property is sensible, throwing an exception expected to propagate up if it isn't
protected voidvalidateStep()
Ensures the "step" property is sensible, throwing an exception expected to propagate up if it isn't

Field Detail

begin

protected int begin
Starting index ('begin' attribute)

beginSpecified

protected boolean beginSpecified
Boolean flag indicating whether 'begin' was specified.

end

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.

endSpecified

protected boolean endSpecified
Boolean flag indicating whether 'end' was specified.

itemId

protected String itemId
Attribute-exposing control

statusId

protected String statusId
Attribute-exposing control

step

protected int step
Iteration step ('step' attribute)

stepSpecified

protected boolean stepSpecified
Boolean flag indicating whether 'step' was specified.

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

doAfterBody

public 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').

doCatch

public void doCatch(Throwable t)
Rethrows the given Throwable.

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.

doStartTag

public int doStartTag()
Begins iterating by processing the first item.

getCurrent

public Object getCurrent()

getLoopStatus

public LoopTagStatus getLoopStatus()

hasNext

protected abstract boolean hasNext()

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

next

protected abstract Object next()

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

prepare

protected abstract void prepare()

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

release

public void release()
Releases any resources this LoopTagSupport may have (or inherit).

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.

validateBegin

protected void validateBegin()
Ensures the "begin" property is sensible, throwing an exception expected to propagate up if it isn't

validateEnd

protected void validateEnd()
Ensures the "end" property is sensible, throwing an exception expected to propagate up if it isn't

validateStep

protected void validateStep()
Ensures the "step" property is sensible, throwing an exception expected to propagate up if it isn't
Copyright 2003 Sun Microsystems, Inc. All Rights Reserved.