LoopTagSupport

java.lang.Object
- jakarta.servlet.jsp.tagext.TagSupport
- - jakarta.servlet.jsp.jstl.core.LoopTagSupport

All Implemented Interfaces:

LoopTag, IterationTag, JspTag, Tag, TryCatchFinally, java.io.Serializable
```
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, the Jakarta Standard Tag Library 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

Field Summary

Fields
Modifier and Type	Field and Description
`protected int`	`begin` Starting index ('begin' attribute)
`protected boolean`	`beginSpecified` Boolean flag indicating whether 'begin' was specified.
`protected ValueExpression`	`deferredExpression` The deferred expression if any
`protected int`	`end` Ending index of the iteration ('end' attribute).
`protected boolean`	`endSpecified` Boolean flag indicating whether 'end' was specified.
`protected java.lang.String`	`itemId` Attribute-exposing control
`protected java.lang.String`	`statusId` Attribute-exposing control
`protected int`	`step` Iteration step ('step' attribute)
`protected boolean`	`stepSpecified` Boolean flag indicating whether 'step' was specified.

Fields inherited from class jakarta.servlet.jsp.tagext.TagSupport
id, pageContext

Fields inherited from interface jakarta.servlet.jsp.tagext.IterationTag
EVAL_BODY_AGAIN

Fields inherited from interface jakarta.servlet.jsp.tagext.Tag
EVAL_BODY_INCLUDE, EVAL_PAGE, SKIP_BODY, SKIP_PAGE

Constructor Summary

Constructors
Constructor and Description

LoopTagSupport()
Constructs a new LoopTagSupport.

Constructors
Constructor and Description
`LoopTagSupport()` Constructs a new LoopTagSupport.

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`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(java.lang.Throwable t)` Rethrows the given Throwable.
`void`	`doFinally()` Removes any attributes that this LoopTagSupport set.
`int`	`doStartTag()` Begins iterating by processing the first item.
`java.lang.Object`	`getCurrent()` Retrieves the current item in the iteration.
`protected java.lang.String`	`getDelims()`
`LoopTagStatus`	`getLoopStatus()` Retrieves a 'status' object to provide information about the current round of the iteration.
`protected abstract boolean`	`hasNext()` Returns information concerning the availability of more items over which to iterate.
`protected abstract java.lang.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(java.lang.String id)` Sets the 'var' attribute.
`void`	`setVarStatus(java.lang.String statusId)` Sets the 'varStatus' attribute.
`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

Methods inherited from class jakarta.servlet.jsp.tagext.TagSupport
doEndTag, findAncestorWithClass, getId, getParent, getValue, getValues, removeValue, setId, setPageContext, setParent, setValue

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface jakarta.servlet.jsp.tagext.Tag
doEndTag, getParent, setPageContext, setParent

- Field Detail
  - begin
```
protected int begin
```
    Starting index ('begin' attribute)
  - 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 Jakarta Standard Tag Library tags do not allow this value to be supplied directly by the user.
  - step
```
protected int step
```
    Iteration step ('step' attribute)
  - beginSpecified
```
protected boolean beginSpecified
```
    Boolean flag indicating whether 'begin' was specified.
  - endSpecified
```
protected boolean endSpecified
```
    Boolean flag indicating whether 'end' was specified.
  - stepSpecified
```
protected boolean stepSpecified
```
    Boolean flag indicating whether 'step' was specified.
  - itemId
```
protected java.lang.String itemId
```
    Attribute-exposing control
  - statusId
```
protected java.lang.String statusId
```
    Attribute-exposing control
  - deferredExpression
```
protected ValueExpression deferredExpression
```
    The deferred expression if any
- 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
  - next
```
protected abstract java.lang.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.)
    
    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
    
    JspTagException - for other, unexpected exceptions
  - hasNext
```
protected abstract 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.
    
    Returns:
    
    true if there is at least one more item to iterate over, false otherwise
    
    Throws:
    
    JspTagException - thrown on error
    
    See Also:
    
    next()
  - prepare
```
protected abstract 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.
    
    Throws:
    
    JspTagException - thrown on error
  - 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:
    
    Tag.release()
  - 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:
    
    Tag.doStartTag()
  - 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:
    
    IterationTag.doAfterBody()
  - 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
    
    Parameters:
    
    t - The throwable exception navigating through this tag.
    
    Throws:
    
    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
    
    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.
  - getDelims
```
protected java.lang.String getDelims()
```
  - setVar
```
public void setVar(java.lang.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(java.lang.String statusId)
```
    Sets the 'varStatus' attribute.
    
    Parameters:
    
    statusId - Name of the exported scoped variable storing the status of the iteration.
  - validateBegin
```
protected void validateBegin()
                      throws JspTagException
```
    Ensures the "begin" property is sensible, throwing an exception expected to propagate up if it isn't
    
    Throws:
    
    JspTagException - thrown on error
  - validateEnd
```
protected void validateEnd()
                    throws JspTagException
```
    Ensures the "end" property is sensible, throwing an exception expected to propagate up if it isn't
    
    Throws:
    
    JspTagException - thrown on error
  - validateStep
```
protected void validateStep()
                     throws JspTagException
```
    Ensures the "step" property is sensible, throwing an exception expected to propagate up if it isn't
    
    Throws:
    
    JspTagException - thrown on error

Class LoopTagSupport

Field Summary

Fields inherited from class jakarta.servlet.jsp.tagext.TagSupport

Fields inherited from interface jakarta.servlet.jsp.tagext.IterationTag

Fields inherited from interface jakarta.servlet.jsp.tagext.Tag

Constructor Summary

Method Summary

Methods inherited from class jakarta.servlet.jsp.tagext.TagSupport

Methods inherited from class java.lang.Object

Methods inherited from interface jakarta.servlet.jsp.tagext.Tag

Field Detail

begin

end

step

beginSpecified

endSpecified

stepSpecified

itemId

statusId

deferredExpression

Constructor Detail

LoopTagSupport

Method Detail

next

hasNext

prepare

release

doStartTag

doAfterBody

doFinally

doCatch

getCurrent

getLoopStatus

getDelims

setVar

setVarStatus

validateBegin

validateEnd

validateStep