org.apache.velocity.tools.generic
Class IteratorTool

java.lang.Object
  org.apache.velocity.tools.generic.IteratorTool

All Implemented Interfaces:

java.util.Iterator

public class IteratorTool
extends java.lang.Object
implements java.util.Iterator

A convenience tool to use with #foreach loops. It wraps a list to let the designer specify a condition to terminate the loop, and reuse the same list in different loops.

Example of use:

  Java
  ----
  context.put("mill", new IteratorTool());


  VTL
  ---

  #set ($list = [1, 2, 3, 5, 8, 13])
  #set ($numbers = $mill.wrap($list))

  #foreach ($item in $numbers)
  #if ($item < 8) $numbers.more()#end
  #end

  $numbers.more()


  Output
  ------

   1 2 3 5
  8

 Example toolbox.xml config (if you want to use this with VelocityView):
 <tool>
   <key>mill</key>
   <scope>request</scope>
   <class>org.apache.velocity.tools.generic.IteratorTool</class>
 </tool>
 

Warning: It is not recommended to use hasNext() with this tool as it is used to control the #foreach. Use hasMore() instead.

Version:

$Id: IteratorTool.java 477914 2006-11-21 21:52:11Z henning $

Author:

Denis Bredelet

Field Summary

private boolean	cachedNext
private java.util.Iterator	iterator
protected java.lang.Object	next
private boolean	wantMore
private java.lang.Object	wrapped

Constructor Summary

IteratorTool()
Create a IteratorTool instance to use as tool.

IteratorTool(java.lang.Object wrapped)
Create a IteratorTool instance to use in #foreach.

Method Summary

boolean	hasMore() Returns true if there are more elements in the wrapped list.
boolean	hasNext() Returns true if there are more elements in the list and more() was called.
private void	internalWrap(java.lang.Object wrapped) Wraps a list with the tool.
java.lang.Object	more() Asks for the next element in the list.
java.lang.Object	next() Gets the next object in the list.
void	remove() Removes the current element from the list.
void	reset() Resets the wrapper so that it starts over at the beginning of the list.
void	stop() Puts a condition to break out of the loop.
java.lang.String	toString() Returns this object as a String.
IteratorTool	wrap(java.lang.Object list) Wraps a list with the tool.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

wrapped

private java.lang.Object wrapped

iterator

private java.util.Iterator iterator

wantMore

private boolean wantMore

cachedNext

private boolean cachedNext

next

protected java.lang.Object next

Constructor Detail

IteratorTool

public IteratorTool()

Create a IteratorTool instance to use as tool. When it is created this way, the tool returns a new instance each time wrap() is called. This is useful when you want to allow the designers to create instances.

IteratorTool

public IteratorTool(java.lang.Object wrapped)

Create a IteratorTool instance to use in #foreach.

Parameters:

wrapped - The list to wrap.

Method Detail

wrap

public IteratorTool wrap(java.lang.Object list)

Wraps a list with the tool.
The list can be an array, a Collection, a Map, an Iterator or an Enumeration.
If the list is a Map, the tool iterates over the values.
If the list is an Iterator or an Enumeration, the tool can be used only once.

Parameters:

list - The list to wrap.

Returns:

A new wrapper if this object is used as a tool, or itself if it is a wrapper.

internalWrap

private void internalWrap(java.lang.Object wrapped)

Wraps a list with the tool. This object can therefore be used instead of the list itself in a #foreach. The list can be an array, a Collection, a Map, an Iterator or an Enumeration.
- If the list is a Map, the tool iterates over the values.
- If the list is an Iterator or an Enumeration, the tool can be used only once.

Parameters:

wrapped - The list to wrap.

reset

public void reset()

Resets the wrapper so that it starts over at the beginning of the list.

Note to programmers: This method has no effect if the wrapped object is an enumeration or an iterator.

next

public java.lang.Object next()

Gets the next object in the list. This method is called by #foreach to define $item in:

 #foreach( $item in $list )
 

This method is not intended for template designers, but they can use them if they want to read the value of the next item without doing more().

Specified by:

next in interface java.util.Iterator

Returns:

The next item in the list.

Throws:

NoSuchElementException - if there are no more elements in the list.

hasNext

public boolean hasNext()

Returns true if there are more elements in the list and more() was called.
This code always return false:

 tool.hasNext()? tool.hasNext(): false;
 

Specified by:

hasNext in interface java.util.Iterator

Returns:

true if there are more elements, and either more() or hasNext() was called since last call.

remove

public void remove()
            throws java.lang.UnsupportedOperationException

Removes the current element from the list. The current element is defined as the last element that was read from the list, either with next() or with more().

Specified by:

remove in interface java.util.Iterator

Throws:

java.lang.UnsupportedOperationException - if the wrapped list iterator doesn't support this operation.

more

public java.lang.Object more()

Asks for the next element in the list. This method is to be used by the template designer in #foreach loops.

If this method is called in the body of #foreach, the loop continues as long as there are elements in the list.
If this method is not called the loop terminates after the current iteration.

Returns:

The next element in the list, or null if there are no more elements.

hasMore

public boolean hasMore()

Returns true if there are more elements in the wrapped list.
If this object doesn't wrap a list, the method always returns false.

Returns:

true if there are more elements in the list.

stop

public void stop()

Puts a condition to break out of the loop. The #foreach loop will terminate after this iteration, unless more() is called after stop().

toString

public java.lang.String toString()

Returns this object as a String.
If this object is used as a tool, it just gives the class name.
Otherwise it appends the wrapped list to the class name.

Overrides:

toString in class java.lang.Object

Returns:

A string representation of this object.