sirius.kernel.commons

Class Limit

java.lang.Object

sirius.kernel.commons.Limit

public class Limit
extends Object

Helper class to handle result windowing (start+limit) of arbitrary data sets.

A Limit is used to process a stream of data while limiting the results to a given window. This window is described by setting the number of items to skip and the maximal number of items to pass on. If the maximal number of items to pass on is null, no limiting will be performed.

This class can be used to "page" through result lists. Having a page size of 25 and showing the 2nd page, would lead to:

 
         Limit limit = new Limit(25,25); // Skip the 25 items of the first page, and show up to 25 items.
         List result = new ArrayList();
         for(Object o : someList) {
             if (limit.nextRow()) {
                 result.add(o);
             }
             // If we already fetched enough items, we can also stop processing further.
             if (!limit.shouldContinue()) {
                 return;
             }
         }
 
 

Field Summary

Fields

Modifier and Type	Field and Description
static Limit	UNLIMITED Represents a limit which has no upper limit and does not skip any items.

Constructor Summary

Constructors

Constructor and Description
Limit(int itemsToSkip, Integer maxItems) Creates a new Limit based on the given parameters.

Method Summary

Modifier and Type	Method and Description
<C> Predicate<C>	asPredicate() Converts the limit into a predicate.
int	getMaxItems() Returns the max number of items or 0 to indicate that there is no upper limit.
Integer	getRemainingItems() Returns the remaining number of items to be processed.
int	getTotalItems() Returns the total number of items to be processed.
boolean	nextRow() Notifies the limit, that the next item is being processed and determines if this is part of the result.
boolean	shouldContinue() Determines if already enough items have been processed or if processing should continue.
static Limit	singleItem() Represents a limit which only accepts the first item.
String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

UNLIMITED

public static final Limit UNLIMITED

Represents a limit which has no upper limit and does not skip any items.

Although a limit is modified internally, we can use a constant here because a unlimited limit has not internal state.

Constructor Detail

Limit

public Limit(int itemsToSkip,
             Integer maxItems)

Creates a new Limit based on the given parameters.

Parameters:

itemsToSkip - denotes the number of items to skip.

maxItems - determines the max number of items. Can be null or 0 to indicate that no limiting is active.

Method Detail

singleItem

public static Limit singleItem()

Represents a limit which only accepts the first item.

Returns:

a new limit which will only accept the first item

nextRow

public boolean nextRow()

Notifies the limit, that the next item is being processed and determines if this is part of the result.

Returns:

true if this item should be output, false otherwise.

shouldContinue

public boolean shouldContinue()

Determines if already enough items have been processed or if processing should continue.

Returns:

true if more items can be used as output, false otherwise

asPredicate

public <C> Predicate<C> asPredicate()

Converts the limit into a predicate.

Note that the limit is stateful and therefore asPredicate should only be called once.

Type Parameters:

C - type used by the stream using this predicate. Ignored as we do not operate on the items itself

Returns:

a predicate implementing the limit

getMaxItems

public int getMaxItems()

Returns the max number of items or 0 to indicate that there is no upper limit.

Returns:

the max. number of items to accept or 0 if there is no upper limit

getTotalItems

public int getTotalItems()

Returns the total number of items to be processed. This is the number of items to be skipped plus the number of items to be accepted. Returns 0 to indicate that there is no upper limit.

Returns:

the total number of items to be processed or 0 if there is no upper limit

getRemainingItems

public Integer getRemainingItems()

Returns the remaining number of items to be processed. This is the number of items to be skipped plus the number of items to be accepted minus the number of items already processed. Returns null to indicate that there is no upper limit.

Returns:

the remaining number of items to be processed or null if there is no upper limit

toString

public String toString()

Overrides:

toString in class Object