org.apache.commons.collections
Class ClosureUtils

java.lang.Object
  org.apache.commons.collections.ClosureUtils

public class ClosureUtils
extends Object

ClosureUtils provides reference implementations and utilities for the Closure functor interface. The supplied closures are:

• Invoker - invokes a method on the input object
• For - repeatedly calls a closure for a fixed number of times
• While - repeatedly calls a closure while a predicate is true
• DoWhile - repeatedly calls a closure while a predicate is true
• Chained - chains two or more closures together
• Switch - calls one closure based on one or more predicates
• SwitchMap - calls one closure looked up from a Map
• Transformer - wraps a Transformer as a Closure
• NOP - does nothing
• Exception - always throws an exception

All the supplied closures are Serializable.

Since:

Commons Collections 3.0

Version:

$Revision: 1.1.1.1 $ $Date: 2005/05/23 04:32:43 $

Author:

Matt Hall, John Watkinson, Stephen Colebourne

Constructor Summary

ClosureUtils()
This class is not normally instantiated.

Method Summary

static <I,O> Closure<I>	asClosure(Transformer<I,O> transformer) Creates a Closure that calls a Transformer each time it is called.
static <T> Closure<T>	chainedClosure(Closure<T>[] closures) Create a new Closure that calls each closure in turn, passing the result into the next closure.
static <T> Closure<T>	chainedClosure(Closure<T> closure1, Closure<T> closure2) Create a new Closure that calls two Closures, passing the result of the first into the second.
static <T> Closure<T>	chainedClosure(Collection<T> closures) Create a new Closure that calls each closure in turn, passing the result into the next closure.
static <T> Closure<T>	doWhileClosure(Closure<? super T> closure, Predicate<? super T> predicate) Creates a Closure that will call the closure once and then repeatedly until the predicate returns false.
static Closure	exceptionClosure() Gets a Closure that always throws an exception.
static <T> Closure<T>	forClosure(int count, Closure<T> closure) Creates a Closure that will call the closure count times.
static <T> Closure<T>	ifClosure(Predicate<? super T> predicate, Closure<? super T> trueClosure, Closure<? super T> falseClosure) Create a new Closure that calls one of two closures depending on the specified predicate.
static Closure	invokerClosure(String methodName) Creates a Closure that will invoke a specific method on the closure's input object by reflection.
static Closure	invokerClosure(String methodName, Class[] paramTypes, Object[] args) Creates a Closure that will invoke a specific method on the closure's input object by reflection.
static Closure	nopClosure() Gets a Closure that will do nothing.
static <T> Closure<T>	switchClosure(Map<Predicate<? super T>,Closure<? super T>> predicatesAndClosures) Create a new Closure that calls one of the closures depending on the predicates.
static <T> Closure<T>	switchClosure(Predicate<? super T>[] predicates, Closure<? super T>[] closures) Create a new Closure that calls one of the closures depending on the predicates.
static <T> Closure<T>	switchClosure(Predicate<? super T>[] predicates, Closure<? super T>[] closures, Closure<? super T> defaultClosure) Create a new Closure that calls one of the closures depending on the predicates.
static <T> Closure<T>	switchMapClosure(Map<T,Closure<T>> objectsAndClosures) Create a new Closure that uses the input object as a key to find the closure to call.
static <T> Closure<T>	whileClosure(Predicate<? super T> predicate, Closure<? super T> closure) Creates a Closure that will call the closure repeatedly until the predicate returns false.

Methods inherited from class java.lang.Object

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

Constructor Detail

ClosureUtils

public ClosureUtils()

This class is not normally instantiated.

Method Detail

exceptionClosure

public static Closure exceptionClosure()

Gets a Closure that always throws an exception. This could be useful during testing as a placeholder.

Returns:

the closure

See Also:

ExceptionClosure

nopClosure

public static Closure nopClosure()

Gets a Closure that will do nothing. This could be useful during testing as a placeholder.

Returns:

the closure

See Also:

NOPClosure

asClosure

public static <I,O> Closure<I> asClosure(Transformer<I,O> transformer)

Creates a Closure that calls a Transformer each time it is called. The transformer will be called using the closure's input object. The transformer's result will be ignored.

Parameters:

transformer - the transformer to run each time in the closure, null means nop

Returns:

the closure

See Also:

TransformerClosure

forClosure

public static <T> Closure<T> forClosure(int count,
                                        Closure<T> closure)

Creates a Closure that will call the closure count times.

A null closure or zero count returns the NOPClosure.

Parameters:

count - the number of times to loop

closure - the closure to call repeatedly

Returns:

the for closure

See Also:

ForClosure

whileClosure

public static <T> Closure<T> whileClosure(Predicate<? super T> predicate,
                                          Closure<? super T> closure)

Creates a Closure that will call the closure repeatedly until the predicate returns false.

Parameters:

predicate - the predicate to use as an end of loop test, not null

closure - the closure to call repeatedly, not null

Returns:

the while closure

Throws:

IllegalArgumentException - if either argument is null

See Also:

WhileClosure

doWhileClosure

public static <T> Closure<T> doWhileClosure(Closure<? super T> closure,
                                            Predicate<? super T> predicate)

Creates a Closure that will call the closure once and then repeatedly until the predicate returns false.

Parameters:

closure - the closure to call repeatedly, not null

predicate - the predicate to use as an end of loop test, not null

Returns:

the do-while closure

Throws:

IllegalArgumentException - if either argument is null

See Also:

WhileClosure

invokerClosure

public static Closure invokerClosure(String methodName)

Creates a Closure that will invoke a specific method on the closure's input object by reflection.

Parameters:

methodName - the name of the method

Returns:

the invoker closure

Throws:

IllegalArgumentException - if the method name is null

See Also:

InvokerTransformer, TransformerClosure

invokerClosure

public static Closure invokerClosure(String methodName,
                                     Class[] paramTypes,
                                     Object[] args)

Creates a Closure that will invoke a specific method on the closure's input object by reflection.

Parameters:

methodName - the name of the method

paramTypes - the parameter types

args - the arguments

Returns:

the invoker closure

Throws:

IllegalArgumentException - if the method name is null

IllegalArgumentException - if the paramTypes and args don't match

See Also:

InvokerTransformer, TransformerClosure

chainedClosure

public static <T> Closure<T> chainedClosure(Closure<T> closure1,
                                            Closure<T> closure2)

Create a new Closure that calls two Closures, passing the result of the first into the second.

Parameters:

closure1 - the first closure

closure2 - the second closure

Returns:

the chained closure

Throws:

IllegalArgumentException - if either closure is null

See Also:

ChainedClosure

chainedClosure

public static <T> Closure<T> chainedClosure(Closure<T>[] closures)

Create a new Closure that calls each closure in turn, passing the result into the next closure.

Parameters:

closures - an array of closures to chain

Returns:

the chained closure

Throws:

IllegalArgumentException - if the closures array is null

IllegalArgumentException - if any closure in the array is null

See Also:

ChainedClosure

chainedClosure

public static <T> Closure<T> chainedClosure(Collection<T> closures)

Create a new Closure that calls each closure in turn, passing the result into the next closure. The ordering is that of the iterator() method on the collection.

Parameters:

closures - a collection of closures to chain

Returns:

the chained closure

Throws:

IllegalArgumentException - if the closures collection is null

IllegalArgumentException - if the closures collection is empty

IllegalArgumentException - if any closure in the collection is null

See Also:

ChainedClosure

ifClosure

public static <T> Closure<T> ifClosure(Predicate<? super T> predicate,
                                       Closure<? super T> trueClosure,
                                       Closure<? super T> falseClosure)

Create a new Closure that calls one of two closures depending on the specified predicate.

Parameters:

predicate - the predicate to switch on

trueClosure - the closure called if the predicate is true

falseClosure - the closure called if the predicate is false

Returns:

the switch closure

Throws:

IllegalArgumentException - if the predicate is null

IllegalArgumentException - if either closure is null

See Also:

IfClosure

switchClosure

public static <T> Closure<T> switchClosure(Predicate<? super T>[] predicates,
                                           Closure<? super T>[] closures)

Create a new Closure that calls one of the closures depending on the predicates.

The closure at array location 0 is called if the predicate at array location 0 returned true. Each predicate is evaluated until one returns true.

Parameters:

predicates - an array of predicates to check, not null

closures - an array of closures to call, not null

Returns:

the switch closure

Throws:

IllegalArgumentException - if the either array is null

IllegalArgumentException - if any element in the arrays is null

IllegalArgumentException - if the arrays are different sizes

See Also:

SwitchClosure

switchClosure

public static <T> Closure<T> switchClosure(Predicate<? super T>[] predicates,
                                           Closure<? super T>[] closures,
                                           Closure<? super T> defaultClosure)

Create a new Closure that calls one of the closures depending on the predicates.

The closure at array location 0 is called if the predicate at array location 0 returned true. Each predicate is evaluated until one returns true. If no predicates evaluate to true, the default closure is called.

Parameters:

predicates - an array of predicates to check, not null

closures - an array of closures to call, not null

defaultClosure - the default to call if no predicate matches

Returns:

the switch closure

Throws:

IllegalArgumentException - if the either array is null

IllegalArgumentException - if any element in the arrays is null

IllegalArgumentException - if the arrays are different sizes

See Also:

SwitchClosure

switchClosure

public static <T> Closure<T> switchClosure(Map<Predicate<? super T>,Closure<? super T>> predicatesAndClosures)

Create a new Closure that calls one of the closures depending on the predicates.

The Map consists of Predicate keys and Closure values. A closure is called if its matching predicate returns true. Each predicate is evaluated until one returns true. If no predicates evaluate to true, the default closure is called. The default closure is set in the map with a null key. The ordering is that of the iterator() method on the entryset collection of the map.

Parameters:

predicatesAndClosures - a map of predicates to closures

Returns:

the switch closure

Throws:

IllegalArgumentException - if the map is null

IllegalArgumentException - if the map is empty

IllegalArgumentException - if any closure in the map is null

ClassCastException - if the map elements are of the wrong type

See Also:

SwitchClosure

switchMapClosure

public static <T> Closure<T> switchMapClosure(Map<T,Closure<T>> objectsAndClosures)

Create a new Closure that uses the input object as a key to find the closure to call.

The Map consists of object keys and Closure values. A closure is called if the input object equals the key. If there is no match, the default closure is called. The default closure is set in the map using a null key.

Parameters:

objectsAndClosures - a map of objects to closures

Returns:

the closure

Throws:

IllegalArgumentException - if the map is null

IllegalArgumentException - if the map is empty

IllegalArgumentException - if any closure in the map is null

See Also:

SwitchClosure