org.apache.commons.collections
Class ClosureUtils

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

public class ClosureUtils
extends java.lang.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: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $

Author:

Stephen Colebourne, Matt Benson

Constructor Summary

ClosureUtils()
This class is not normally instantiated.

Method Summary

static Closure	asClosure(Transformer transformer) Creates a Closure that calls a Transformer each time it is called.
static Closure	chainedClosure(Closure[] closures) Create a new Closure that calls each closure in turn, passing the result into the next closure.
static Closure	chainedClosure(Closure closure1, Closure closure2) Create a new Closure that calls two Closures, passing the result of the first into the second.
static Closure	chainedClosure(java.util.Collection closures) Create a new Closure that calls each closure in turn, passing the result into the next closure.
static Closure	doWhileClosure(Closure closure, Predicate 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 Closure	forClosure(int count, Closure closure) Creates a Closure that will call the closure count times.
static Closure	ifClosure(Predicate predicate, Closure trueClosure) Create a new Closure that calls another closure based on the result of the specified predicate.
static Closure	ifClosure(Predicate predicate, Closure trueClosure, Closure falseClosure) Create a new Closure that calls one of two closures depending on the specified predicate.
static Closure	invokerClosure(java.lang.String methodName) Creates a Closure that will invoke a specific method on the closure's input object by reflection.
static Closure	invokerClosure(java.lang.String methodName, java.lang.Class[] paramTypes, java.lang.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 Closure	switchClosure(java.util.Map predicatesAndClosures) Create a new Closure that calls one of the closures depending on the predicates.
static Closure	switchClosure(Predicate[] predicates, Closure[] closures) Create a new Closure that calls one of the closures depending on the predicates.
static Closure	switchClosure(Predicate[] predicates, Closure[] closures, Closure defaultClosure) Create a new Closure that calls one of the closures depending on the predicates.
static Closure	switchMapClosure(java.util.Map objectsAndClosures) Create a new Closure that uses the input object as a key to find the closure to call.
static Closure	whileClosure(Predicate predicate, Closure 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 Closure asClosure(Transformer 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 Closure forClosure(int count,
                                 Closure 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 Closure whileClosure(Predicate predicate,
                                   Closure 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:

java.lang.IllegalArgumentException - if either argument is null

See Also:

WhileClosure

doWhileClosure

public static Closure doWhileClosure(Closure closure,
                                     Predicate 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:

java.lang.IllegalArgumentException - if either argument is null

See Also:

WhileClosure

invokerClosure

public static Closure invokerClosure(java.lang.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:

java.lang.IllegalArgumentException - if the method name is null

See Also:

InvokerTransformer, TransformerClosure

invokerClosure

public static Closure invokerClosure(java.lang.String methodName,
                                     java.lang.Class[] paramTypes,
                                     java.lang.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:

java.lang.IllegalArgumentException - if the method name is null

java.lang.IllegalArgumentException - if the paramTypes and args don't match

See Also:

InvokerTransformer, TransformerClosure

chainedClosure

public static Closure chainedClosure(Closure closure1,
                                     Closure 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:

java.lang.IllegalArgumentException - if either closure is null

See Also:

ChainedClosure

chainedClosure

public static Closure chainedClosure(Closure[] 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:

java.lang.IllegalArgumentException - if the closures array is null

java.lang.IllegalArgumentException - if any closure in the array is null

See Also:

ChainedClosure

chainedClosure

public static Closure chainedClosure(java.util.Collection 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:

java.lang.IllegalArgumentException - if the closures collection is null

java.lang.IllegalArgumentException - if the closures collection is empty

java.lang.IllegalArgumentException - if any closure in the collection is null

See Also:

ChainedClosure

ifClosure

public static Closure ifClosure(Predicate predicate,
                                Closure trueClosure)

Create a new Closure that calls another closure based on the result of the specified predicate.

Parameters:

predicate - the validating predicate

trueClosure - the closure called if the predicate is true

Returns:

the if closure

Throws:

java.lang.IllegalArgumentException - if the predicate is null

java.lang.IllegalArgumentException - if the closure is null

Since:

Commons Collections 3.2

See Also:

IfClosure

ifClosure

public static Closure ifClosure(Predicate predicate,
                                Closure trueClosure,
                                Closure 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:

java.lang.IllegalArgumentException - if the predicate is null

java.lang.IllegalArgumentException - if either closure is null

See Also:

IfClosure

switchClosure

public static Closure switchClosure(Predicate[] predicates,
                                    Closure[] 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:

java.lang.IllegalArgumentException - if the either array is null

java.lang.IllegalArgumentException - if any element in the arrays is null

java.lang.IllegalArgumentException - if the arrays are different sizes

See Also:

SwitchClosure

switchClosure

public static Closure switchClosure(Predicate[] predicates,
                                    Closure[] closures,
                                    Closure 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:

java.lang.IllegalArgumentException - if the either array is null

java.lang.IllegalArgumentException - if any element in the arrays is null

java.lang.IllegalArgumentException - if the arrays are different sizes

See Also:

SwitchClosure

switchClosure

public static Closure switchClosure(java.util.Map 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:

java.lang.IllegalArgumentException - if the map is null

java.lang.IllegalArgumentException - if the map is empty

java.lang.IllegalArgumentException - if any closure in the map is null

java.lang.ClassCastException - if the map elements are of the wrong type

See Also:

SwitchClosure

switchMapClosure

public static Closure switchMapClosure(java.util.Map 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:

java.lang.IllegalArgumentException - if the map is null

java.lang.IllegalArgumentException - if the map is empty

java.lang.IllegalArgumentException - if any closure in the map is null

See Also:

SwitchClosure