com.dtolabs.utils

Class Mapper

java.lang.Object

com.dtolabs.utils.Mapper

public abstract class Mapper
extends java.lang.Object

Some basic functions from other languages just don't exist in java :)
This utility class provides simple methods for "mapping" a set of objects to a new set of objects, based on a provided implementation.
The mapping will be one to one, although if the result of a particular mapping returns null, the result can be discarded (default) rather than included.
Each static utility method which by default ignores null results has an equivalent method which has a boolean parameter indicating whether nulls should be discarded or not.
The other use for this utility class is to perform the same action on all items of a collection, where no result is necessarily returned or important.
Example usage:

 //create a collection of Strings from some objects
 Collection c = Mapper.map(new Mapper(){
      public Object map(Object o){
          return o.toString();
      }, someIterator);
 

 

 //simply perform some action and discard the results
 Mapper.map(new Mapper(){
      public Object map(Object o){
          ((MyTaskThread)o).performTask();
          return null;
      }, someIterator);
 

Field Summary

Fields

Modifier and Type	Field and Description
static Mapper	identity Maps an object to itself.
static Mapper	toString Maps an object to the results of the toString() method.

Constructor Summary

Constructors

Constructor and Description
Mapper()

Method Summary

Modifier and Type	Method and Description
java.util.Collection	apply(java.util.Collection c)
java.util.Collection	apply(java.util.Enumeration en)
java.util.Collection	apply(java.util.Iterator i)
java.util.Collection	apply(java.lang.Object[] arr)
java.util.Map	applyToEntries(java.util.Map map)
java.util.Map	applyToKeys(java.util.Map map)
java.util.Map	applyToValues(java.util.Map map)
static java.util.Collection	beanMap(java.lang.String property, java.util.Collection c) Map dynamically using a bean property name.
static java.util.Collection	beanMap(java.lang.String property, java.util.Collection c, boolean includeNull) Map dynamically using a bean property name.
static java.util.Collection	beanMap(java.lang.String property, java.util.Iterator i) Map dynamically using a bean property name.
static java.util.Collection	beanMap(java.lang.String property, java.util.Iterator i, boolean includeNull) Map dynamically using a bean property name.
static java.util.Collection	beanMap(java.lang.String property, java.lang.Object[] objs) Map dynamically using a bean property name.
static Mapper	beanMapper(java.lang.String property) Create a mapper for bean properties
static java.util.Comparator	comparator(Mapper mapper) Create a Comparator which compares two objects by first mapping each object with a mapper and then comparing the result objects.
static java.util.Comparator	comparator(Mapper mapper, boolean reverse) see comparator(Mapper)
Mapper	concat(Mapper mapper) Concatenate another mapper onto this one.
static Mapper	concat(Mapper[] arr) Concatenate more than two Mappers.
static Mapper	concat(Mapper first, Mapper second) Concatenate two Mappers.
static Mapper	filterMapper(org.apache.commons.collections.Predicate pred) Return a mapper than maps an object to itself if the predicate evaluates to true, and to null otherwise.
java.util.Map	makeMap(java.util.Collection c)
java.util.Map	makeMap(java.util.Enumeration en)
java.util.Map	makeMap(java.util.Iterator i)
static java.util.Map	makeMap(Mapper mapper, java.util.Collection c) Create a new Map by using the collection objects as keys, and the mapping result as values.
static java.util.Map	makeMap(Mapper mapper, java.util.Collection c, boolean includeNull) Create a new Map by using the collection objects as keys, and the mapping result as values.
static java.util.Map	makeMap(Mapper mapper, java.util.Enumeration en) Create a new Map by using the enumeration objects as keys, and the mapping result as values.
static java.util.Map	makeMap(Mapper mapper, java.util.Enumeration en, boolean includeNull) Create a new Map by using the enumeration objects as keys, and the mapping result as values.
static java.util.Map	makeMap(Mapper mapper, java.util.Iterator i) Create a new Map by using the iterator objects as keys, and the mapping result as values.
static java.util.Map	makeMap(Mapper mapper, java.util.Iterator i, boolean includeNull) Create a new Map by using the iterator objects as keys, and the mapping result as values.
static java.util.Map	makeMap(Mapper mapper, java.lang.Object[] a) Create a new Map by using the array objects as keys, and the mapping result as values.
static java.util.Map	makeMap(Mapper mapper, java.lang.Object[] a, boolean includeNull) Create a new Map by using the array objects as keys, and the mapping result as values.
java.util.Map	makeMap(java.lang.Object[] a)
static java.util.Collection	map(Mapper mapper, java.util.Collection c) Return the results of mapping all objects with the mapper.
static java.util.Collection	map(Mapper mapper, java.util.Collection c, boolean allowNull) Return the results of mapping all objects with the mapper.
static java.util.Collection	map(Mapper mapper, java.util.Enumeration en) Return the results of mapping all objects with the mapper.
static java.util.Collection	map(Mapper mapper, java.util.Enumeration en, boolean allowNull) Return the results of mapping all objects with the mapper.
static java.util.Collection	map(Mapper mapper, java.util.Iterator i) Return the results of mapping all objects with the mapper.
static java.util.Collection	map(Mapper mapper, java.util.Iterator i, boolean includeNull) Return the results of mapping all objects with the mapper.
static java.util.Collection	map(Mapper mapper, java.lang.Object o) Trivial case of a single object.
static java.util.Collection	map(Mapper mapper, java.lang.Object[] arr) Return the results of mapping all objects with the mapper.
static java.util.Collection	map(Mapper mapper, java.lang.Object[] arr, boolean allowNull) Return the results of mapping all objects with the mapper.
abstract java.lang.Object	map(java.lang.Object a) Map one object to another.
static java.util.Map	mapEntries(Mapper mapper, java.util.Map map) Create a new Map by mapping all values from the original map and mapping all keys.
static java.util.Map	mapEntries(Mapper mapper, java.util.Map map, boolean includeNull) Create a new Map by mapping all values from the original map, and mapping all keys.
static java.util.Map	mapKeys(Mapper mapper, java.util.Map map) Create a new Map by mapping all keys from the original map and maintaining the original value.
static java.util.Map	mapKeys(Mapper mapper, java.util.Map map, boolean allowNull) Create a new Map by mapping all keys from the original map and maintaining the original value.
static Mapper	mapMapper(java.util.Map map) Return a mapper that uses a Map instance, and maps keys of that Map to the values.
static java.util.Map	mapValues(Mapper mapper, java.util.Map map) Create a new Map by mapping all values from the original map and maintaining the original key.
static java.util.Map	mapValues(Mapper mapper, java.util.Map map, boolean includeNull) Create a new Map by mapping all values from the original map and maintaining the original key.
static Mapper	uniqueMapper()
static java.util.Map	zip(java.util.Iterator keys, java.util.Iterator values) Creates a map where the object at index N from the first Iterator is the key for the object at index N of the second Iterator.
static java.util.Map	zip(java.util.Iterator keys, java.util.Iterator values, boolean includeNull) Creates a map where the object at index N from the first Iterator is the key for the object at index N of the second Iterator.
static java.util.Map	zip(java.util.List keys, java.util.List values) Creates a map where the object at index N from the first List is the key for the object at index N of the second List.
static java.util.Map	zip(java.util.List keys, java.util.List values, boolean includeNull) Creates a map where the object at index N from the first List is the key for the object at index N of the second List.
static java.util.Map	zip(java.lang.Object[] keys, java.lang.Object[] values) Creates a map where the object at index N from the first Iterator is the key for the object at index N of the second Iterator.
static java.util.Map	zip(java.lang.Object[] keys, java.lang.Object[] values, boolean includeNull) Creates a map where the object at index N from the first Iterator is the key for the object at index N of the second Iterator.

Methods inherited from class java.lang.Object

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

Field Detail

toString

public static final Mapper toString

Maps an object to the results of the toString() method.

identity

public static final Mapper identity

Maps an object to itself.

Constructor Detail

Mapper

public Mapper()

Method Detail

comparator

public static java.util.Comparator comparator(Mapper mapper)

Create a Comparator which compares two objects by first mapping each object with a mapper and then comparing the result objects. Note: The Mapper instance must map every object into one that implements the Comparable interface, otherwise the two objects cannot be compared. (All of the java.lang.* wrapper types will work.)

Parameters:

mapper - mapper

Returns:

comparator

comparator

public static java.util.Comparator comparator(Mapper mapper,
                                              boolean reverse)

see comparator(Mapper)

Parameters:

mapper - mapper

reverse - if true, reverse the order of comparison

Returns:

comparator

concat

public Mapper concat(Mapper mapper)

Concatenate another mapper onto this one.

Parameters:

mapper - mapper

Returns:

mapper

concat

public static Mapper concat(Mapper[] arr)

Concatenate more than two Mappers.

Parameters:

arr - array of Mapper instances. a null array will return the identity Mapper.

Returns:

single Mapper concatenating the Mappers.

concat

public static Mapper concat(Mapper first,
                            Mapper second)

Concatenate two Mappers.

Parameters:

first - first mapper to apply

second - second mapper to apply

Returns:

mapper

zip

public static java.util.Map zip(java.util.List keys,
                                java.util.List values)

Creates a map where the object at index N from the first List is the key for the object at index N of the second List.
By default discards both key and value if either one is null.

Parameters:

keys - List of keys

values - List of values

Returns:

map

zip

public static java.util.Map zip(java.util.List keys,
                                java.util.List values,
                                boolean includeNull)

Creates a map where the object at index N from the first List is the key for the object at index N of the second List. If either List is shorter than the other, the resulting Map will have only as many keys as are in the smallest of the two Lists.
If includeNull is true, both keys and values of null are allowed. Note that if more than one key is null, previous entries will be overwritten.

Parameters:

keys - List of keys

values - List of values

includeNull - allow null values and keys

Returns:

map

zip

public static java.util.Map zip(java.lang.Object[] keys,
                                java.lang.Object[] values)

Creates a map where the object at index N from the first Iterator is the key for the object at index N of the second Iterator.
By default discards both key and value if either one is null.

Parameters:

keys - array of keys

values - array of values

Returns:

map

zip

public static java.util.Map zip(java.lang.Object[] keys,
                                java.lang.Object[] values,
                                boolean includeNull)

Creates a map where the object at index N from the first Iterator is the key for the object at index N of the second Iterator. If either Iterator is shorter than the other, the resulting Map will have only as many keys as are in the smallest of the two Iterator.
If includeNull is true, both keys and values of null are allowed. Note that if more than one key is null, previous entries will be overwritten.

Parameters:

keys - array of keys

values - array of values

includeNull - allow null values and keys

Returns:

map

zip

public static java.util.Map zip(java.util.Iterator keys,
                                java.util.Iterator values)

Creates a map where the object at index N from the first Iterator is the key for the object at index N of the second Iterator.
By default discards both key and value if either one is null.

Parameters:

keys - Iterator of keys

values - Iterator of values

Returns:

map

zip

public static java.util.Map zip(java.util.Iterator keys,
                                java.util.Iterator values,
                                boolean includeNull)

Creates a map where the object at index N from the first Iterator is the key for the object at index N of the second Iterator. If either Iterator is shorter than the other, the resulting Map will have only as many keys as are in the smallest of the two Iterator.
If includeNull is true, both keys and values of null are allowed. Note that if more than one key is null, previous entries will be overwritten.

Parameters:

keys - Iterator of keys

values - Iterator of values

includeNull - allow null values and keys

Returns:

map

map

public static java.util.Collection map(Mapper mapper,
                                       java.lang.Object o)

Trivial case of a single object.

Parameters:

mapper - an Mapper

o - an Object

Returns:

a Collection of the results.

map

public static java.util.Collection map(Mapper mapper,
                                       java.util.Collection c)

Return the results of mapping all objects with the mapper.

Parameters:

mapper - an Mapper

c - a Collection

Returns:

a Collection of the results.

apply

public java.util.Collection apply(java.util.Collection c)

map

public static java.util.Collection map(Mapper mapper,
                                       java.util.Collection c,
                                       boolean allowNull)

Return the results of mapping all objects with the mapper.

Parameters:

mapper - an Mapper

c - a Collection

allowNull - allow null values

Returns:

a Collection of the results.

map

public static java.util.Collection map(Mapper mapper,
                                       java.lang.Object[] arr)

Return the results of mapping all objects with the mapper.

Parameters:

mapper - an Mapper

arr - an array of objects

Returns:

a Collection of the results.

apply

public java.util.Collection apply(java.lang.Object[] arr)

map

public static java.util.Collection map(Mapper mapper,
                                       java.lang.Object[] arr,
                                       boolean allowNull)

Return the results of mapping all objects with the mapper.

Parameters:

mapper - an Mapper

arr - an array of objects

allowNull - allow null values

Returns:

a Collection of the results.

map

public static java.util.Collection map(Mapper mapper,
                                       java.util.Enumeration en)

Return the results of mapping all objects with the mapper.

Parameters:

mapper - an Mapper

en - an Enumeration

Returns:

a Collection of the results.

apply

public java.util.Collection apply(java.util.Enumeration en)

map

public static java.util.Collection map(Mapper mapper,
                                       java.util.Enumeration en,
                                       boolean allowNull)

Return the results of mapping all objects with the mapper.

Parameters:

mapper - an Mapper

en - an Enumeration

allowNull - allow null values

Returns:

a Collection of the results.

mapKeys

public static java.util.Map mapKeys(Mapper mapper,
                                    java.util.Map map)

Create a new Map by mapping all keys from the original map and maintaining the original value.

Parameters:

mapper - a Mapper to map the keys

map - a Map

Returns:

a new Map with keys mapped

applyToKeys

public java.util.Map applyToKeys(java.util.Map map)

mapKeys

public static java.util.Map mapKeys(Mapper mapper,
                                    java.util.Map map,
                                    boolean allowNull)

Create a new Map by mapping all keys from the original map and maintaining the original value.

Parameters:

mapper - a Mapper to map the keys

map - a Map

allowNull - allow null values

Returns:

a new Map with keys mapped

mapValues

public static java.util.Map mapValues(Mapper mapper,
                                      java.util.Map map)

Create a new Map by mapping all values from the original map and maintaining the original key.

Parameters:

mapper - a Mapper to map the values

map - an Map

Returns:

a new Map with values mapped

applyToValues

public java.util.Map applyToValues(java.util.Map map)

mapValues

public static java.util.Map mapValues(Mapper mapper,
                                      java.util.Map map,
                                      boolean includeNull)

Create a new Map by mapping all values from the original map and maintaining the original key.

Parameters:

mapper - a Mapper to map the values

map - an Map

includeNull - true to include null

Returns:

a new Map with values mapped

mapEntries

public static java.util.Map mapEntries(Mapper mapper,
                                       java.util.Map map)

Create a new Map by mapping all values from the original map and mapping all keys.

Parameters:

mapper - a Mapper to map the values and keys

map - a Map

Returns:

a new Map with values mapped

applyToEntries

public java.util.Map applyToEntries(java.util.Map map)

mapEntries

public static java.util.Map mapEntries(Mapper mapper,
                                       java.util.Map map,
                                       boolean includeNull)

Create a new Map by mapping all values from the original map, and mapping all keys.

Parameters:

mapper - a Mapper to map both values and keys

map - Map input

includeNull - if true, allow null as either key or value after mapping

Returns:

a new Map with both keys and values mapped using the Mapper

makeMap

public static java.util.Map makeMap(Mapper mapper,
                                    java.lang.Object[] a)

Create a new Map by using the array objects as keys, and the mapping result as values. Discard keys which return null values from the mapper.

Parameters:

mapper - a Mapper to map the values

a - array of items

Returns:

a new Map with values mapped

makeMap

public java.util.Map makeMap(java.lang.Object[] a)

makeMap

public static java.util.Map makeMap(Mapper mapper,
                                    java.lang.Object[] a,
                                    boolean includeNull)

Create a new Map by using the array objects as keys, and the mapping result as values.

Parameters:

mapper - a Mapper to map the values

a - array of items

includeNull - true to include null

Returns:

a new Map with values mapped

makeMap

public static java.util.Map makeMap(Mapper mapper,
                                    java.util.Collection c)

Create a new Map by using the collection objects as keys, and the mapping result as values. Discard keys which return null values from the mapper.

Parameters:

mapper - a Mapper to map the values

c - Collection of items

Returns:

a new Map with values mapped

makeMap

public java.util.Map makeMap(java.util.Collection c)

makeMap

public static java.util.Map makeMap(Mapper mapper,
                                    java.util.Collection c,
                                    boolean includeNull)

Create a new Map by using the collection objects as keys, and the mapping result as values.

Parameters:

mapper - a Mapper to map the values

c - Collection of items

includeNull - true to include null

Returns:

a new Map with values mapped

makeMap

public static java.util.Map makeMap(Mapper mapper,
                                    java.util.Iterator i)

Create a new Map by using the iterator objects as keys, and the mapping result as values. Discard keys which return null values from the mapper.

Parameters:

mapper - a Mapper to map the values

i - Iterator

Returns:

a new Map with values mapped

makeMap

public java.util.Map makeMap(java.util.Iterator i)

makeMap

public static java.util.Map makeMap(Mapper mapper,
                                    java.util.Iterator i,
                                    boolean includeNull)

Create a new Map by using the iterator objects as keys, and the mapping result as values.

Parameters:

mapper - a Mapper to map the values

i - Iterator

includeNull - true to include null

Returns:

a new Map with values mapped

makeMap

public static java.util.Map makeMap(Mapper mapper,
                                    java.util.Enumeration en)

Create a new Map by using the enumeration objects as keys, and the mapping result as values. Discard keys which return null values from the mapper.

Parameters:

mapper - a Mapper to map the values

en - Enumeration

Returns:

a new Map with values mapped

makeMap

public java.util.Map makeMap(java.util.Enumeration en)

makeMap

public static java.util.Map makeMap(Mapper mapper,
                                    java.util.Enumeration en,
                                    boolean includeNull)

Create a new Map by using the enumeration objects as keys, and the mapping result as values.

Parameters:

mapper - a Mapper to map the values

en - Enumeration

includeNull - true to include null

Returns:

a new Map with values mapped

map

public static java.util.Collection map(Mapper mapper,
                                       java.util.Iterator i)

Return the results of mapping all objects with the mapper.

Parameters:

mapper - an Mapper

i - an Iterator

Returns:

a Collection of the results.

apply

public java.util.Collection apply(java.util.Iterator i)

map

public static java.util.Collection map(Mapper mapper,
                                       java.util.Iterator i,
                                       boolean includeNull)

Return the results of mapping all objects with the mapper.

Parameters:

mapper - an Mapper

i - an Iterator

includeNull - specify whether nulls are included

Returns:

a Collection of the results.

beanMap

public static java.util.Collection beanMap(java.lang.String property,
                                           java.lang.Object[] objs)

Map dynamically using a bean property name.

Parameters:

property - the name of a bean property

objs - an array of objects

Returns:

collection

Throws:

java.lang.ClassCastException - if there is an error invoking the method on any object.

beanMap

public static java.util.Collection beanMap(java.lang.String property,
                                           java.util.Iterator i)

Map dynamically using a bean property name.

Parameters:

property - the name of a bean property

i - an iterator of objects

Returns:

collection

Throws:

java.lang.ClassCastException - if there is an error invoking the method on any object.

beanMap

public static java.util.Collection beanMap(java.lang.String property,
                                           java.util.Collection c,
                                           boolean includeNull)

Map dynamically using a bean property name.

Parameters:

property - the name of a bean property

c - an Collection of objects

includeNull - true to include null results in the response

Returns:

collection

Throws:

java.lang.ClassCastException - if there is an error invoking the method on any object.

beanMap

public static java.util.Collection beanMap(java.lang.String property,
                                           java.util.Collection c)

Map dynamically using a bean property name.

Parameters:

property - the name of a bean property

c - a collection of objects

Returns:

collection

Throws:

java.lang.ClassCastException - if there is an error invoking the method on any object.

beanMapper

public static Mapper beanMapper(java.lang.String property)

Create a mapper for bean properties

Parameters:

property - name of the bean property

Returns:

mapper

beanMap

public static java.util.Collection beanMap(java.lang.String property,
                                           java.util.Iterator i,
                                           boolean includeNull)

Map dynamically using a bean property name.

Parameters:

property - the name of a bean property

i - an iterator of objects

includeNull - true to include null results in the response

Returns:

collection

Throws:

java.lang.ClassCastException - if there is an error invoking the method on any object.

filterMapper

public static Mapper filterMapper(org.apache.commons.collections.Predicate pred)

Return a mapper than maps an object to itself if the predicate evaluates to true, and to null otherwise.

Parameters:

pred - predicate

Returns:

mapper

uniqueMapper

public static Mapper uniqueMapper()

Returns:

a mapper that maps unique objects to themselves, and duplicates to null.

mapMapper

public static Mapper mapMapper(java.util.Map map)

Return a mapper that uses a Map instance, and maps keys of that Map to the values.

Parameters:

map - a Map instance

Returns:

a Mapper instance

map

public abstract java.lang.Object map(java.lang.Object a)

Map one object to another.

Parameters:

a - object

Returns:

the new object.