org.apache.commons.text

Class StrLookup<V>

java.lang.Object

org.apache.commons.text.StrLookup<V>

public abstract class StrLookup<V>
extends Object

Lookup a String key to a String value.

This class represents the simplest form of a string to string map. It has a benefit over a map in that it can create the result on demand based on the key.

This class comes complete with various factory methods. If these do not suffice, you can subclass and implement your own matcher.

For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value on demand from the database

Since:

1.0

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	StrLookup() Constructor.

Method Summary

Modifier and Type	Method and Description
abstract String	lookup(String key) Looks up a String key to a String value.
static <V> StrLookup<V>	mapLookup(Map<String,V> map) Returns a lookup which looks up values using a map.
static StrLookup<?>	noneLookup() Returns a lookup which always returns null.
static StrLookup<String>	systemPropertiesLookup() Returns a new lookup which uses a copy of the current System properties.

Methods inherited from class java.lang.Object

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

Constructor Detail

StrLookup

protected StrLookup()

Constructor.

Method Detail

noneLookup

public static StrLookup<?> noneLookup()

Returns a lookup which always returns null.

Returns:

a lookup that always returns null, not null

systemPropertiesLookup

public static StrLookup<String> systemPropertiesLookup()

Returns a new lookup which uses a copy of the current System properties.

If a security manager blocked access to system properties, then null will be returned from every lookup.

If a null key is used, this lookup will throw a NullPointerException.

Returns:

a lookup using system properties, not null

mapLookup

public static <V> StrLookup<V> mapLookup(Map<String,V> map)

Returns a lookup which looks up values using a map.

If the map is null, then null will be returned from every lookup. The map result object is converted to a string using toString().

Type Parameters:

V - the type of the values supported by the lookup

Parameters:

map - the map of keys to values, may be null

Returns:

a lookup using the map, not null

lookup

public abstract String lookup(String key)

Looks up a String key to a String value.

The internal implementation may use any mechanism to return the value. The simplest implementation is to use a Map. However, virtually any implementation is possible.

For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value on demand from the database Or, a numeric based implementation could be created that treats the key as an integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.

The lookup(String) method always returns a String, regardless of the underlying data, by converting it as necessary. For example:

 Map<String, Object> map = new HashMap<String, Object>();
 map.put("number", Integer.valueOf(2));
 assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
 

Parameters:

key - the key to be looked up, may be null

Returns:

the matching value, null if no match