public abstract class StrLookup<V> extends Object
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
| Modifier | Constructor and Description |
|---|---|
protected |
StrLookup()
Constructor.
|
| 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. |
public static StrLookup<?> noneLookup()
public static StrLookup<String> systemPropertiesLookup()
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.
public static <V> StrLookup<V> mapLookup(Map<String,V> 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().
V - the type of the values supported by the lookupmap - the map of keys to values, may be nullpublic abstract String lookup(String key)
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"));
key - the key to be looked up, may be null