Package org.geotools.util

Interface ObjectCache<K,V>

public interface ObjectCache<K,V>

A cache for arbitrary objects. Cache implementations are thread-safe and support concurrency. A cache entry can be locked when an object is in process of being created, but the locking / unlocking must be protected in a try ... finally block.

To use as a reader:

 key = "EPSG:4326";
 CoordinateReferenceSystem crs = cache.get(key);
 

To overwrite:

 cache.put(key, crs);
 

To reserve the entry while figuring out what to write:

 try {
     cache.writeLock(key); // may block if another writer is working on this code.
     value = cache.peek(key);
     if (value == null) {
        // another writer got here first
     } else {
        value = figuringOutWhatToWrite(....);
        cache.put(key, value);
     }
 } finally {
     cache.writeUnLock(key);
 }
 

To use as a proper cache:

 CylindricalCS cs = (CylindricalCS) cache.get(key);
 if (cs == null) {
     try {
         cache.writeLock(key);
         cs = (CylindricalCS) cache.test(key);
         if (cs == null) {
             cs = csAuthority.createCylindricalCS(code);
             cache.put(key, cs);
         }
     } finally {
         cache.writeUnLock(key);
     }
 }
 return cs;
 

Since:

2.5

Author:

Cory Horner (Refractions Research)

Method Summary

Modifier and Type	Method	Description
void	clear()	Removes all entries from this cache.
V	get(K key)	Returns an object from the pool for the specified code.
Set<K>	getKeys()	Returns a set of all the keys currently contained within the ObjectCache.
V	peek(K key)	Use the write lock to test the value for the provided key.
void	put(K key, V object)	Puts an element into the cache.
void	remove(K key)	Removes a given key from the cache.
void	writeLock(K key)	Acquire a write lock on the indicated key.
void	writeUnLock(K key)	Release write lock on the indicated key.

Method Details

clear

void clear()

Removes all entries from this cache.

get

V get(K key)

Returns an object from the pool for the specified code. If the object was retained as a weak reference, the referent is returned.

Parameters:

key - The key whose associated value is to be returned.

peek

V peek(K key)

Use the write lock to test the value for the provided key.

This method is used by a writer to test if someone (ie another writer) has provided the value for us (while we were blocked waiting for them).

Returns:

The value, may be null

put

void put(K key,
 V object)

Puts an element into the cache.

You may simply use this method - it is threadsafe:

 cache.put("4326", crs);
 

You may also consider reserving the entry while you work on the answer:

  try {
     cache.writeLock( "fred" );
     ...find fred
     cache.put( "fred", fred );
  }
  finally {
     cache.writeUnLock();
  }
 

Parameters:

key - the authority code.

object - The referencing object to add in the pool.

writeLock

void writeLock(K key)

Acquire a write lock on the indicated key.

writeUnLock

void writeUnLock(K key)

Release write lock on the indicated key.

getKeys

Set<K> getKeys()

Returns a set of all the keys currently contained within the ObjectCache.

This is a static copy of the keys in the cache at the point in time when the function is called.

Returns:

a set of keys currently contained within the cache.

remove

void remove(K key)

Removes a given key from the cache.