org.geotools.util

Interface ObjectCache

public interface ObjectCache

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)

See Also:

https://jsr-107-interest.dev.java.net/javadoc/javax/cache/package-summary.html

Method Summary

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

Method Detail

clear

void clear()

Removes all entries from this cache.

get

Object get(Object 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

Object peek(Object 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(Object key,
         Object 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(Object key)

Acquire a write lock on the indicated key.

writeUnLock

void writeUnLock(Object key)

Release write lock on the indicated key.

getKeys

Set<Object> 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(Object key)

Removes a given key from the cache.