--- /dev/null
+<!-- $Id: overview.html 606716 2007-12-24 17:53:43Z psteitz $ -->
+<html>
+ <head>
+ <title>Overview of the org.apache.commons.pool component</title>
+ </head>
+ <body>
+ <p>
+ Generic Object pooling API with several implementations.
+ </p>
+ <p>
+ The <code>org.apache.commons.pool</code> package defines a simple
+ interface for a pool of object instances, and a handful of base
+ classes that may be useful when creating pool implementations.
+ The API supports pooling of unique objects which can be requested
+ via a key as well as pools where all objects are equivalent.
+ </p>
+ <p>
+ The <code>org.apache.commons.pool.impl</code> package contains
+ several pool implementations.
+ {@link org.apache.commons.pool.impl.StackObjectPool StackObjectPool}
+ is useful for supporting reuse of a limited number of instances while
+ allowing new instances to be created as needed to support high demand.
+ {@link org.apache.commons.pool.impl.GenericObjectPool
+ GenericObjectPool} has many configuration options and can support
+ a limited set of objects such as would be useful in a database
+ connection pool.
+ {@link org.apache.commons.pool.impl.SoftReferenceObjectPool
+ SoftReferenceObjectPool} has no limit on the number of objects in the
+ pool, but the garbage collector can remove idle objects from the pool
+ as needed. There are also keyed versions of the first two.
+ </p>
+ <p>
+ Here is a simple example of pooling <code>HashMap</code>'s. First
+ create an {@link org.apache.commons.pool.ObjectPoolFactory
+ ObjectPoolFactory}
+ </p>
+<pre>
+ public class HashMapFactory
+ extends {@link org.apache.commons.pool.BasePoolableObjectFactory BasePoolableObjectFactory}
+ {
+ /**
+ * Creates an instance that can be returned by the pool.
+ * @return an instance that can be returned by the pool.
+ */
+ public Object makeObject()
+ throws Exception
+ {
+ return new HashMap();
+ }
+
+ /**
+ * Uninitialize an instance to be returned to the pool.
+ * @param obj the instance to be passivated
+ */
+ public void passivateObject(Object obj)
+ throws Exception
+ {
+ Map map = (Map)obj;
+ map.clear();
+ }
+ }
+</pre>
+ <p>
+ A class that makes frequent use of a Map could then use a pool
+ as shown below:
+ </p>
+<pre>
+ public class Foo
+ {
+ private {@link org.apache.commons.pool.ObjectPool ObjectPool} pool;
+ public Foo()
+ {
+ {@link org.apache.commons.pool.PoolableObjectFactory PoolableObjectFactory} factory = new HashMapFactory();
+ pool = new StackObjectPool(factory, 1000);
+ }
+
+ public doSomething()
+ {
+ ...
+ Map map = null;
+ try
+ {
+ map = (Map)pool.borrowObject();
+ // use map
+ ...
+ }
+ finally
+ {
+ if (map != null)
+ {
+ pool.returnObject(map);
+ }
+ }
+ ...
+ }
+ }
+</pre>
+
+<p>
+The above example shows how one would use an
+{@link org.apache.commons.pool.ObjectPool ObjectPool}. The other supplied
+implementations or another special purpose pool would be used similarly.
+</p>
+ </body>
+</html>
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