src/site/xdoc/examples.xml (154 lines of code) (raw):
<?xml version="1.0"?>
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<document>
<properties>
<title>Examples</title>
<author email="dev@commons.apache.org">Apache Commons Documentation Team</author>
<revision>$Id$</revision>
</properties>
<body>
<section name="A Simple Pool Client">
<p>
Suppose you're writing a set of <code>java.io.Reader</code> utilities, and would like to
provide a method for dumping the contents of a <code>Reader</code> to a <code>String</code>.
Here's the code for the <code>ReaderUtil</code>, implemented without an <code>ObjectPool</code>:
</p>
<source>
import java.io.Reader;
import java.io.IOException;
public class ReaderUtil {
public ReaderUtil() {
}
/**
* Dumps the contents of the {@link Reader} to a
* String, closing the {@link Reader} when done.
*/
public String readToString(Reader in) throws IOException {
StringBuffer buf = new StringBuffer();
try {
for(int c = in.read(); c != -1; c = in.read()) {
buf.append((char)c);
}
return buf.toString();
} catch(IOException e) {
throw e;
} finally {
try {
in.close();
} catch(Exception e) {
// ignored
}
}
}
}
</source>
<p>
For the sake of this example, let's assume we want to pool the <code>StringBuffer</code>s
used to buffer the <code>Reader</code>'s contents. (A pool of <code>StringBuffer</code>s
may or may not be useful in practice. We're just using it as a simple example here.)
</p>
<p>
Let's further assume that a complete pool implementation will be provided via
a constructor. (We'll show you how to create such an implementation in just a moment.)
Then to use the pool we simply call <code>borrowObject</code> to obtain the buffer, and
then call <code>returnObject</code> when we're done with it.
Then a <code>ReaderUtil</code> implementation using a pool of <code>StringBuffer</code>s might look
like this:
</p>
<source>
import java.io.IOException;
import java.io.Reader;
import org.apache.commons.pool3.ObjectPool;
public class ReaderUtil {
private ObjectPool<StringBuffer> pool;
public ReaderUtil(ObjectPool<StringBuffer> pool) {
this.pool = pool;
}
/**
* Dumps the contents of the {@link Reader} to a String, closing the {@link Reader} when done.
*/
public String readToString(Reader in)
throws IOException {
StringBuffer buf = null;
try {
buf = pool.borrowObject();
for (int c = in.read(); c != -1; c = in.read()) {
buf.append((char) c);
}
return buf.toString();
} catch (IOException e) {
throw e;
} catch (Exception e) {
throw new RuntimeException("Unable to borrow buffer from pool" + e.toString());
} finally {
try {
in.close();
} catch (Exception e) {
// ignored
}
try {
if (null != buf) {
pool.returnObject(buf);
}
} catch (Exception e) {
// ignored
}
}
}
}
</source>
<p>
Since we've constrained ourselves to the <code>ObjectPool</code> interface, an arbitrary pool
implementation (returning, in our case, <code>StringBuffer</code>s) can be used. When a different
or "better" pool implementation comes along, we can simply drop it into our <code>ReaderUtil</code>
without changing a line of code.
</p>
</section>
<section name="A PooledObjectFactory">
<p>
The implementations provided in pool2 wrap pooled objects in <code>PooledObject</code>
wrappers for internal use by the pool and object factories. The <code>PooledObjectFactory</code>
interface defines lifecycle methods for pooled objects. The simplest way to implement a
<code>PoolableObjectFactory</code> is to extend
<a href="./apidocs/org/apache/commons/pool2/BasePooledObjectFactory.html">
<code>BasePooledObjectFactory</code></a>.
</p>
<p>
Here's a <code>PooledObjectFactory</code> implementation that creates
<code>StringBuffer</code>s as used above.
</p>
<source>
import org.apache.commons.pool3.BasePooledObjectFactory;
import org.apache.commons.pool3.PooledObject;
import org.apache.commons.pool3.impl.DefaultPooledObject;
public class StringBufferFactory
extends BasePooledObjectFactory<StringBuffer> {
@Override
public StringBuffer create() {
return new StringBuffer();
}
/**
* Use the default PooledObject implementation.
*/
@Override
public PooledObject<StringBuffer> wrap(StringBuffer buffer) {
return new DefaultPooledObject<StringBuffer>(buffer);
}
/**
* When an object is returned to the pool, clear the buffer.
*/
@Override
public void passivateObject(PooledObject<StringBuffer> pooledObject) {
pooledObject.getObject().setLength(0);
}
// for all other methods, the no-op implementation
// in BasePooledObjectFactory will suffice
}
</source>
<p>
We can, for example, use this factory with the <code>GenericObjectPool</code> to instantiate our
<code>ReaderUtil</code> as follows:
</p>
<source>ReaderUtil readerUtil = new ReaderUtil(new GenericObjectPool<StringBuffer>(new StringBufferFactory()));</source>
</section>
</body>
</document>