src/site/xdoc/examples.xml - commons-pool - Git at Google

 <?xml version="1.0"?>
 <!--
    Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

        https://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
 -->
 <document xmlns="http://maven.apache.org/XDOC/2.0"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">
    <properties>
       <title>Examples</title>
       <author email="dev@commons.apache.org">Apache Commons Documentation Team</author>
    </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&lt;StringBuffer&gt; pool;

     public ReaderUtil(ObjectPool&lt;StringBuffer&gt; 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&lt;StringBuffer&gt; {

     @Override
     public StringBuffer create() {
         return new StringBuffer();
     }

     /**
      * Use the default PooledObject implementation.
      */
     @Override
     public PooledObject&lt;StringBuffer&gt; wrap(StringBuffer buffer) {
         return new DefaultPooledObject&lt;StringBuffer&gt;(buffer);
     }

     /**
      * When an object is returned to the pool, clear the buffer.
      */
     @Override
     public void passivateObject(PooledObject&lt;StringBuffer&gt; 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&lt;StringBuffer&gt;(new StringBufferFactory()));</source>
       </section>
    </body>
 </document>
	<?xml version="1.0"?>
	<!--
	Licensed to the Apache Software Foundation (ASF) under one or more
	contributor license agreements. See the NOTICE file distributed with
	this work for additional information regarding copyright ownership.
	The ASF licenses this file to You under the Apache License, Version 2.0
	(the "License"); you may not use this file except in compliance with
	the License. You may obtain a copy of the License at

	https://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	-->
	<document xmlns="http://maven.apache.org/XDOC/2.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">
	<properties>
	<title>Examples</title>
	<author email="dev@commons.apache.org">Apache Commons Documentation Team</author>
	</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>