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<document>
   <properties>
      <title>Examples</title>
      <author email="dev@commons.apache.org">Commons Documentation Team</author>
      <author email="rwaldhoff@apache.org">Rodney Waldhoff</author>
      <revision>$Id: examples.xml 1221705 2011-12-21 13:03:54Z ggregory $</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 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 org.apache.commons.pool.ObjectPool;
import java.io.Reader; 
import java.io.IOException; 
 
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 implemenatation comes along, we can simply drop it into our <code>ReaderUtil</code>
       without changing a line of code.  
      </p>
      </section>
      <section name="A PoolableObjectFactory">
       <p>
        Recall that Pool provides a simple toolkit for creating object pools.  The 
        <code>PoolableObjectFactory</code> interface is an important part of this toolkit.
        <code>PoolableObjectFactory</code> defines lifecycle methods for pooled objects. 
        We can use it to separate the kinds of objects that are pooled and how they are 
        created, persisted, or destroyed, from the pooling algorithm itself.
       </p>
       <p>
        Suppose we have an <code>ObjectPool</code> implementation that accepts a 
        <code>PoolableObjectFactory</code> (for example, any of the implementations in the
        <code>org.apache.commons.pool.impl</code> package).  Then we need only provide 
        the factory implemenation in order to pool a new kind of object.  
       </p>
       <p>
        Here's a <code>PoolableObjectFactory</code> implementation that creates
        <code>StringBuffer</code>s as used above.
       </p>
<source>
import org.apache.commons.pool.BasePoolableObjectFactory; 
 
public class StringBufferFactory extends BasePoolableObjectFactory&lt;StringBuffer&gt; { 
    // for makeObject we'll simply return a new buffer 
    public StringBuffer makeObject() { 
        return new StringBuffer(); 
    } 
     
    // when an object is returned to the pool,  
    // we'll clear it out 
    public void passivateObject(StringBuffer buf) { 
        buf.setLength(0); 
    } 
     
    // for all other methods, the no-op  
    // implementation in BasePoolableObjectFactory 
    // will suffice 
}
</source>
      <p>
       We can, for example, use this factory with the <code>StackObjectPool</code> to instantiate our
       <code>ReaderUtil</code> as follows:
      </p>
<source>new ReaderUtil(new StackObjectPool&lt;StringBuffer&gt;(new StringBufferFactory()))</source>
      </section>
   </body>
</document>
