connectionpoolproxydemo.java

thinking in patterns

//: proxy:ConnectionPoolProxyDemo.java
package proxy;
import junit.framework.*;

interface Connection {
  Object get();
  void set(Object x);
  void release();
}

class ConnectionImplementation implements Connection {
  public Object get() { return null; }
  public void set(Object s) {}
  public void release() {} // Never called directly
}

class ConnectionPool { // A singleton
  private static PoolManager pool = new PoolManager();
  private ConnectionPool() {} // Prevent synthesized constructor
  public static void addConnections(int number) {
    for(int i = 0; i < number; i++)
      pool.add(new ConnectionImplementation());
  }
  public static Connection getConnection() {
    PoolManager.ReleasableReference rr = 
      (PoolManager.ReleasableReference)pool.get();
    if(rr == null) return null;
    return new ConnectionProxy(rr);
  }
  // The proxy as a nested class:
  private static 
  class ConnectionProxy implements Connection {
    private PoolManager.ReleasableReference implementation;
    public 
    ConnectionProxy(PoolManager.ReleasableReference rr) {
      implementation = rr;
    }
    public Object get() {
      return 
        ((Connection)implementation.getReference()).get(); 
    }
    public void set(Object x) {
      ((Connection)implementation.getReference()).set(x); 
    }
    public void release() { implementation.release(); }
  }
}

public class ConnectionPoolProxyDemo extends TestCase {
  static {
    ConnectionPool.addConnections(5);
  }
  public void test() {
    Connection c = ConnectionPool.getConnection();
    c.set(new Object());
    c.get();
    c.release();
  }
  public void testDisable() {
    Connection c = ConnectionPool.getConnection();
    String s = null;
    c.set(new Object());
    c.get();
    c.release();
    try {
      c.get();
    } catch(Exception e) {
      s = e.getMessage();
      System.out.println(s);
    }
    assertEquals(s, 
      "Tried to use reference after it was released");
  }
  public static void main(String args[]) {
    junit.textui.TestRunner.run(
      ConnectionPoolProxyDemo.class);
  }
} ///:~