Chain of Responsibility in Java
Why read if you can watch?
Watch Chain of Responsibility's video tutorialBefore and after
BEFORE - the client is responsible for stepping through the "list" of Handler objects, and deter- mining when the request has been handled.
class Handler
{
private static java.util.Random s_rn = new java.util.Random();
private static int s_next = 1;
private int m_id = s_next++;
public boolean handle(int num)
{
if (s_rn.nextInt(4) != 0)
{
System.out.print(m_id + "-busy ");
return false;
}
System.out.println(m_id + "-handled-" + num);
return true;
}
}
public class ChainDemo
{
public static void main(String[] args)
{
Handler[] nodes =
{
new Handler(), new Handler(), new Handler(), new Handler()
};
for (int i = 1, j; i < 10; i++)
{
j = 0;
while (!nodes[j].handle(i))
j = (j + 1) % nodes.length;
}
}
}
1-busy 2-busy 3-busy 4-busy 1-busy 2-handled-1
1-busy 2-busy 3-handled-2
1-busy 2-busy 3-busy 4-handled-3
1-busy 2-busy 3-busy 4-busy 1-busy 2-busy
3-handled-4
1-busy 2-busy 3-handled-5
1-handled-6
1-busy 2-handled-7
1-busy 2-busy 3-busy 4-busy 1-busy 2-busy
3-busy 4-handled-8
1-busy 2-handled-9
AFTER - the client submits each request to the "chain" abstraction and is decoupled from all sub- sequent processing.
class Handler
{
private static java.util.Random s_rn = new java.util.Random();
private static int s_next = 1;
private int m_id = s_next++;
private Handler m_next;
public void add(Handler next)
{
if (m_next == null)
m_next = next;
else
m_next.add(next);
}
public void wrap_around(Handler root)
{
if (m_next == null)
m_next = root;
else
m_next.wrap_around(root);
}
public void handle(int num)
{
if (s_rn.nextInt(4) != 0)
{
System.out.print(m_id + "-busy ");
m_next.handle(num);
}
else
System.out.println(m_id + "-handled-" + num);
}
}
public class ChainDemo
{
public static void main(String[] args)
{
Handler chain_root = new Handler();
chain_root.add(new Handler());
chain_root.add(new Handler());
chain_root.add(new Handler());
chain_root.wrap_around(chain);
for (int i = 1; i < 10; i++)
chain_root.handle(i);
}
}
1-busy 2-busy 3-handled-1
1-busy 2-busy 3-busy 4-busy 1-handled-2
1-busy 2-busy 3-busy 4-busy 1-busy 2-busy
3-busy 4-busy 1-handled-3
1-busy 2-handled-4
1-busy 2-busy 3-busy 4-handled-5
1-busy 2-busy 3-busy 4-busy 1-busy 2-handled-6
1-busy 2-handled-7
1-handled-8
1-busy 2-busy 3-handled-9
