thoerup/circuitbreaker/CircuitBreaker.java

package dk.thoerup.curcuitbreaker;


import dk.thoerup.curcuitbreaker.notification.Notifier;
import dk.thoerup.curcuitbreaker.notification.NullNotifier;

/* Simple CircuitBreaker implementation - snipped from http://www.jroller.com/kenwdelong/entry/circuit_breaker_in_java
 * 
 *  example of how it can be used

 private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
                class TestInvocation implements CircuitInvocation {
                        String url;
                        public TestInvocation(String url) {
                                this.url = url;
                        }
                        public Object proceed() throws Exception{
                                
                                URL u = new URL(url);
                                URLConnection c = u.openConnection();
                                c.connect();
                                InputStream in = c.getInputStream();
                                in.close();
                                                        
                                
                                return "hello";
                        }
                        
                }
                try {
                        String s = (String) cb.invoke(new TestInvocation("http://rafiki/test"));
                        response.getWriter().print(s);
                } catch (Exception e) {
                        logger.warning( e.getMessage() );
                        response.sendError(500);
                        return;
                }
                
        }
 */


public class CircuitBreaker{
        
        private volatile CircuitBreakerState currentState;
        
        private final OpenState open = new OpenState();
        private final HalfOpenState halfOpen = new HalfOpenState();
        private final ClosedState closed = new ClosedState();
        
        private String name;
        
        private Notifier notifier = new NullNotifier();
        
        public CircuitBreaker(String name, int threshold, long timeoutMS) {
                closed.setThreshold(threshold);
                open.setTimeout(timeoutMS);
                
                this.name = name;
                
                reset();
        }
        
        
    public Object invoke(CircuitInvocation invocation) throws Exception
    {
        Object result = null;
        try
        {
            getState().preInvoke(this);
            result = invocation.proceed();
            getState().postInvoke(this);
        }
        catch(Exception e)
        {
            getState().onError(this, e);
            throw e;
        }
        return result;
    }
    
    public void tripBreaker() {
        synchronized(this) {
                if (currentState != open) { // TODO:Is this conditional necessary ??
                        open.trip();
                        currentState = open;
                
                        notifier.sendNotification(name, Notifier.Event.BreakerTripped);
                }
        }    
    }
    
    public void attemptReset() {
        synchronized(this) {
                if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
                        currentState = halfOpen;
                        notifier.sendNotification(name, Notifier.Event.BreakerAttemptReset);
                }
        }
        
    }
    
    public void reset() {
        synchronized(this) {
                if (currentState != closed) { // TODO: Is this conditional necessary ??
                        closed.resetFailureCount();
                        currentState = closed;
                        notifier.sendNotification(name, Notifier.Event.BreakerReset);
                }
        }
    }
    
    
    private CircuitBreakerState getState() {
        synchronized(this) {
                return currentState;
        }
    }
    
    public boolean isClosed() {
        return (getState() == closed); 
    }
    
    public boolean isOpen() {
        return (getState() == open); 
    }
    
    public String getName() {
        return name;
    }
    
    public String getStateName() {
        return getState().getName();
    }
    
    public int getThreshold() {
        return closed.getThreshold();
    }
    
    public int getTimeout() {
        return (int)open.getTimeout();
    }
    
    public int getFailureCount() {
        if (getState() == closed) {
                return closed.getFailureCount();
        } else {
                return -1;
        }
    }
    
    public long getElapsed() {
        if (getState() == open) {
                return open.getElapsed();
        } else {
                return -1;
        }
    }
    
    public void setNotifier(Notifier notifier) {
        this.notifier = notifier;
    }
    
    public String getNotifierName() {
        return notifier.getClass().getName();
    }
 
}
1	torben	393	package dk.thoerup.curcuitbreaker;
2
3
4	torben	409	import dk.thoerup.curcuitbreaker.notification.Notifier;
5			import dk.thoerup.curcuitbreaker.notification.NullNotifier;
6
7	torben	394	/* Simple CircuitBreaker implementation - snipped from http://www.jroller.com/kenwdelong/entry/circuit_breaker_in_java
8			*
9			* example of how it can be used
10	torben	395
11			private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
12			protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
13	torben	393	class TestInvocation implements CircuitInvocation {
14			String url;
15			public TestInvocation(String url) {
16			this.url = url;
17			}
18			public Object proceed() throws Exception{
19
20			URL u = new URL(url);
21			URLConnection c = u.openConnection();
22			c.connect();
23			InputStream in = c.getInputStream();
24			in.close();
25
26
27			return "hello";
28			}
29
30			}
31			try {
32			String s = (String) cb.invoke(new TestInvocation("http://rafiki/test"));
33			response.getWriter().print(s);
34	torben	452	} catch (Exception e) {
35	torben	393	logger.warning( e.getMessage() );
36			response.sendError(500);
37			return;
38			}
39
40			}
41			*/
42
43
44			public class CircuitBreaker{
45
46	torben	443	private volatile CircuitBreakerState currentState;
47	torben	393
48	torben	424	private final OpenState open = new OpenState();
49			private final HalfOpenState halfOpen = new HalfOpenState();
50			private final ClosedState closed = new ClosedState();
51	torben	393
52			private String name;
53
54	torben	409	private Notifier notifier = new NullNotifier();
55
56	torben	393	public CircuitBreaker(String name, int threshold, long timeoutMS) {
57			closed.setThreshold(threshold);
58			open.setTimeout(timeoutMS);
59
60			this.name = name;
61
62			reset();
63			}
64
65
66	torben	450	public Object invoke(CircuitInvocation invocation) throws Exception
67	torben	393	{
68			Object result = null;
69			try
70			{
71			getState().preInvoke(this);
72			result = invocation.proceed();
73			getState().postInvoke(this);
74			}
75	torben	450	catch(Exception e)
76	torben	393	{
77	torben	450	getState().onError(this, e);
78			throw e;
79	torben	393	}
80			return result;
81			}
82
83			public void tripBreaker() {
84			synchronized(this) {
85	torben	426	if (currentState != open) { // TODO:Is this conditional necessary ??
86			open.trip();
87			currentState = open;
88	torben	393
89	torben	426	notifier.sendNotification(name, Notifier.Event.BreakerTripped);
90			}
91	torben	409	}
92	torben	393	}
93
94			public void attemptReset() {
95			synchronized(this) {
96	torben	426	if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
97			currentState = halfOpen;
98			notifier.sendNotification(name, Notifier.Event.BreakerAttemptReset);
99			}
100	torben	393	}
101	torben	409
102	torben	393	}
103
104			public void reset() {
105			synchronized(this) {
106	torben	426	if (currentState != closed) { // TODO: Is this conditional necessary ??
107	torben	456	closed.resetFailureCount();
108	torben	426	currentState = closed;
109			notifier.sendNotification(name, Notifier.Event.BreakerReset);
110			}
111	torben	393	}
112			}
113
114	torben	397
115	torben	393	private CircuitBreakerState getState() {
116			synchronized(this) {
117			return currentState;
118			}
119			}
120	torben	397
121	torben	447	public boolean isClosed() {
122			return (getState() == closed);
123			}
124
125			public boolean isOpen() {
126			return (getState() == open);
127			}
128
129	torben	397	public String getName() {
130			return name;
131			}
132
133			public String getStateName() {
134			return getState().getName();
135			}
136
137			public int getThreshold() {
138			return closed.getThreshold();
139			}
140
141	torben	413	public int getTimeout() {
142			return (int)open.getTimeout();
143			}
144
145	torben	397	public int getFailureCount() {
146			if (getState() == closed) {
147			return closed.getFailureCount();
148			} else {
149			return -1;
150			}
151			}
152
153			public long getElapsed() {
154			if (getState() == open) {
155			return open.getElapsed();
156			} else {
157			return -1;
158			}
159			}
160	torben	409
161			public void setNotifier(Notifier notifier) {
162			this.notifier = notifier;
163			}
164
165			public String getNotifierName() {
166	torben	412	return notifier.getClass().getName();
167	torben	409	}
168	torben	397
169	torben	393	}