thoerup/circuitbreaker/CircuitBreaker.java

package dk.thoerup.circuitbreaker;


import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import dk.thoerup.circuitbreaker.notification.NotiferHelper;
import dk.thoerup.circuitbreaker.notification.Notifier;
import dk.thoerup.circuitbreaker.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 ExecutorService executor = null;        
        private Notifier notifier = new NullNotifier();
        
        public CircuitBreaker(String name, int threshold, long timeoutMS) {
                closed.setThreshold(threshold);
                open.setTimeout(timeoutMS);
                
                this.name = name;
        
                //set correct intial state
                internalReset();
        }
        
        public synchronized void shutdown() {
                if (executor != null) {
                        executor.shutdown();
                }
        }
        
        
    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() {
        commonTripBreaker(Notifier.Event.BreakerTripped);
    }
    
        //a re-trip should basically do the same as a normal trip, but it is here just to differentiate the two different events
    public void retripBreaker() {
        commonTripBreaker(Notifier.Event.BreakerRetripped);
    }
    
    private void commonTripBreaker(Notifier.Event event) {
        synchronized(this) {
                if (currentState != open) { // TODO:Is this conditional necessary ??
                        open.trip();
                        currentState = open;
                
                        notifier.sendNotification(this, event);
                }
        }       
    }

    public void attemptReset() {
        synchronized(this) {
                if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
                        currentState = halfOpen;
                        notifier.sendNotification(this, Notifier.Event.BreakerAttemptReset);
                }
        }
        
    }
    
    public void reset() {
        synchronized(this) {
                if (currentState != closed) { // TODO: Is this conditional necessary ??
                        internalReset();
                        notifier.sendNotification(this, Notifier.Event.BreakerReset);
                }
        }
    }
    
    //This one actually sets the correct closed/reset state 
    private void internalReset() {
                closed.resetFailureCount();
                currentState = closed;          
    }
    
    
    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 NotiferHelper.getName(notifier);
    }
    
    public synchronized ExecutorService getExecutor() {
        
        if (executor == null) {
                executor = Executors.newFixedThreadPool(1);
        }
        
        return executor;
        
    }
 
}
1	torben	467	package dk.thoerup.circuitbreaker;
2	torben	393
3
4	torben	1148	import java.util.concurrent.ExecutorService;
5			import java.util.concurrent.Executors;
6
7	torben	1289	import dk.thoerup.circuitbreaker.notification.NotiferHelper;
8	torben	467	import dk.thoerup.circuitbreaker.notification.Notifier;
9			import dk.thoerup.circuitbreaker.notification.NullNotifier;
10	torben	409
11	torben	394	/* Simple CircuitBreaker implementation - snipped from http://www.jroller.com/kenwdelong/entry/circuit_breaker_in_java
12			*
13			* example of how it can be used
14	torben	395
15			private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
16			protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
17	torben	393	class TestInvocation implements CircuitInvocation {
18			String url;
19			public TestInvocation(String url) {
20			this.url = url;
21			}
22			public Object proceed() throws Exception{
23
24			URL u = new URL(url);
25			URLConnection c = u.openConnection();
26			c.connect();
27			InputStream in = c.getInputStream();
28			in.close();
29
30
31			return "hello";
32			}
33
34			}
35			try {
36			String s = (String) cb.invoke(new TestInvocation("http://rafiki/test"));
37			response.getWriter().print(s);
38	torben	452	} catch (Exception e) {
39	torben	393	logger.warning( e.getMessage() );
40			response.sendError(500);
41			return;
42			}
43
44			}
45			*/
46
47
48			public class CircuitBreaker{
49
50	torben	443	private volatile CircuitBreakerState currentState;
51	torben	393
52	torben	424	private final OpenState open = new OpenState();
53			private final HalfOpenState halfOpen = new HalfOpenState();
54			private final ClosedState closed = new ClosedState();
55	torben	393
56			private String name;
57
58	torben	1148	private ExecutorService executor = null;
59	torben	409	private Notifier notifier = new NullNotifier();
60
61	torben	393	public CircuitBreaker(String name, int threshold, long timeoutMS) {
62			closed.setThreshold(threshold);
63			open.setTimeout(timeoutMS);
64
65			this.name = name;
66	torben	625
67	torben	627	//set correct intial state
68			internalReset();
69	torben	393	}
70
71	torben	1148	public synchronized void shutdown() {
72			if (executor != null) {
73			executor.shutdown();
74			}
75			}
76	torben	393
77	torben	1148
78	torben	450	public Object invoke(CircuitInvocation invocation) throws Exception
79	torben	393	{
80			Object result = null;
81			try
82			{
83			getState().preInvoke(this);
84			result = invocation.proceed();
85			getState().postInvoke(this);
86			}
87	torben	450	catch(Exception e)
88	torben	393	{
89	torben	450	getState().onError(this, e);
90			throw e;
91	torben	393	}
92			return result;
93			}
94
95			public void tripBreaker() {
96	torben	871	commonTripBreaker(Notifier.Event.BreakerTripped);
97	torben	393	}
98
99	torben	864	//a re-trip should basically do the same as a normal trip, but it is here just to differentiate the two different events
100			public void retripBreaker() {
101	torben	871	commonTripBreaker(Notifier.Event.BreakerRetripped);
102			}
103
104			private void commonTripBreaker(Notifier.Event event) {
105			synchronized(this) {
106	torben	864	if (currentState != open) { // TODO:Is this conditional necessary ??
107			open.trip();
108			currentState = open;
109
110	torben	1161	notifier.sendNotification(this, event);
111	torben	864	}
112	torben	871	}
113	torben	864	}
114
115	torben	393	public void attemptReset() {
116			synchronized(this) {
117	torben	426	if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
118			currentState = halfOpen;
119	torben	1161	notifier.sendNotification(this, Notifier.Event.BreakerAttemptReset);
120	torben	426	}
121	torben	393	}
122	torben	409
123	torben	393	}
124
125			public void reset() {
126			synchronized(this) {
127	torben	426	if (currentState != closed) { // TODO: Is this conditional necessary ??
128	torben	627	internalReset();
129	torben	1161	notifier.sendNotification(this, Notifier.Event.BreakerReset);
130	torben	426	}
131	torben	393	}
132			}
133
134	torben	627	//This one actually sets the correct closed/reset state
135			private void internalReset() {
136			closed.resetFailureCount();
137			currentState = closed;
138			}
139	torben	397
140	torben	627
141	torben	393	private CircuitBreakerState getState() {
142			synchronized(this) {
143			return currentState;
144			}
145			}
146	torben	397
147	torben	447	public boolean isClosed() {
148			return (getState() == closed);
149			}
150
151			public boolean isOpen() {
152			return (getState() == open);
153			}
154
155	torben	397	public String getName() {
156			return name;
157			}
158
159			public String getStateName() {
160			return getState().getName();
161			}
162
163			public int getThreshold() {
164			return closed.getThreshold();
165			}
166
167	torben	413	public int getTimeout() {
168			return (int)open.getTimeout();
169			}
170
171	torben	397	public int getFailureCount() {
172			if (getState() == closed) {
173			return closed.getFailureCount();
174			} else {
175			return -1;
176			}
177			}
178
179			public long getElapsed() {
180			if (getState() == open) {
181			return open.getElapsed();
182			} else {
183			return -1;
184			}
185			}
186	torben	409
187			public void setNotifier(Notifier notifier) {
188			this.notifier = notifier;
189			}
190
191	torben	1289	public String getNotifierName() {
192			return NotiferHelper.getName(notifier);
193	torben	409	}
194	torben	1148
195			public synchronized ExecutorService getExecutor() {
196
197			if (executor == null) {
198			executor = Executors.newFixedThreadPool(1);
199			}
200
201			return executor;
202
203			}
204	torben	397
205	torben	393	}