thoerup/circuitbreaker/CircuitBreaker.java

package dk.thoerup.circuitbreaker;


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

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