thoerup/circuitbreaker/CircuitBreaker.java

package dk.thoerup.circuitbreaker;


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 Notifier notifier = new NullNotifier();
        
        public CircuitBreaker(String name, int threshold, long timeoutMS) {
                closed.setThreshold(threshold);
                open.setTimeout(timeoutMS);
                
                this.name = name;
        
                // Initial state is open - like a reset() was called initially
                closed.resetFailureCount();
                currentState = closed;
        }
        
        
    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	package dk.thoerup.circuitbreaker;
2
3
4	import dk.thoerup.circuitbreaker.notification.Notifier;
5	import dk.thoerup.circuitbreaker.notification.NullNotifier;
6
7	/* 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
11	private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
12	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
13	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	} catch (Exception e) {
35	logger.warning( e.getMessage() );
36	response.sendError(500);
37	return;
38	}
39
40	}
41	*/
42
43
44	public class CircuitBreaker{
45
46	private volatile CircuitBreakerState currentState;
47
48	private final OpenState open = new OpenState();
49	private final HalfOpenState halfOpen = new HalfOpenState();
50	private final ClosedState closed = new ClosedState();
51
52	private String name;
53
54	private Notifier notifier = new NullNotifier();
55
56	public CircuitBreaker(String name, int threshold, long timeoutMS) {
57	closed.setThreshold(threshold);
58	open.setTimeout(timeoutMS);
59
60	this.name = name;
61
62	// Initial state is open - like a reset() was called initially
63	closed.resetFailureCount();
64	currentState = closed;
65	}
66
67
68	public Object invoke(CircuitInvocation invocation) throws Exception
69	{
70	Object result = null;
71	try
72	{
73	getState().preInvoke(this);
74	result = invocation.proceed();
75	getState().postInvoke(this);
76	}
77	catch(Exception e)
78	{
79	getState().onError(this, e);
80	throw e;
81	}
82	return result;
83	}
84
85	public void tripBreaker() {
86	synchronized(this) {
87	if (currentState != open) { // TODO:Is this conditional necessary ??
88	open.trip();
89	currentState = open;
90
91	notifier.sendNotification(name, Notifier.Event.BreakerTripped);
92	}
93	}
94	}
95
96	public void attemptReset() {
97	synchronized(this) {
98	if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
99	currentState = halfOpen;
100	notifier.sendNotification(name, Notifier.Event.BreakerAttemptReset);
101	}
102	}
103
104	}
105
106	public void reset() {
107	synchronized(this) {
108	if (currentState != closed) { // TODO: Is this conditional necessary ??
109	closed.resetFailureCount();
110	currentState = closed;
111	notifier.sendNotification(name, Notifier.Event.BreakerReset);
112	}
113	}
114	}
115
116
117	private CircuitBreakerState getState() {
118	synchronized(this) {
119	return currentState;
120	}
121	}
122
123	public boolean isClosed() {
124	return (getState() == closed);
125	}
126
127	public boolean isOpen() {
128	return (getState() == open);
129	}
130
131	public String getName() {
132	return name;
133	}
134
135	public String getStateName() {
136	return getState().getName();
137	}
138
139	public int getThreshold() {
140	return closed.getThreshold();
141	}
142
143	public int getTimeout() {
144	return (int)open.getTimeout();
145	}
146
147	public int getFailureCount() {
148	if (getState() == closed) {
149	return closed.getFailureCount();
150	} else {
151	return -1;
152	}
153	}
154
155	public long getElapsed() {
156	if (getState() == open) {
157	return open.getElapsed();
158	} else {
159	return -1;
160	}
161	}
162
163	public void setNotifier(Notifier notifier) {
164	this.notifier = notifier;
165	}
166
167	public String getNotifierName() {
168	return notifier.getClass().getName();
169	}
170
171	}