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;
        
                //set correct intial state
                internalReset();
        }
        
        
    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 ??
                        internalReset();
                        notifier.sendNotification(name, 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();
    }
 
}
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	//set correct intial state
63	internalReset();
64	}
65
66
67	public Object invoke(CircuitInvocation invocation) throws Exception
68	{
69	Object result = null;
70	try
71	{
72	getState().preInvoke(this);
73	result = invocation.proceed();
74	getState().postInvoke(this);
75	}
76	catch(Exception e)
77	{
78	getState().onError(this, e);
79	throw e;
80	}
81	return result;
82	}
83
84	public void tripBreaker() {
85	synchronized(this) {
86	if (currentState != open) { // TODO:Is this conditional necessary ??
87	open.trip();
88	currentState = open;
89
90	notifier.sendNotification(name, Notifier.Event.BreakerTripped);
91	}
92	}
93	}
94
95	public void attemptReset() {
96	synchronized(this) {
97	if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
98	currentState = halfOpen;
99	notifier.sendNotification(name, Notifier.Event.BreakerAttemptReset);
100	}
101	}
102
103	}
104
105	public void reset() {
106	synchronized(this) {
107	if (currentState != closed) { // TODO: Is this conditional necessary ??
108	internalReset();
109	notifier.sendNotification(name, Notifier.Event.BreakerReset);
110	}
111	}
112	}
113
114	//This one actually sets the correct closed/reset state
115	private void internalReset() {
116	closed.resetFailureCount();
117	currentState = closed;
118	}
119
120
121	private CircuitBreakerState getState() {
122	synchronized(this) {
123	return currentState;
124	}
125	}
126
127	public boolean isClosed() {
128	return (getState() == closed);
129	}
130
131	public boolean isOpen() {
132	return (getState() == open);
133	}
134
135	public String getName() {
136	return name;
137	}
138
139	public String getStateName() {
140	return getState().getName();
141	}
142
143	public int getThreshold() {
144	return closed.getThreshold();
145	}
146
147	public int getTimeout() {
148	return (int)open.getTimeout();
149	}
150
151	public int getFailureCount() {
152	if (getState() == closed) {
153	return closed.getFailureCount();
154	} else {
155	return -1;
156	}
157	}
158
159	public long getElapsed() {
160	if (getState() == open) {
161	return open.getElapsed();
162	} else {
163	return -1;
164	}
165	}
166
167	public void setNotifier(Notifier notifier) {
168	this.notifier = notifier;
169	}
170
171	public String getNotifierName() {
172	return notifier.getClass().getName();
173	}
174
175	}