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	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.NotiferHelper;
8	import dk.thoerup.circuitbreaker.notification.Notifier;
9	import dk.thoerup.circuitbreaker.notification.NullNotifier;
10
11	/* 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
15	private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
16	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
17	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	} catch (Exception e) {
39	logger.warning( e.getMessage() );
40	response.sendError(500);
41	return;
42	}
43
44	}
45	*/
46
47
48	public class CircuitBreaker{
49
50	private volatile CircuitBreakerState currentState;
51
52	private final OpenState open = new OpenState();
53	private final HalfOpenState halfOpen = new HalfOpenState();
54	private final ClosedState closed = new ClosedState();
55
56	private String name;
57
58	private ExecutorService executor = null;
59	private Notifier notifier = new NullNotifier();
60
61	public CircuitBreaker(String name, int threshold, long timeoutMS) {
62	closed.setThreshold(threshold);
63	open.setTimeout(timeoutMS);
64
65	this.name = name;
66
67	//set correct intial state
68	internalReset();
69	}
70
71	public synchronized void shutdown() {
72	if (executor != null) {
73	executor.shutdown();
74	}
75	}
76
77
78	public Object invoke(CircuitInvocation invocation) throws Exception
79	{
80	Object result = null;
81	try
82	{
83	getState().preInvoke(this);
84	result = invocation.proceed();
85	getState().postInvoke(this);
86	}
87	catch(Exception e)
88	{
89	getState().onError(this, e);
90	throw e;
91	}
92	return result;
93	}
94
95	public void tripBreaker() {
96	commonTripBreaker(Notifier.Event.BreakerTripped);
97	}
98
99	//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	commonTripBreaker(Notifier.Event.BreakerRetripped);
102	}
103
104	private void commonTripBreaker(Notifier.Event event) {
105	synchronized(this) {
106	if (currentState != open) { // TODO:Is this conditional necessary ??
107	open.trip();
108	currentState = open;
109
110	notifier.sendNotification(this, event);
111	}
112	}
113	}
114
115	public void attemptReset() {
116	synchronized(this) {
117	if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
118	currentState = halfOpen;
119	notifier.sendNotification(this, Notifier.Event.BreakerAttemptReset);
120	}
121	}
122
123	}
124
125	public void reset() {
126	synchronized(this) {
127	if (currentState != closed) { // TODO: Is this conditional necessary ??
128	internalReset();
129	notifier.sendNotification(this, Notifier.Event.BreakerReset);
130	}
131	}
132	}
133
134	//This one actually sets the correct closed/reset state
135	private void internalReset() {
136	closed.resetFailureCount();
137	currentState = closed;
138	}
139
140
141	private CircuitBreakerState getState() {
142	synchronized(this) {
143	return currentState;
144	}
145	}
146
147	public boolean isClosed() {
148	return (getState() == closed);
149	}
150
151	public boolean isOpen() {
152	return (getState() == open);
153	}
154
155	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	public int getTimeout() {
168	return (int)open.getTimeout();
169	}
170
171	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
187	public void setNotifier(Notifier notifier) {
188	this.notifier = notifier;
189	}
190
191	public String getNotifierName() {
192	return NotiferHelper.getName(notifier);
193	}
194
195	public synchronized ExecutorService getExecutor() {
196
197	if (executor == null) {
198	executor = Executors.newFixedThreadPool(1);
199	}
200
201	return executor;
202
203	}
204
205	}