thoerup/circuitbreaker/CircuitBreaker.java

package dk.thoerup.circuitbreaker;


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

import dk.thoerup.circuitbreaker.config.BreakerConfig;
import dk.thoerup.circuitbreaker.config.StaticConfig;
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();
        
        @Deprecated
        public CircuitBreaker(String name, int threshold, int timeoutMS) {
                this(name, new StaticConfig(threshold, timeoutMS) );
        }
        
        public CircuitBreaker(String name, BreakerConfig config) {
                closed.setThreshold(config);
                open.setTimeout(config);
                
                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.config.BreakerConfig;
8	import dk.thoerup.circuitbreaker.config.StaticConfig;
9	import dk.thoerup.circuitbreaker.notification.NotiferHelper;
10	import dk.thoerup.circuitbreaker.notification.Notifier;
11	import dk.thoerup.circuitbreaker.notification.NullNotifier;
12
13	/* Simple CircuitBreaker implementation - snipped from http://www.jroller.com/kenwdelong/entry/circuit_breaker_in_java
14	*
15	* example of how it can be used
16
17	private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
18	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
19	class TestInvocation implements CircuitInvocation {
20	String url;
21	public TestInvocation(String url) {
22	this.url = url;
23	}
24	public Object proceed() throws Exception{
25
26	URL u = new URL(url);
27	URLConnection c = u.openConnection();
28	c.connect();
29	InputStream in = c.getInputStream();
30	in.close();
31
32
33	return "hello";
34	}
35
36	}
37	try {
38	String s = (String) cb.invoke(new TestInvocation("http://rafiki/test"));
39	response.getWriter().print(s);
40	} catch (Exception e) {
41	logger.warning( e.getMessage() );
42	response.sendError(500);
43	return;
44	}
45
46	}
47	*/
48
49
50	public class CircuitBreaker{
51
52	private volatile CircuitBreakerState currentState;
53
54	private final OpenState open = new OpenState();
55	private final HalfOpenState halfOpen = new HalfOpenState();
56	private final ClosedState closed = new ClosedState();
57
58	private String name;
59
60	private ExecutorService executor = null;
61	private Notifier notifier = new NullNotifier();
62
63	@Deprecated
64	public CircuitBreaker(String name, int threshold, int timeoutMS) {
65	this(name, new StaticConfig(threshold, timeoutMS) );
66	}
67
68	public CircuitBreaker(String name, BreakerConfig config) {
69	closed.setThreshold(config);
70	open.setTimeout(config);
71
72	this.name = name;
73
74	//set correct intial state
75	internalReset();
76	}
77
78	public synchronized void shutdown() {
79	if (executor != null) {
80	executor.shutdown();
81	}
82	}
83
84
85	public Object invoke(CircuitInvocation invocation) throws Exception
86	{
87	Object result = null;
88	try
89	{
90	getState().preInvoke(this);
91	result = invocation.proceed();
92	getState().postInvoke(this);
93	}
94	catch(Exception e)
95	{
96	getState().onError(this, e);
97	throw e;
98	}
99	return result;
100	}
101
102	public void tripBreaker() {
103	commonTripBreaker(Notifier.Event.BreakerTripped);
104	}
105
106	//a re-trip should basically do the same as a normal trip, but it is here just to differentiate the two different events
107	public void retripBreaker() {
108	commonTripBreaker(Notifier.Event.BreakerRetripped);
109	}
110
111	private void commonTripBreaker(Notifier.Event event) {
112	synchronized(this) {
113	if (currentState != open) { // TODO:Is this conditional necessary ??
114	open.trip();
115	currentState = open;
116
117	notifier.sendNotification(this, event);
118	}
119	}
120	}
121
122	public void attemptReset() {
123	synchronized(this) {
124	if (currentState != halfOpen) { // TODO:Is this conditional necessary ??
125	currentState = halfOpen;
126	notifier.sendNotification(this, Notifier.Event.BreakerAttemptReset);
127	}
128	}
129
130	}
131
132	public void reset() {
133	synchronized(this) {
134	if (currentState != closed) { // TODO: Is this conditional necessary ??
135	internalReset();
136	notifier.sendNotification(this, Notifier.Event.BreakerReset);
137	}
138	}
139	}
140
141	//This one actually sets the correct closed/reset state
142	private void internalReset() {
143	closed.resetFailureCount();
144	currentState = closed;
145	}
146
147
148	private CircuitBreakerState getState() {
149	synchronized(this) {
150	return currentState;
151	}
152	}
153
154	public boolean isClosed() {
155	return (getState() == closed);
156	}
157
158	public boolean isOpen() {
159	return (getState() == open);
160	}
161
162	public String getName() {
163	return name;
164	}
165
166	public String getStateName() {
167	return getState().getName();
168	}
169
170	public int getThreshold() {
171	return closed.getThreshold();
172	}
173
174	public int getTimeout() {
175	return (int)open.getTimeout();
176	}
177
178	public int getFailureCount() {
179	if (getState() == closed) {
180	return closed.getFailureCount();
181	} else {
182	return -1;
183	}
184	}
185
186	public long getElapsed() {
187	if (getState() == open) {
188	return open.getElapsed();
189	} else {
190	return -1;
191	}
192	}
193
194	public void setNotifier(Notifier notifier) {
195	this.notifier = notifier;
196	}
197
198	public String getNotifierName() {
199	return NotiferHelper.getName(notifier);
200	}
201
202	public synchronized ExecutorService getExecutor() {
203
204	if (executor == null) {
205	executor = Executors.newFixedThreadPool(1);
206	}
207
208	return executor;
209
210	}
211
212	}