thoerup/circuitbreaker/CircuitBreaker.java

package dk.thoerup.curcuitbreaker;

import java.util.logging.Logger;

/* 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 (Throwable e) {
                        logger.warning( e.getMessage() );
                        response.sendError(500);
                        return;
                }
                
        }
 */


public class CircuitBreaker{
        Logger logger = Logger.getLogger(CircuitBreaker.class.getName());

        
        private CircuitBreakerState currentState;
        
        private OpenState open = new OpenState();
        private HalfOpenState halfOpen = new HalfOpenState();
        private ClosedState closed = new ClosedState();
        
        private String name;
        
        public CircuitBreaker(String name, int threshold, long timeoutMS) {
                closed.setThreshold(threshold);
                open.setTimeout(timeoutMS);
                
                this.name = name;
                
                reset();
        }
        
        
    public Object invoke(CircuitInvocation invocation) throws Throwable
    {
        Object result = null;
        try
        {
            getState().preInvoke(this);
            result = invocation.proceed();
            getState().postInvoke(this);
        }
        catch(Throwable t)
        {
            getState().onError(this, t);
            throw t;
        }
        return result;
    }
    
    public void tripBreaker() {
        synchronized(this) {
                open.trip();
                currentState = open;

                
                logger.warning("Circuitbreaker tripBreaker - " + name);
        }
    
    }
    
    public void attemptReset() {
        synchronized(this) {
                currentState = halfOpen;
                
                logger.warning("Circuitbreaker attemptReset - " + name);
        }
    }
    
    public void reset() {
        synchronized(this) {
                currentState = closed;
                
                logger.warning("Circuitbreaker reset - " + name);
        }
    }
    
    private CircuitBreakerState getState() {
        synchronized(this) {
                return currentState;
        }
    }
}
1	torben	393	package dk.thoerup.curcuitbreaker;
2
3			import java.util.logging.Logger;
4
5	torben	394	/* Simple CircuitBreaker implementation - snipped from http://www.jroller.com/kenwdelong/entry/circuit_breaker_in_java
6			*
7			* example of how it can be used
8	torben	395
9			private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
10			protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
11	torben	393	class TestInvocation implements CircuitInvocation {
12			String url;
13			public TestInvocation(String url) {
14			this.url = url;
15			}
16			public Object proceed() throws Exception{
17
18			URL u = new URL(url);
19			URLConnection c = u.openConnection();
20			c.connect();
21			InputStream in = c.getInputStream();
22			in.close();
23
24
25			return "hello";
26			}
27
28			}
29			try {
30			String s = (String) cb.invoke(new TestInvocation("http://rafiki/test"));
31			response.getWriter().print(s);
32			} catch (Throwable e) {
33			logger.warning( e.getMessage() );
34			response.sendError(500);
35			return;
36			}
37
38			}
39			*/
40
41
42			public class CircuitBreaker{
43			Logger logger = Logger.getLogger(CircuitBreaker.class.getName());
44
45
46			private CircuitBreakerState currentState;
47
48			private OpenState open = new OpenState();
49			private HalfOpenState halfOpen = new HalfOpenState();
50			private ClosedState closed = new ClosedState();
51
52			private String name;
53
54			public CircuitBreaker(String name, int threshold, long timeoutMS) {
55			closed.setThreshold(threshold);
56			open.setTimeout(timeoutMS);
57
58			this.name = name;
59
60			reset();
61			}
62
63
64			public Object invoke(CircuitInvocation invocation) throws Throwable
65			{
66			Object result = null;
67			try
68			{
69			getState().preInvoke(this);
70			result = invocation.proceed();
71			getState().postInvoke(this);
72			}
73			catch(Throwable t)
74			{
75			getState().onError(this, t);
76			throw t;
77			}
78			return result;
79			}
80
81			public void tripBreaker() {
82			synchronized(this) {
83	torben	396	open.trip();
84	torben	393	currentState = open;
85	torben	396
86	torben	393
87			logger.warning("Circuitbreaker tripBreaker - " + name);
88			}
89
90			}
91
92			public void attemptReset() {
93			synchronized(this) {
94			currentState = halfOpen;
95
96			logger.warning("Circuitbreaker attemptReset - " + name);
97			}
98			}
99
100			public void reset() {
101			synchronized(this) {
102			currentState = closed;
103
104			logger.warning("Circuitbreaker reset - " + name);
105			}
106			}
107
108			private CircuitBreakerState getState() {
109			synchronized(this) {
110			return currentState;
111			}
112			}
113			}