1 |
torben |
467 |
package dk.thoerup.circuitbreaker; |
2 |
torben |
393 |
|
3 |
|
|
|
4 |
torben |
467 |
import dk.thoerup.circuitbreaker.notification.Notifier; |
5 |
|
|
import dk.thoerup.circuitbreaker.notification.NullNotifier; |
6 |
torben |
409 |
|
7 |
torben |
394 |
/* 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 |
torben |
395 |
|
11 |
|
|
private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000); |
12 |
|
|
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { |
13 |
torben |
393 |
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 |
torben |
452 |
} catch (Exception e) { |
35 |
torben |
393 |
logger.warning( e.getMessage() ); |
36 |
|
|
response.sendError(500); |
37 |
|
|
return; |
38 |
|
|
} |
39 |
|
|
|
40 |
|
|
} |
41 |
|
|
*/ |
42 |
|
|
|
43 |
|
|
|
44 |
|
|
public class CircuitBreaker{ |
45 |
|
|
|
46 |
torben |
443 |
private volatile CircuitBreakerState currentState; |
47 |
torben |
393 |
|
48 |
torben |
424 |
private final OpenState open = new OpenState(); |
49 |
|
|
private final HalfOpenState halfOpen = new HalfOpenState(); |
50 |
|
|
private final ClosedState closed = new ClosedState(); |
51 |
torben |
393 |
|
52 |
|
|
private String name; |
53 |
|
|
|
54 |
torben |
409 |
private Notifier notifier = new NullNotifier(); |
55 |
|
|
|
56 |
torben |
393 |
public CircuitBreaker(String name, int threshold, long timeoutMS) { |
57 |
|
|
closed.setThreshold(threshold); |
58 |
|
|
open.setTimeout(timeoutMS); |
59 |
|
|
|
60 |
|
|
this.name = name; |
61 |
torben |
625 |
|
62 |
torben |
626 |
// Initial state is closed - like a reset() was called initially |
63 |
torben |
625 |
closed.resetFailureCount(); |
64 |
|
|
currentState = closed; |
65 |
torben |
393 |
} |
66 |
|
|
|
67 |
|
|
|
68 |
torben |
450 |
public Object invoke(CircuitInvocation invocation) throws Exception |
69 |
torben |
393 |
{ |
70 |
|
|
Object result = null; |
71 |
|
|
try |
72 |
|
|
{ |
73 |
|
|
getState().preInvoke(this); |
74 |
|
|
result = invocation.proceed(); |
75 |
|
|
getState().postInvoke(this); |
76 |
|
|
} |
77 |
torben |
450 |
catch(Exception e) |
78 |
torben |
393 |
{ |
79 |
torben |
450 |
getState().onError(this, e); |
80 |
|
|
throw e; |
81 |
torben |
393 |
} |
82 |
|
|
return result; |
83 |
|
|
} |
84 |
|
|
|
85 |
|
|
public void tripBreaker() { |
86 |
|
|
synchronized(this) { |
87 |
torben |
426 |
if (currentState != open) { // TODO:Is this conditional necessary ?? |
88 |
|
|
open.trip(); |
89 |
|
|
currentState = open; |
90 |
torben |
393 |
|
91 |
torben |
426 |
notifier.sendNotification(name, Notifier.Event.BreakerTripped); |
92 |
|
|
} |
93 |
torben |
409 |
} |
94 |
torben |
393 |
} |
95 |
|
|
|
96 |
|
|
public void attemptReset() { |
97 |
|
|
synchronized(this) { |
98 |
torben |
426 |
if (currentState != halfOpen) { // TODO:Is this conditional necessary ?? |
99 |
|
|
currentState = halfOpen; |
100 |
|
|
notifier.sendNotification(name, Notifier.Event.BreakerAttemptReset); |
101 |
|
|
} |
102 |
torben |
393 |
} |
103 |
torben |
409 |
|
104 |
torben |
393 |
} |
105 |
|
|
|
106 |
|
|
public void reset() { |
107 |
|
|
synchronized(this) { |
108 |
torben |
426 |
if (currentState != closed) { // TODO: Is this conditional necessary ?? |
109 |
torben |
456 |
closed.resetFailureCount(); |
110 |
torben |
426 |
currentState = closed; |
111 |
|
|
notifier.sendNotification(name, Notifier.Event.BreakerReset); |
112 |
|
|
} |
113 |
torben |
393 |
} |
114 |
|
|
} |
115 |
|
|
|
116 |
torben |
397 |
|
117 |
torben |
393 |
private CircuitBreakerState getState() { |
118 |
|
|
synchronized(this) { |
119 |
|
|
return currentState; |
120 |
|
|
} |
121 |
|
|
} |
122 |
torben |
397 |
|
123 |
torben |
447 |
public boolean isClosed() { |
124 |
|
|
return (getState() == closed); |
125 |
|
|
} |
126 |
|
|
|
127 |
|
|
public boolean isOpen() { |
128 |
|
|
return (getState() == open); |
129 |
|
|
} |
130 |
|
|
|
131 |
torben |
397 |
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 |
torben |
413 |
public int getTimeout() { |
144 |
|
|
return (int)open.getTimeout(); |
145 |
|
|
} |
146 |
|
|
|
147 |
torben |
397 |
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 |
torben |
409 |
|
163 |
|
|
public void setNotifier(Notifier notifier) { |
164 |
|
|
this.notifier = notifier; |
165 |
|
|
} |
166 |
|
|
|
167 |
|
|
public String getNotifierName() { |
168 |
torben |
412 |
return notifier.getClass().getName(); |
169 |
torben |
409 |
} |
170 |
torben |
397 |
|
171 |
torben |
393 |
} |