Fix for issue #413: Circuit Breaker Pattern (#986)

* Fix Issue #413: Circuit-Breaker Pattern

* Fix Image Links

* Remove Javadoc plugin to ensure correct build

* Implementing code review feedback

* Sync README with actual code

circuit-breaker/src/main/java/com/iluwatar/circuitbreaker/App.java

@@ -0,0 +1,86 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.circuitbreaker;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * <p>
+ * The intention of the Circuit Builder pattern is to handle remote failures 
+ * robustly, which is to mean that if a service is dependant on n number of
+ * other services, and m of them fail, we should be able to recover from that
+ * failure by ensuring that the user can still use the services that are actually
+ * functional, and resources are not tied up by uselessly by the services which
+ * are not working. However, we should also be able to detect when any of the m
+ * failing services become operational again, so that we can use it
+ * </p>
+ * <p>
+ * In this example, the circuit breaker pattern is demonstrated by using two services:
+ * {@link MonitoringService} and {@link DelayedService}. The monitoring service
+ * is responsible for calling two services: a local service and a remote service {@link DelayedService}
+ * , and by using the circuit breaker construction we ensure that if the call to
+ * remote service is going to fail, we are going to save our resources and not make the 
+ * function call at all, by wrapping our call to the remote service in the circuit
+ * breaker object.
+ * </p>
+ * <p>
+ * This works as follows: The {@link CircuitBreaker} object can be in one of three
+ * states: <b>Open</b>, <b>Closed</b> and <b>Half-Open</b>, which represents the real
+ * world circuits. If the state is closed (initial), we assume everything is alright
+ * and perform the function call. However, every time the call fails, we note it
+ * and once it crosses a threshold, we set the state to Open, preventing any further
+ * calls to the remote server. Then, after a certain retry period (during which we
+ * expect thee service to recover), we make another call to the remote server and
+ * this state is called the Half-Open state, where it stays till the service is down,
+ * and once it recovers, it goes back to the closed state and the cycle continues.
+ * </p>
+ */
+public class App {
+   
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+    
+   /**
+   * Program entry point
+   * 
+   * @param args command line args
+   */
+  public static void main(String[] args) {
+    //Create an object of monitoring service which makes both local and remote calls
+    var obj = new MonitoringService();
+    //Set the circuit Breaker parameters
+    var circuitBreaker = new CircuitBreaker(3000, 1, 2000 * 1000 * 1000); 
+    var serverStartTime = System.nanoTime();
+    while (true) {
+      LOGGER.info(obj.localResourceResponse());
+      LOGGER.info(obj.remoteResourceResponse(circuitBreaker, serverStartTime));
+      LOGGER.info(circuitBreaker.getState());
+      try {
+        Thread.sleep(5 * 1000); 
+      } catch (InterruptedException e) {
+        LOGGER.error(e.getMessage());
+      }
+    }
+  }
+}