#1510 Fix review comments

circuit-breaker/README.md

@@ -19,12 +19,15 @@ cannot bring the whole application down, and we can reconnect to the service as
 
 Real world example
 
-> Imagine a web application that has both local files/images and remote database entries to serve. 
-> The database might not be responding due to a variety of reasons, so if the application keeps 
-> trying to read from the database using multiple threads/processes, soon all of them will hang 
-> causing our entire web application will crash. We should be able to detect this situation and show 
-> the user an appropriate message so that he/she can explore other parts of the app unaffected by 
-> the database failure. 
+> Imagine a web application that has both local files/images and remote services that are used for 
+> fetching data. These remote services may be either healthy and responsive at times, or may become 
+> slow and unresponsive at some point of time due to variety of reasons. So if one of the remote 
+> services is slow or not responding successfully, our application will try to fetch response from 
+> the remote service using multiple threads/processes, soon all of them will hang (also called 
+> [thread starvation](https://en.wikipedia.org/wiki/Starvation_(computer_science))) causing our entire web application to crash. We should be able to detect 
+> this situation and show the user an appropriate message so that he/she can explore other parts of 
+> the app unaffected by the remote service failure. Meanwhile, the other services that are working 
+> normally, should keep functioning unaffected by this failure.
 
 In plain words
 
@@ -65,12 +68,10 @@ public class App {
     var serverStartTime = System.nanoTime();
 
     var delayedService = new DelayedRemoteService(serverStartTime, 5);
-    //Set the circuit Breaker parameters
     var delayedServiceCircuitBreaker = new DefaultCircuitBreaker(delayedService, 3000, 2,
         2000 * 1000 * 1000);
 
     var quickService = new QuickRemoteService();
-    //Set the circuit Breaker parameters
     var quickServiceCircuitBreaker = new DefaultCircuitBreaker(quickService, 3000, 2,
         2000 * 1000 * 1000);
 
@@ -95,6 +96,7 @@ public class App {
 
     //Wait for the delayed service to become responsive
     try {
+      LOGGER.info("Waiting for delayed service to become responsive");
       Thread.sleep(5000);
     } catch (InterruptedException e) {
       e.printStackTrace();
@@ -166,6 +168,7 @@ public class DefaultCircuitBreaker implements CircuitBreaker {
   private final long retryTimePeriod;
   private final RemoteService service;
   long lastFailureTime;
+  private String lastFailureResponse;
   int failureCount;
   private final int failureThreshold;
   private State state;
@@ -195,7 +198,7 @@ public class DefaultCircuitBreaker implements CircuitBreaker {
     this.failureCount = 0;
   }
 
-  //Reset everything to defaults
+  // Reset everything to defaults
   @Override
   public void recordSuccess() {
     this.failureCount = 0;
@@ -204,12 +207,14 @@ public class DefaultCircuitBreaker implements CircuitBreaker {
   }
 
   @Override
-  public void recordFailure() {
+  public void recordFailure(String response) {
     failureCount = failureCount + 1;
     this.lastFailureTime = System.nanoTime();
+    // Cache the failure response for returning on open state
+    this.lastFailureResponse = response;
   }
 
-  //Evaluate the current state based on failureThreshold, failureCount and lastFailureTime.
+  // Evaluate the current state based on failureThreshold, failureCount and lastFailureTime.
   protected void evaluateState() {
     if (failureCount >= failureThreshold) { //Then something is wrong with remote service
       if ((System.nanoTime() - lastFailureTime) > retryTimePeriod) {
@@ -263,8 +268,8 @@ public class DefaultCircuitBreaker implements CircuitBreaker {
   public String attemptRequest() throws RemoteServiceException {
     evaluateState();
     if (state == State.OPEN) {
-      // return  cached response if no the circuit is in OPEN state
-      return "This is stale response from API";
+      // return cached response if the circuit is in OPEN state
+      return this.lastFailureResponse;
     } else {
       // Make the API request if the circuit is not OPEN
       try {
@@ -276,13 +281,12 @@ public class DefaultCircuitBreaker implements CircuitBreaker {
         recordSuccess();
         return response;
       } catch (RemoteServiceException ex) {
-        recordFailure();
+        recordFailure(ex.getMessage());
         throw ex;
       }
     }
   }
 }
-
 ```
 
 How does the above pattern prevent failures? Let's understand via this finite state machine 

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

@@ -69,12 +69,10 @@ public static void main(String[] args) {
     var serverStartTime = System.nanoTime();
 
     var delayedService = new DelayedRemoteService(serverStartTime, 5);
-    //Set the circuit Breaker parameters
     var delayedServiceCircuitBreaker = new DefaultCircuitBreaker(delayedService, 3000, 2,
         2000 * 1000 * 1000);
 
     var quickService = new QuickRemoteService();
-    //Set the circuit Breaker parameters
     var quickServiceCircuitBreaker = new DefaultCircuitBreaker(quickService, 3000, 2,
         2000 * 1000 * 1000);
 
@@ -99,6 +97,7 @@ public static void main(String[] args) {
 
     //Wait for the delayed service to become responsive
     try {
+      LOGGER.info("Waiting for delayed service to become responsive");
       Thread.sleep(5000);
     } catch (InterruptedException e) {
       e.printStackTrace();

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

@@ -28,18 +28,18 @@
  */
 public interface CircuitBreaker {
 
-  //Success response. Reset everything to defaults
+  // Success response. Reset everything to defaults
   void recordSuccess();
 
-  //Failure response. Handle accordingly and change state if required.
-  void recordFailure();
+  // Failure response. Handle accordingly with response and change state if required.
+  void recordFailure(String response);
 
-  //Get the current state of circuit breaker
+  // Get the current state of circuit breaker
   String getState();
 
-  //Set the specific state manually.
+  // Set the specific state manually.
   void setState(State state);
 
-  //Attempt to fetch response from the remote service.
+  // Attempt to fetch response from the remote service.
   String attemptRequest() throws RemoteServiceException;
 }

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

@@ -24,9 +24,8 @@
 package com.iluwatar.circuitbreaker;
 
 /**
- * The delay based Circuit breaker implementation that works in a
- * CLOSED->OPEN-(retry_time_period)->HALF_OPEN->CLOSED flow with some retry time period for failed
- * services and a failure threshold for service to open
+ * The delay based Circuit breaker implementation that works in a CLOSED->OPEN-(retry_time_period)->HALF_OPEN->CLOSED
+ * flow with some retry time period for failed services and a failure threshold for service to open
  * circuit.
  */
 public class DefaultCircuitBreaker implements CircuitBreaker {
@@ -35,6 +34,7 @@ public class DefaultCircuitBreaker implements CircuitBreaker {
   private final long retryTimePeriod;
   private final RemoteService service;
   long lastFailureTime;
+  private String lastFailureResponse;
   int failureCount;
   private final int failureThreshold;
   private State state;
@@ -64,7 +64,7 @@ public class DefaultCircuitBreaker implements CircuitBreaker {
     this.failureCount = 0;
   }
 
-  //Reset everything to defaults
+  // Reset everything to defaults
   @Override
   public void recordSuccess() {
     this.failureCount = 0;
@@ -73,12 +73,14 @@ public void recordSuccess() {
   }
 
   @Override
-  public void recordFailure() {
+  public void recordFailure(String response) {
     failureCount = failureCount + 1;
     this.lastFailureTime = System.nanoTime();
+    // Cache the failure response for returning on open state
+    this.lastFailureResponse = response;
   }
 
-  //Evaluate the current state based on failureThreshold, failureCount and lastFailureTime.
+  // Evaluate the current state based on failureThreshold, failureCount and lastFailureTime.
   protected void evaluateState() {
     if (failureCount >= failureThreshold) { //Then something is wrong with remote service
       if ((System.nanoTime() - lastFailureTime) > retryTimePeriod) {
@@ -132,8 +134,8 @@ public void setState(State state) {
   public String attemptRequest() throws RemoteServiceException {
     evaluateState();
     if (state == State.OPEN) {
-      // return  cached response if no the circuit is in OPEN state
-      return "This is stale response from API";
+      // return cached response if the circuit is in OPEN state
+      return this.lastFailureResponse;
     } else {
       // Make the API request if the circuit is not OPEN
       try {
@@ -145,7 +147,7 @@ public String attemptRequest() throws RemoteServiceException {
         recordSuccess();
         return response;
       } catch (RemoteServiceException ex) {
-        recordFailure();
+        recordFailure(ex.getMessage());
         throw ex;
       }
     }

circuit-breaker/src/test/java/com/iluwatar/circuitbreaker/AppTest.java

@@ -27,12 +27,16 @@
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * App Test showing usage of circuit breaker.
  */
 public class AppTest {
 
+  private static final Logger LOGGER = LoggerFactory.getLogger(AppTest.class);
+
   //Startup delay for delayed service (in seconds)
   private static final int STARTUP_DELAY = 4;
 
@@ -79,7 +83,7 @@ public void testFailure_OpenStateTransition() {
     //As failure threshold is "1", the circuit breaker is changed to OPEN
     assertEquals("OPEN", delayedServiceCircuitBreaker.getState());
     //As circuit state is OPEN, we expect a quick fallback response from circuit breaker.
-    assertEquals("This is stale response from API", monitoringService.delayedServiceResponse());
+    assertEquals("Delayed service is down", monitoringService.delayedServiceResponse());
 
     //Meanwhile, the quick service is responding and the circuit state is CLOSED
     assertEquals("Quick Service is working", monitoringService.quickServiceResponse());
@@ -96,6 +100,7 @@ public void testFailure_HalfOpenStateTransition() {
 
     //Waiting for recovery period of 2 seconds for circuit breaker to retry service.
     try {
+      LOGGER.info("Waiting 2s for delayed service to become responsive");
       Thread.sleep(2000);
     } catch (InterruptedException e) {
       e.printStackTrace();
@@ -114,6 +119,7 @@ public void testRecovery_ClosedStateTransition() {
 
     //Waiting for 4 seconds, which is enough for DelayedService to become healthy and respond successfully.
     try {
+      LOGGER.info("Waiting 4s for delayed service to become responsive");
       Thread.sleep(4000);
     } catch (InterruptedException e) {
       e.printStackTrace();