implement retry template

implement exponential backoff strategy

lottery-consumer-service/src/main/java/com/example/lottery/config/RetryTemplateConfig.java

@@ -0,0 +1,29 @@
+package com.example.lottery.config;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.retry.backoff.ExponentialBackOffPolicy;
+import org.springframework.retry.policy.SimpleRetryPolicy;
+import org.springframework.retry.support.RetryTemplate;
+
+/**
+ * 
+ * @author Binnur Kurt <binnur.kurt@gmail.com>
+ *
+ */
+@Configuration
+public class RetryTemplateConfig {
+	@Bean
+	public RetryTemplate retryTemplate() {
+		RetryTemplate retryTemplate = new RetryTemplate();
+
+		ExponentialBackOffPolicy exponentialBackOffPolicy = new ExponentialBackOffPolicy();
+		exponentialBackOffPolicy.setInitialInterval(1000L);
+		retryTemplate.setBackOffPolicy(exponentialBackOffPolicy);
+
+		SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy();
+		retryPolicy.setMaxAttempts(3);
+		retryTemplate.setRetryPolicy(retryPolicy);
+		return retryTemplate;
+	}
+}

lottery-consumer-service/src/main/java/com/example/lottery/service/LotteryConsumerServiceWithRetryTemplate.java

@@ -0,0 +1,43 @@
+package com.example.lottery.service;
+
+import java.util.List;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.retry.RecoveryCallback;
+import org.springframework.retry.RetryCallback;
+import org.springframework.retry.support.RetryTemplate;
+import org.springframework.scheduling.annotation.Scheduled;
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestTemplate;
+
+import com.example.lottery.dto.LotteryResponse;
+
+@Service
+public class LotteryConsumerServiceWithRetryTemplate {
+	@Autowired
+	private RetryTemplate retryTemplate;
+
+	@Scheduled(fixedRate = 12_000)
+	public void doSomething() {
+		RetryCallback<LotteryResponse, Exception> retryCallback = context -> {
+			System.err.println("Calling lottery service from LotteryConsumerServiceWithRetryTemplate...");
+			var rt = new RestTemplate();
+			var response = rt.getForObject("http://localhost:8001/lottery/api/v1/numbers?column=10",
+					LotteryResponse.class);
+			System.err.println(response);
+			return response;
+		};
+		RecoveryCallback<LotteryResponse> recoveryCallback = context -> {
+			System.err.println("Calling recoveryCallback from LotteryConsumerServiceWithRetryTemplate...");
+			return new LotteryResponse(List.of(List.of(5, 10, 15, 20, 25, 30)));
+		};
+		try {
+			var response = retryTemplate.execute(retryCallback, recoveryCallback);
+			System.out.println(response);
+		} catch (Exception e) {
+			System.err.println(e.getMessage());
+		}
+
+	}
+
+}

lottery-consumer-service/src/main/java/com/example/lottery/service/SimpleDemoService.java

@@ -13,6 +13,8 @@
 public class SimpleDemoService {
 	@Autowired
 	private LotteryConsumerServiceWithCircuitBreaker srv;
+	@Autowired
+	private StudyRetryStrategy retryStrategy;
 
 	@Scheduled(fixedRate = 2_000)
 	public void doSomething() {
@@ -23,4 +25,14 @@ public void doSomething() {
 					String.format("Exception (%s) in doSomething(): %s", e.getClass().getName(), e.getMessage()));
 		}
 	}
+
+	@Scheduled(fixedRate = 5_000)
+	public void doSomethingElse() {
+		try {
+			System.out.println(retryStrategy.getNumbers());
+		} catch (Exception e) {
+			System.err.println(
+					String.format("Exception (%s) in doSomething(): %s", e.getClass().getName(), e.getMessage()));
+		}
+	}
 }

lottery-consumer-service/src/main/java/com/example/lottery/service/StudyRetryStrategy.java

@@ -2,13 +2,16 @@
 
 import java.net.SocketException;
 import java.net.SocketTimeoutException;
+import java.util.List;
 
 import org.springframework.retry.annotation.Backoff;
+import org.springframework.retry.annotation.Recover;
 import org.springframework.retry.annotation.Retryable;
 import org.springframework.stereotype.Service;
 import org.springframework.web.client.RestTemplate;
 
 import com.example.lottery.dto.LotteryResponse;
+import com.google.inject.Exposed;
 
 /**
  * 
@@ -17,12 +20,18 @@
  */
 @Service
 public class StudyRetryStrategy {
-	
-	@Retryable(value= {SocketTimeoutException.class, SocketException.class},
-			maxAttempts = 3, backoff=@Backoff(delay = 3_000))
+
+	@Retryable(value = { SocketTimeoutException.class,                  // exponential backoff: 2^{n} * 3 seconds
+			SocketException.class }, maxAttempts = 3, backoff = @Backoff(multiplier = 2, delay = 3_000))
 	public LotteryResponse getNumbers() {
 		System.err.println("Calling lottery service from StudyRetryStrategy...");
 		RestTemplate rt = new RestTemplate();
 		return rt.getForObject("http://localhost:8001/lottery/api/v1/numbers?column=10", LotteryResponse.class);
 	}
+
+	@Recover
+	public LotteryResponse getNumbersFallback(Exception e) {
+		return new LotteryResponse(List.of(List.of(1, 3, 5, 7, 9, 11), List.of(2, 4, 6, 8, 10, 12)));
+	}
+
 }