How to implement asynchronous retry mechanism in java 8? - spring-boot

Question

I'm using Java 8 Spring boot. I have below method.
public hello() {
try {
// send message
}
catch(HttpClientErrorException e) {
if (e.getRawStatusCode() == 401) {
// I need to retry the same hello() method for three times as in 10sec, 20sec and 25sec.
}
}
}
I need to call the same method three times for retrying whenever it hits the catch block.
How can I do this asynchronously?
I found below code but it didn't work.
#Retryable( value = {RestClientException.class}, maxAttempts = 3, backoff = #Backoff(3000))
Appreciate your help.

Answer 1

You can use #Async annotation from Spring to achieve that.
You have to create a config like this:
#Configuration
#EnableRetry
#EnableAsync
class RetryConfig {}
When you want to use Async with Retry you have to decorate the method with Async which is trying to call a Retryable method. Also, you have to make sure that you are returning Future<> or similar because you are sending that piece of code for a toss in the background
I have also implemented fallback mechanism otherwise the request will terminate with 500 exception.
If you run the code below you can see that the main request is executed on thread http-nio-8080-exec-1 while your Async code is executed on a different thread task-1.
I tried to explain this with a sample service method, but the concept will be same for local or remote service call.
A detailed exmaple is given below:
package com.example.silentsudo.springcloudssamples;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Configuration;
import org.springframework.retry.annotation.Backoff;
import org.springframework.retry.annotation.EnableRetry;
import org.springframework.retry.annotation.Recover;
import org.springframework.retry.annotation.Retryable;
import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import java.util.concurrent.CompletableFuture;
#SpringBootApplication
public class SpringCloudsSamplesApplication {
public static void main(String[] args) {
SpringApplication.run(SpringCloudsSamplesApplication.class, args);
}
}
#RequestMapping(path = "sample")
#RestController
class SampleController {
private final GreetService greetService;
SampleController(GreetService greetService) {
this.greetService = greetService;
}
#GetMapping
public String hello() {
System.out.println(Thread.currentThread().getName());
return "Hello!";
}
#GetMapping(path = "greet")
public String greet(#RequestParam(value = "name", defaultValue = "John") String name) {
return greetService.greet(name);
}
#Async
#GetMapping(path = "greet-async")
public CompletableFuture<String> greetAsync(#RequestParam(value = "name", defaultValue = "John") String name) {
return CompletableFuture.completedFuture(greetService.greet(name));
}
}
#Configuration
#EnableRetry
#EnableAsync
class RetryConfig {
}
#Service
class GreetService {
private final UngaBungaService ungaBungaService;
GreetService(UngaBungaService ungaBungaService) {
this.ungaBungaService = ungaBungaService;
}
#Retryable(maxAttempts = 5, value = GreetException.class, backoff = #Backoff(value = 3000L))
public String greet(String name) {
return ungaBungaService.lol(name);
}
#Recover
public String recoverGreetException(GreetException greetException) {
return greetException.getMessage();
}
}
#Service
class UngaBungaService {
public String lol(String name) {
System.out.println(Thread.currentThread().getName());
throw new GreetException("Called greet for " + name);
}
}
class GreetException extends RuntimeException {
public GreetException(String message) {
super(message);
}
}

Answer 2

For retry mechanisms, you can to use the #Retryable(value = RestClientException.class)
For this to trigger, you need to actually throw this exception (or something that extends from RestClientException). Because of your catch statement, no exception is actually thrown, so the retry mechanism doesn't kick in.
#Retryable( value = {RestClientException.class}, maxAttempts = 3, backoff = #Backoff(3000))
public void hello() {
try {
// send message
}
catch(HttpClientErrorException e) {
if (e.getRawStatusCode() == 401) {
throw new RestClientException("meaningfull message");
}
}
}
If you want to run some catch code after the 3 retries failed, you can make use of the #Recover annotation on a recovery method.
If you want some more info on the retry mechanism, you could look here
Also don't forget to add #EnableRetry in your config so that the annotations are used.
Full code example with spring boot
#SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(DemoApplication.class, args);
context.getBean(TestService.class).hello();
context.close();
}
#Configuration
#EnableRetry
public class AppConfig {
}
#Service
public class TestService {
#Retryable(value = {IllegalArgumentException.class}, maxAttempts = 4, backoff = #Backoff(delay = 1000, multiplier = 4))
public void hello() {
try {
int a = Integer.parseInt(null);
} catch (NumberFormatException e) {
throw new IllegalArgumentException("Exception triggered");
}
}
}