การใช้ Fallback และ Timeout

Building Resilient Services

Dealing with Unreliable Calls

Understanding Call Timeouts

Configuring Basic Timeouts

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
import org.springframework.boot.web.client.RestTemplateBuilder;
import java.time.Duration;

@SpringBootApplication
public class TimeoutApp {

  public static void main(String[] args) {
    SpringApplication.run(TimeoutApp.class, args);
  }

  @Bean
  public RestTemplate restTemplate(RestTemplateBuilder builder) {
    return builder
        .setConnectTimeout(Duration.ofSeconds(1)) // 1 second to connect
        .setReadTimeout(Duration.ofSeconds(2))    // 2 seconds to read data
        .build();
  }
  
  // In a real app, you'd inject and use this RestTemplate
  // e.g., restTemplate.getForObject("http://localhost:8081/slow-service", String.class);
}

Graceful Degradation with Fallbacks

Simple Fallback Logic

public class UserService {

  public String getUserName(int userId) {
    try {
      // Simulate a network call that might fail
      if (userId == 101) {
        throw new RuntimeException("Service unavailable!");
      }
      return "User " + userId + " Details";
    } catch (Exception e) {
      // This is our fallback logic!
      System.out.println("Error fetching user " + userId + ". Returning default.");
      return "Guest User"; // Fallback value
    }
  }

  public static void main(String[] args) {
    UserService service = new UserService();
    System.out.println(service.getUserName(100)); // Works
    System.out.println(service.getUserName(101)); // Fails, returns fallback
  }
}

Resilience4j for Fallbacks

Declarative Fallbacks with Resilience4j

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.stereotype.Service;
import org.springframework.beans.factory.annotation.Autowired;
import io.github.resilience4j.circuitbreaker.annotation.CircuitBreaker;

@SpringBootApplication
@RestController
public class ResilienceApp {

  @Autowired
  private ProductService productService;

  public static void main(String[] args) {
    SpringApplication.run(ResilienceApp.class, args);
  }

  @GetMapping("/product-info")
  public String getProductDetails() {
    return productService.getProduct();
  }
}

@Service
class ProductService {
  private int callCount = 0;

  @CircuitBreaker(name = "productService", fallbackMethod = "fallbackGetProduct")
  public String getProduct() {
    callCount++;
    if (callCount % 3 != 0) { // Simulate failure 2 out of 3 times
      throw new RuntimeException("Product service is down!");
    }
    return "Product A Details";
  }

  // This is the fallback method
  public String fallbackGetProduct(Throwable t) {
    System.out.println("Fallback activated: " + t.getMessage());
    return "Default Product (Fallback)";
  }
}

Apply Your Knowledge

Lesson Summary