Real time questions

1) If multiple requests are send to client/user then some requests are failed then what we do in java

If multiple requests are sent to a client/user then some of them are fail, there are multiple ways to handle or recover from those failures in Java, depending on the context (e.g., REST API calls, async processing, messaging systems, etc.).

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✅ Common Scenarios and Solutions in Java

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1. Retry Mechanism

If a request fails due to a transient error (e.g., network timeout, 500 error), you can retry:

int maxRetries = 3;
int attempt = 0;
boolean success = false;

while (attempt < maxRetries && !success) {
    try {
        sendRequest();  // custom method
        success = true;
    } catch (Exception e) {
        attempt++;
        if (attempt == maxRetries) {
            System.out.println("All retries failed.");
        }
    }
}

👉 For real-world use, libraries like Spring Retry, Resilience4j, or Hystrix can help.

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2. Logging and Alerting

Always log failures for analysis and alert if the failure is critical.

java
catch (Exception e) {
    logger.error("Request failed: ", e);
    // sendAlertEmail(e); or push to monitoring tool
}

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3. Fallback / Default Response

Provide a default response if the main logic fails (used in service-to-service calls).

java
try {
    return callAnotherService();
} catch (Exception e) {
    return getFallbackResponse();  // return default data or cached result
}

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4. Asynchronous Handling with Future/CompletableFuture

Handle multiple requests asynchronously and collect results individually:

java
List<CompletableFuture<String>> futures = urls.stream()
    .map(url -> CompletableFuture.supplyAsync(() -> makeRequest(url)))
    .collect(Collectors.toList());

for (CompletableFuture<String> future : futures) {
    try {
        System.out.println(future.get());
    } catch (Exception e) {
        System.out.println("Request failed for one URL");
    }
}

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5. Dead Letter Queue (DLQ) (For Messaging/Kafka Use Cases)

When using message brokers like Kafka or RabbitMQ, failed messages are sent to a DLQ for later reprocessing.

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6. Circuit Breaker Pattern (with Resilience4j/Hystrix)

Avoid overloading a failing system by "breaking the circuit" temporarily:

java
// Using Resilience4j
CircuitBreaker circuitBreaker = CircuitBreaker.ofDefaults("myService");
Supplier<String> decorated = CircuitBreaker
    .decorateSupplier(circuitBreaker, () -> callRemoteService());

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✅ What Should You Do When Requests Fail?

Step	What to Do
Detect failure	Use try-catch, response codes
Log error	Log for audit/debug
Retry	Use retries for transient issues
Fallback	Use default response or cache
Async handling	Don't block main thread
Circuit breaker	Avoid cascading failures
DLQ or Queue retry	For messaging-based architecture

2)If multiple requests are send to client/user then some responses are failed then what we do in java

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When multiple responses fail after sending multiple requests to a client/user (or from a client to a server), the key actions you take in Java depend on:

1. The type of system (web app, REST client, messaging app, etc.)

2. The reason for failure (timeouts, exceptions, invalid data)

3. The business requirement (retry, fallback, alert, skip, etc.)

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✅ Common Actions to Take When Some Responses Fail in Java

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1. Retry Failed Responses

If failures are temporary (e.g., network issue, server overload), retrying helps.

java
public String sendWithRetry(Supplier<String> request, int maxRetries) {
    int attempt = 0;
    while (attempt < maxRetries) {
        try {
            return request.get(); // Make the call
        } catch (Exception e) {
            attempt++;
        }
    }
    return "Failed after retries";
}

✅ Use libraries like Spring Retry or Resilience4j Retry for production-level retries.

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2. Handle Each Response Individually (Graceful Degradation)

If you're sending multiple parallel requests and some fail:

java
List<String> urls = List.of("url1", "url2", "url3");

for (String url : urls) {
    try {
        String response = sendRequest(url);
        System.out.println("Success: " + response);
    } catch (Exception e) {
        System.out.println("Failed for: " + url);
    }
}

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3. Use Asynchronous Requests with Fallbacks

Using CompletableFuture:

java
List<CompletableFuture<String>> futures = urls.stream()
    .map(url -> CompletableFuture.supplyAsync(() -> {
        try {
            return sendRequest(url);
        } catch (Exception e) {
            return "Fallback for " + url;
        }
    }))
    .collect(Collectors.toList());

futures.forEach(f -> System.out.println(f.join()));

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4. Log Failures for Analysis

Always log failures for future investigation:

java
catch (Exception e) {
    logger.error("Request failed", e);
}

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5. Notify User or Client Gracefully

Instead of crashing the app, send a partial success response or notify user:

java
return ResponseEntity
    .status(HttpStatus.PARTIAL_CONTENT)
    .body("Some requests failed, but others succeeded.");

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6. Circuit Breaker (Avoid Repeated Failures)

Use Resilience4j or Hystrix:

java
CircuitBreaker cb = CircuitBreaker.ofDefaults("externalService");
Supplier<String> protectedCall = CircuitBreaker
    .decorateSupplier(cb, () -> sendRequest("url"));

try {
    String result = protectedCall.get();
} catch (Exception e) {
    System.out.println("Circuit is open, fallback response used.");
}

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✅ Summary Table: What to Do When Some Responses Fail

Action	Description
✅ Retry	Retry failed requests (limited times)
✅ Fallback	Provide default response when real one fails
✅ Async Execution	Don't block whole system due to partial failure
✅ Log & Monitor	Log failures for alerting and analysis
✅ Notify User Gracefully	Inform user that partial success occurred
✅ Circuit Breaker	Avoid repeated calls to known-failing services
✅ Skip & Continue	Skip failed requests and continue with others

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