Interview question

What are best practices for logging and debugging exceptions in production Java applications? Production Java applications में exceptions log और debug करने की best practices क्या हैं?

Answer

Practice	Why it matters
Use a logging framework (SLF4J, Log4j), not System.out	Configurable levels, output destinations, and performance
Log the full stack trace	Root cause is often deep in the chain, not just the top message
Never swallow exceptions silently	Empty catch blocks hide real problems
Include context in log messages	User ID, request ID, operation name help correlate issues

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

class OrderService {
    private static final Logger logger = LoggerFactory.getLogger(OrderService.class);

    public void processOrder(String orderId) {
        try {
            // ... processing logic ...
        } catch (Exception e) {
            // GOOD: logs message, context, AND full stack trace
            logger.error('Failed to process order {}: {}', orderId, e.getMessage(), e);
            throw new RuntimeException('Order processing failed', e);  // rethrow, don't swallow
        }
    }
}

// BAD PRACTICE - silently swallowing exceptions
public void badExample() {
    try {
        riskyOperation();
    } catch (Exception e) {
        // empty catch block - error disappears completely, very hard to debug later
    }
}

// BAD PRACTICE - printStackTrace() only, no structured logging
catch (Exception e) {
    e.printStackTrace();  // goes to console only, lost in production, no log levels
}

// GOOD - catching specific exceptions, not blanket 'catch (Exception e)' everywhere
try {
    parseInput(data);
} catch (NumberFormatException e) {
    logger.warn('Invalid number format in input: {}', data);
} catch (IllegalArgumentException e) {
    logger.warn('Invalid argument: {}', e.getMessage());
}
// Blanket catches make it hard to know what specifically went wrong

Practice	क्यों important है
Logging framework use करना, System.out नहीं	Configurable levels, destinations
पूरा stack trace log करना	Root cause अक्सर chain में गहरा होता है
Exceptions चुपचाप swallow न करना	Empty catch blocks real problems छुपाते हैं
Log messages में context शामिल करना	User ID, request ID debugging में मदद करते हैं

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

class OrderService {
    private static final Logger logger = LoggerFactory.getLogger(OrderService.class);

    public void processOrder(String orderId) {
        try {
            // ... processing ...
        } catch (Exception e) {
            logger.error('Failed to process order {}: {}', orderId, e.getMessage(), e);
            throw new RuntimeException('Order processing failed', e);
        }
    }
}

// गलत practice - चुपचाप swallow करना
public void badExample() {
    try {
        riskyOperation();
    } catch (Exception e) {
        // empty catch block - error पूरी तरह गायब हो जाती है
    }
}

// गलत practice - सिर्फ printStackTrace()
catch (Exception e) {
    e.printStackTrace();  // production में खो जाता है
}

// सही - specific exceptions catch करना
try {
    parseInput(data);
} catch (NumberFormatException e) {
    logger.warn('Invalid number format: {}', data);
} catch (IllegalArgumentException e) {
    logger.warn('Invalid argument: {}', e.getMessage());
}

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