Overview
Ensuring consistent error reporting and messaging across an entire codebase is crucial for effective debugging and maintenance. In the context of exception handling, this entails adopting a systematic approach to how exceptions are thrown, caught, and logged. It improves the readability of the code, makes it easier to diagnose issues, and ensures that similar errors are handled in a uniform manner.
Key Concepts
- Centralized Exception Handling: Implementing a single point in the application where all exceptions are handled.
- Custom Exception Classes: Defining application-specific exceptions that provide more context than generic exceptions.
- Logging and Monitoring: Systematically recording errors for further analysis and real-time monitoring of the application's health.
Common Interview Questions
Basic Level
- What is the purpose of custom exceptions and when should you create them?
- How does try/catch/finally construct work in C#?
Intermediate Level
- How do you implement a global exception handler in a .NET application?
Advanced Level
- Describe a strategy for logging exceptions in a distributed system. How do you ensure that error reporting is both comprehensive and not overly verbose?
Detailed Answers
1. What is the purpose of custom exceptions and when should you create them?
Answer: Custom exceptions are created to represent specific error situations that are not adequately covered by the existing exceptions in the .NET framework. They provide a way to add additional context or information related to the error, making it easier to understand the cause and impact of an exception. You should create custom exceptions when you need to differentiate between different error conditions or when standard exceptions do not convey enough information about the error.
Key Points:
- Custom exceptions give more precise information about an error.
- They allow for cleaner and more maintainable error handling code.
- Custom exceptions can carry additional properties related to the error context.
Example:
public class UserNotFoundException : Exception
{
public string Username { get; }
public UserNotFoundException(string username)
: base($"User '{username}' not found.")
{
Username = username;
}
}
2. How does try/catch/finally construct work in C#?
Answer: The try/catch/finally construct is used to handle exceptions in C#. The try block contains the code that might throw an exception. The catch block catches and handles the exception. The finally block executes after the try/catch block, regardless of whether an exception was thrown or caught, making it ideal for cleanup code.
Key Points:
- The try block is used to wrap potentially hazardous code.
- The catch block can catch specific types of exceptions, allowing for tailored handling strategies.
- The finally block is guaranteed to run, providing a secure place for cleanup activities.
Example:
try
{
// Code that may throw an exception
int[] numbers = {1, 2, 3};
Console.WriteLine(numbers[3]); // This will throw an IndexOutOfRangeException
}
catch (IndexOutOfRangeException ex)
{
// Handle the specific exception
Console.WriteLine("An index out of range error occurred.");
}
finally
{
// Cleanup code, runs no matter what
Console.WriteLine("Finally block executed.");
}
3. How do you implement a global exception handler in a .NET application?
Answer: A global exception handler in a .NET application can be implemented by attaching to the AppDomain.UnhandledException event for console applications or the Application.ThreadException event for Windows Forms applications. For ASP.NET applications, global exception handling can be achieved by overriding the Application_Error method in Global.asax.
Key Points:
- Centralizes error handling logic, making maintenance easier.
- Helps in logging uncaught exceptions at a global level.
- It's crucial for unifying the response strategy to unhandled exceptions.
Example:
class Program
{
static void Main(string[] args)
{
AppDomain.CurrentDomain.UnhandledException += GlobalExceptionHandler;
// Your application logic here
throw new Exception("Test exception");
}
static void GlobalExceptionHandler(object sender, UnhandledExceptionEventArgs e)
{
Console.WriteLine($"Unhandled exception occurred: {e.ExceptionObject}");
// Log the exception, send notifications, etc.
}
}
4. Describe a strategy for logging exceptions in a distributed system. How do you ensure that error reporting is both comprehensive and not overly verbose?
Answer: In a distributed system, a centralized logging strategy should be implemented to collect, store, and analyze logs from all services in a single place. This can be achieved through a combination of structured logging, correlation IDs for tracing requests across services, and log level management to control verbosity.
Key Points:
- Structured logging provides a uniform format (e.g., JSON) for easy parsing and analysis.
- Correlation IDs link logs from different parts of the system for a single transaction or request.
- Log levels (Debug, Info, Warning, Error, Critical) help in adjusting the verbosity dynamically based on the environment (e.g., more verbose in development, less in production).
Example:
public void LogException(Exception ex, Guid correlationId)
{
var logEntry = new
{
CorrelationId = correlationId,
Date = DateTime.UtcNow,
Level = "Error",
Message = ex.Message,
StackTrace = ex.StackTrace
};
// Assuming LogToCentralizedStorage is a method that sends the logEntry object to a centralized logging system
LogToCentralizedStorage(logEntry);
}
This approach ensures that error reporting is comprehensive by capturing all relevant details and context, while also allowing for the filtering of logs based on severity or other criteria to manage verbosity.
