31. Interceptor In CSHARP

Tags:CSharpAOPProgramming

What is an Interceptor?

A mechanism to modify or enhance method calls without changing the original code. Used for cross-cutting concerns (logging, caching, validation) via Aspect-Oriented Programming (AOP).

How It Works

1. Proxy Objects: Libraries (e.g., Castle.DynamicProxy) generate proxy classes wrapping your objects.
2. Intercept Calls: Inject logic before/after method execution.
3. Common Workflow:
   • Pre-process (e.g., validate inputs).
   • Execute the original method.
   • Post-process (e.g., log results).

---

Example: Logging Interceptor

// Interceptor class
public class LoggingInterceptor : IInterceptor  
{  
    public void Intercept(IInvocation invocation)  
    {  
        Console.WriteLine($"START: {invocation.Method.Name}");  
        invocation.Proceed(); // Run the original method  
        Console.WriteLine($"END: {invocation.Method.Name}");  
    }  
}  
 
// Usage  
var proxy = new ProxyGenerator()  
    .CreateClassProxy<MyService>(new LoggingInterceptor());  
proxy.DoWork();  

Output:

START: DoWork  
Working...  
END: DoWork  

---

Use Cases

• Logging: Track method calls/results.
• Caching: Store results of expensive calls.
• Validation: Check inputs before execution.
• Retry Logic: Automatically retry failed operations.

Key Benefits

• ✅ Separation of Concerns: Core logic stays clean.
• ✅ Reusable: Apply to multiple methods/classes.
• ✅ Non-Invasive: No changes to existing code.

Popular Libraries

• Castle.DynamicProxy
• PostSharp
• Unity.Interception (for DI containers)