In .NET Core 8, you can implement cross-cutting concerns using several techniques such as middleware, dependency injection, filters, and aspect-oriented programming (AOP). Here’s an overview of each approach:
- Middleware
Middleware components are used to handle requests and responses in ASP.NET Core applications. They can be used to implement cross-cutting concerns like logging, exception handling, and authentication.
Example: Logging Middleware
- Create a middleware class:
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public class LoggingMiddleware
{
private readonly RequestDelegate _next;
public LoggingMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task InvokeAsync(HttpContext context)
{
Console.WriteLine($"Request: {context.Request.Method} {context.Request.Path}");
await _next(context);
Console.WriteLine($"Response: {context.Response.StatusCode}");
}
}
- Register the middleware in the Startup class:
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public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
app.UseMiddleware<LoggingMiddleware>();
// Other middlewares
app.UseRouting();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllers();
});
}
- Dependency Injection (DI)
Dependency Injection allows you to inject services into your controllers, services, or other classes. This can be used to implement concerns like logging, caching, or validation.
Example: Registering a logging service
- Define the logging service interface and implementation:
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public interface ILoggerService
{
void Log(string message);
}
public class LoggerService : ILoggerService
{
public void Log(string message)
{
Console.WriteLine($"Log: {message}");
}
}
- Register the service in the Program.cs:
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var builder = WebApplication.CreateBuilder(args);
builder.Services.AddScoped<ILoggerService, LoggerService>();
var app = builder.Build();
// Configure the HTTP request pipeline.
app.UseRouting();
app.MapControllers();
app.Run();
- Inject the service into a controller:
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public class HomeController : Controller
{
private readonly ILoggerService _logger;
public HomeController(ILoggerService logger)
{
_logger = logger;
}
public IActionResult Index()
{
_logger.Log("Index action called.");
return View();
}
}
- Filters
Filters are used to run code before or after certain stages in the request processing pipeline. ASP.NET Core supports several types of filters, such as authorization, resource, action, and exception filters.
Example: Action Filter for Logging
- Create an action filter:
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public class LoggingActionFilter : IActionFilter
{
public void OnActionExecuting(ActionExecutingContext context)
{
Console.WriteLine($"Executing action: {context.ActionDescriptor.DisplayName}");
}
public void OnActionExecuted(ActionExecutedContext context)
{
Console.WriteLine($"Executed action: {context.ActionDescriptor.DisplayName}");
}
}
- Register the filter globally in Startup:
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public void ConfigureServices(IServiceCollection services)
{
services.AddControllersWithViews(options =>
{
options.Filters.Add<LoggingActionFilter>();
});
}
- Alternatively, apply the filter to a specific controller or action:
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[ServiceFilter(typeof(LoggingActionFilter))]
public class HomeController : Controller
{
public IActionResult Index()
{
return View();
}
}
- Aspect-Oriented Programming (AOP)
AOP allows you to define cross-cutting concerns separately from your business logic. Libraries like PostSharp or Castle DynamicProxy can be used for this purpose.
Example: Using Castle DynamicProxy for AOP
- Install the Castle.Core package:
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dotnet add package Castle.Core
- Create an interceptor:
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public class LoggingInterceptor : IInterceptor
{
public void Intercept(IInvocation invocation)
{
Console.WriteLine($"Intercepting: {invocation.Method.Name}");
invocation.Proceed();
Console.WriteLine($"Finished: {invocation.Method.Name}");
}
}
- Create a proxy generator:
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public class ProxyGeneratorService
{
private readonly ProxyGenerator _generator;
private readonly IInterceptor _interceptor;
public ProxyGeneratorService()
{
_generator = new ProxyGenerator();
_interceptor = new LoggingInterceptor();
}
public T CreateInterfaceProxy<T>(T instance) where T : class
{
return _generator.CreateInterfaceProxyWithTarget(instance, _interceptor);
}
}
- Use the proxy generator to create a proxy instance:
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public class HomeController : Controller
{
private readonly IMyService _myService;
public HomeController(ProxyGeneratorService proxyGenerator, IMyService myService)
{
_myService = proxyGenerator.CreateInterfaceProxy(myService);
}
public IActionResult Index()
{
_myService.DoWork();
return View();
}
}
These are some of the ways to implement cross-cutting concerns in .NET Core 8. The choice of technique depends on the specific requirements and structure of your application.