Asp.net-core – ASP.NET Core Web API Logging from a Static Class

asp.net-coreasp.net-core-webapidependency-injectionloggingstatic-classes

I'm logging just fine using dependency injection on my controllers, now I need to log something from a static class.

How can I log from a static class?

I can't use dependency injection because it's static and I can't just pass in an existing logger object to the static class because it would have the wrong name of class in the log file.

In other words how can I get a logger from the loggerfactory inside my static class?

I came across a similar question and they pointed to an article on a loggerfactory in a static class but that doesn't actually work as I can't get a new logger from it because it won't accept a static class as the parameter:

"Static types cannot be used as type arguments"

Best Answer

Solution is to have a static reference to the LoggerFactory in a utility static class initialized on startup:

/// <summary>
    /// Shared logger
    /// </summary>
    internal static class ApplicationLogging
    {
        internal static ILoggerFactory LoggerFactory { get; set; }// = new LoggerFactory();
        internal static ILogger CreateLogger<T>() => LoggerFactory.CreateLogger<T>();        
        internal static ILogger CreateLogger(string categoryName) => LoggerFactory.CreateLogger(categoryName);

    }

Which you intialize on Startup.cs:

 public Startup(ILogger<Startup> logger, ILoggerFactory logFactory, IHostingEnvironment hostingEnvironment)
        {
            _log = logger;
            _hostingEnvironment = hostingEnvironment;
            Util.ApplicationLogging.LoggerFactory = logFactory;//<===HERE

        }

Then you can build a logger to use from your static class like so:

internal static class CoreJobSweeper
    {
        private static ILogger log = Util.ApplicationLogging.CreateLogger("CoreJobSweeper");

Related Solutions

Java inner class and static nested class

From the Java Tutorial:

Nested classes are divided into two categories: static and non-static. Nested classes that are declared static are simply called static nested classes. Non-static nested classes are called inner classes.

Static nested classes are accessed using the enclosing class name:

OuterClass.StaticNestedClass

For example, to create an object for the static nested class, use this syntax:

OuterClass.StaticNestedClass nestedObject = new OuterClass.StaticNestedClass();

Objects that are instances of an inner class exist within an instance of the outer class. Consider the following classes:

class OuterClass {
    ...
    class InnerClass {
        ...
    }
}

An instance of InnerClass can exist only within an instance of OuterClass and has direct access to the methods and fields of its enclosing instance.

To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax:

OuterClass outerObject = new OuterClass()
OuterClass.InnerClass innerObject = outerObject.new InnerClass();

see: Java Tutorial - Nested Classes

For completeness note that there is also such a thing as an inner class without an enclosing instance:

class A {
  int t() { return 1; }
  static A a =  new A() { int t() { return 2; } };
}

Here, new A() { ... } is an inner class defined in a static context and does not have an enclosing instance.

C# – Dependency injection with a static logger, static helper class

This is not necessarily so. As long as your static logger exposes a method for:

Injection of the classes you WANT injected, or
Injection of the DI Container in an appropriate method call prior to running it (say in something like the asp.net global.asax Application_Start method), then you should be fine.

Here's an example. Take the following class for DI:

 public class Logger : ILogger
    {
        public void Log(string stringToLog)
        {
           Console.WriteLine(stringToLog);
        }
    }

    public interface ILogger
    {
        void Log(string stringToLog);
    }

And here's our static class which needs a logger:

public static class SomeStaticClass
    {
        private static IKernel _diContainer;
        private static ILogger _logger;

        public static void Init(IKernel dIcontainer)
        {
            _diContainer = dIcontainer;
            _logger = _diContainer.Get<ILogger>();
        }


        public static void Log(string stringToLog)
        {
            _logger.Log(stringToLog);
        }


    }

Now, in a global startup for your app (in this case, in my global.asax.cs), you can instantiate your DI Container, then hand that off to your static class.

public class Global : Ninject.Web.NinjectHttpApplication
    {

        protected override IKernel CreateKernel()
        {
            return Container;
        }


        static IKernel Container
        {
            get
            {
                var standardKernel = new StandardKernel();
                standardKernel.Bind<ILogger>().To<Logger>();
                return standardKernel;
            }

        }

        void Application_Start(object sender, EventArgs e)
        {
            SomeStaticClass.Init(Container);
            SomeStaticClass.Log("Dependency Injection with Statics is totally possible");

        }

And presto! You are now up and running with DI in your static classes.

Hope that helps someone. I am re-working an application which uses a LOT of static classes, and we've been using this successfully for a while now.

Best Answer

Related Solutions

Java inner class and static nested class

C# – Dependency injection with a static logger, static helper class

Related Topic