Question: Multi Threaded Routing Module Servelet

How do you create a multi-threaded routing module servelet so all available CPU cores are utilised?

Also in the routing module servelet how do you make a distinction on what type of request is made when the method is not provided? Within this context how can parameters be accessed?

[eduard-vasinskyi]

Hello, @sirinath RouterModule is supported only for single-threaded servers. You have to map servlets to corresponding paths by hand, similarly to example from this reply

// Also at this point if I want to read a cookie how do I do it?

You can read a cookie directly from a request by calling either @Nullable String getCookie(String) - to read a single cookie or Map<String,String> getCookies() - to retrieve all of the cookies from a request

You can refer to API of HttpRequest if you need help with accessing cookies or other request parameters. Or you can look at examples on the website that I have provided in previous reply.

Also, what does this piece of code do in the example on your site

Modules.combine() allows you to combine bindings from different modules as if it is a single module. If your application has several modules, you could use Modules.combine() to return a single module from getBusinessLogicModule() method or getOverrideModule().

Also how does getBusinessLogicModule() compare with getOverrideModule()?

If you specify a duplicate binding in getBusinessLogicModule() you will catch an exception, as bindings with same keys are forbidden. However, if you want to override existing bindings with your own, you can use getOverrideModule() for this. For example, you can override default Config provided in HttpServerLauncher by overriding getOverrideModule() and returning a module that contains binding for a new Config.

You can refer to documentation for more information. Or you can look at API/javadocs of Injector, Launcher or HttpServerLauncher

[eduard-vasinskyi]

Hello, @sirinath Yes, you can use routing servlet in multithreaded context. The preffered way is to specify all of the mappings directly. If you wish, you can omit HTTP method while configuring routes in RoutingServlet. You can determine a method of HTTP request based on result of request.getMethod() call. But it is more convenient to specify the method to be handled. Mappings that do not specify HTTP method are primarly useful for providing fallback servlets, or for combining with other routing servlets that have mappings for multiple methods.

Here is a snippet that demonstrates how to do that:

package io.activej.launchers.http;

import io.activej.http.AsyncServlet;
import io.activej.http.HttpResponse;
import io.activej.http.RoutingServlet;
import io.activej.inject.Injector;
import io.activej.inject.annotation.Named;
import io.activej.inject.annotation.Provides;
import io.activej.worker.annotation.Worker;
import io.activej.worker.annotation.WorkerId;

import static io.activej.http.HttpMethod.GET;
import static io.activej.http.HttpMethod.POST;

public final class ApplicationLauncher extends MultithreadedHttpServerLauncher {

	@Provides
	@Worker
	AsyncServlet servlet(@WorkerId int workerId, @Named("API") AsyncServlet apiServlet) {
		return RoutingServlet.create()
				.map(GET, "/", request -> HttpResponse.ok200()
						.withPlainText("hello world: " + workerId))
				.map("/allMethods", request -> HttpResponse.ok200()
						.withPlainText("Called with HTTP method: " + request.getMethod()))
				.map("/api/*", apiServlet);
	}

	@Provides
	@Worker
	@Named("API")
	AsyncServlet apiServlet(@WorkerId int workerId) {
		return RoutingServlet.create()
				.map(GET, "/resource", request -> HttpResponse.ok200()
						.withPlainText("Getting a resource from worker: " + workerId))
				.map(POST, "/resource", request -> HttpResponse.ok200()
						.withPlainText("Posting a resource to worker: " + workerId));
	}

	public static void main(String[] args) throws Exception {
		Injector.useSpecializer();

		new ApplicationLauncher().launch(args);
	}
}

Note how HTTP method of the request is accessed in /allMethods mapping. An API servlet that has mappings for different methods is mapped to /api/* endpoint that does not specify HTTP method. As a result, requests are correctly passed to the API servlet to be handled.

To learn more about servlets and how parameters are handled, please refer to examples: Multithreaded server Request parameters Routing servlet