Configuring Servlets

Servlets with Microservices and Micro-monoliths

Microserver services can all run in true Microservice stand-alone style, or Microserver allows multiple otherwise independent services to be bundled together at runtime to act as a 'micro'-monolith.

Autodiscovered Servlets, are discovered within the shared Spring context, and thus (currently) become globally available to all bundled microservices. If you are not bundling services - this is not significant, but if you are, or are planning to - it is something to be mindful of.

Servlets can be configured locally via the Module interface (when you start your Microservice),or by the Plugin interface.

Configuring Global Servlets

These Servlets will be available on all Microservices sharing a core Spring context.

In order to automagically add a Servlet to your Microservice, implement the interface ServletConfiguration on a Spring bean. If the bean implementing ServletConfiguration is also a Servle only the method getMapping() need be implemented. This will be the context URL of your Servlet.

         public Class<? extends Servlet> getServlet()

Override the above method to configure a specified Servlet class. Typically used for Servlets in external jar files.

         public String getName()

To change the Servlet name to something other than the Class name.

         public Map<String,String> getInitParameters()

To configure the init parameters for the Servlet

        public Map<String,String> getInitParameters(){
		return ImmutableMap.of();
	}

    @Component
    public class AutodiscoveredServlet extends HttpServlet 
                           implements ServletConfiguration {

	@Override
	public String[] getMapping() {
		return new String[] { "/servlet" };
	}

	@Override
	protected void doGet(HttpServletRequest req, 
                                 HttpServletResponse resp)
			throws ServletException, IOException {

		resp.setContentType("text/html");
		resp.getWriter().write("hello world");
	}
    }

#Configuring Local Servlets

These Servlets will only be available on the Microservice modules they are configured against.

In your Module object override

     public Map<String,Servlet> getServlets()

To configure module local servlets and their contexts Urls .

     public Class<? extends ServletConfiguration>[] getServletConfigurationClass()

Configuring Servlets in a Plugin

Servlets can be configured inside a plugin both as explicitly defined Servlets, or as auto discovered Spring Beans that implement ServletConfiguration.

Override the filters method to provide a lookup function for the Servlets

	public Function<ServerData,Map<String,Servlet>> servlets(){
		return serverData -> myMapOfFilters;
	}

or override springClasses and add your ServletConfiguration Spring beans there

        public Set<Class> springClasses(){
		return new HashSet<>();
	}