How to define isolated web contexts in a modular Spring Boot application? - spring-mvc

Question

Given a Spring Boot application comprised of a bootstrap module, and two or more isolated business modules - each of which exposes REST API specific to a business domain, and each of which uses an independent, isolated document store for data persistence, how do I go about configuring such an application, such that:
The bootstrap module defines a parent context (non-web) which provides certain shared resources to underlying modules (global config, object mappers, etc.)
Each business module exposes their REST controllers on the same port but using a different context path. Ideally, I want to be able to define a base path for each module (e.g. /api/catalog, /api/orders) and separately define the sub-path within each controller.
Each business module defines its own repository configuration (e.g. different MongoDB settings for each module)
In order to isolate the contexts of the individual business modules (which allows me to manage independent repository configurations in each module) I have tried using the context hierarchies available in SpringApplicationBuilder to isolate the contexts of each of the individual business modules:
public class Application {
#Configuration
protected static class ParentContext {
}
public static void main(String[] args) throws Exception {
new SpringApplicationBuilder(ParentContext.class)
.child(products.config.ModuleConfiguration.class)
.web(true)
.sibling(orders.config.ModuleConfiguration.class)
.web(true)
.run(args);
}
}
however as each module contains a configuration class annotated with #EnableAutoConfiguration this causes Spring Boot to attempt to launch two independent embedded servlet containers, each trying to bind to the same port:
#Configuration
#EnableAutoConfiguration
public class WebApplicationConfiguration {
#Value("${api.basePath:/api}")
protected String apiBasePath;
#Bean
public DispatcherServlet dispatcherServlet() {
return new DispatcherServlet();
}
#Bean
public ServletRegistrationBean dispatcherServletRegistration() {
ServletRegistrationBean registration = new ServletRegistrationBean(dispatcherServlet(),
apiBasePath + "/products/*");
registration.setName(DispatcherServletAutoConfiguration.DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
return registration;
}
}
The Spring Boot documentation on context hierarchies states that the parent context cannot be a web context, so I'm a bit lost as to how I can share an embedded servlet container between isolated child contexts.
I have created a minimal GitHub project to illustrate the point:

Answer 1

Create configuration class for business module child1's context
package com.child1;
#Configuration
#ComponentScan(basePackages = {"com.child1a", "com.child1b"})
public class Child1Configuration {
}
Create configuration class for business module child2's context
package com.child2;
#Configuration
#ComponentScan(basePackages = {"com.child2a", "com.child2b"})
public class Child2Configuration {
}
Create a configuration class for bootstrap module parent context. Specify the component scanning for beans to be shared by child contexts
package com.parent;
#Configuration
#ComponentScan(basePackages = {"com.parent1", "com.root"})
public class ParentConfiguration {
}
Create SpringBootApplication class with two dispatcher servlets beans, one for each business module. Create application context for each servlet and set the context created by the boot application as root. Basically spring will inject the context into the ApplicationContext parameter of the #Bean methods.
package com.parent;
#SpringBootApplication
public class Application {
public static void main(String[] args) {
ApplicationContext context = SpringApplication.run(Application.class, args);
}
#Bean
public ServletRegistrationBean child1(ApplicationContext parentContext) {
DispatcherServlet dispatcherServlet = new DispatcherServlet();
dispatcherServlet.setDetectAllHandlerMappings(false);
AnnotationConfigWebApplicationContext applicationContext = new
AnnotationConfigWebApplicationContext();
applicationContext.setParent(parentContext);
applicationContext.register(Child1Configuration.class);
applicationContext.refresh();
dispatcherServlet.setApplicationContext(applicationContext);
ServletRegistrationBean servletRegistrationBean = new
ServletRegistrationBean(dispatcherServlet, true, "/child1/*");
servletRegistrationBean.setName("child1");
servletRegistrationBean.setLoadOnStartup(1);
return servletRegistrationBean;
}
#Bean
public ServletRegistrationBean child2(ApplicationContext parentContext) {
DispatcherServlet dispatcherServlet = new DispatcherServlet();
dispatcherServlet.setDetectAllHandlerMappings(false);
AnnotationConfigWebApplicationContext applicationContext = new
AnnotationConfigWebApplicationContext();
applicationContext.setParent(parentContext);
applicationContext.register(Child2Configuration.class);
applicationContext.refresh();
dispatcherServlet.setApplicationContext(applicationContext);
ServletRegistrationBean servletRegistrationBean = new
ServletRegistrationBean(dispatcherServlet, true, "/child2/*");
servletRegistrationBean.setName("child2");
servletRegistrationBean.setLoadOnStartup(1);
return servletRegistrationBean;
}
}