How to get the DispatcherServlet from spring WebApplicationContext? - spring-boot

Question

How to get the DispatcherServlet instance from a spring WebApplicationContext object?
I want to perform a direct request to the the front controller servlet (avoiding the network interface) and check the response from a spring application, e.g. WebApplicationContext instance.
Notice, we are not able to use MockMvc to check the HTML rendered by JSP because: "if you use JSPs, you can verify the JSP page to which the request was forwarded, but no HTML is rendered"(according to MockMvc vs End-to-End Tests)
So maybe if we get the DispatcherServlet instance we could perform the request through its doDispatch method and check the content from response.

Answer 1

When you look at
DispatcherServlet.java, there is a constructor with WebApplicationContext as parameter, but the super constructor from FrameworkServlet.java does only hold the field itself, without any callbacks - so the given web application context will not know the dispatcher servlet.
So I don't think you can resolve the dispatcher servlet by the WebApplicationContext. Of course you could try to inject/autowire the DispatcherServlet - maybe this is also possible inside tests, but I am not sure.
I think the most easiest way to check for JSP outputs would be to test those parts with a real server as described at Testing with a running server . This should give you the complete output and web application behaviour inside your test without any workarounds.

Answer 2

Dispatcher Servlet : It acts as front controller for Spring based web applications. It provides a mechanism for request processing where actual work is performed by configurable, delegate components. It is inherited from HttpServlet, HttpServletBean and FrameworkServlet. It also implements ApplicationContextAware hence it is able to set ApplicationContext.
WebApplicationContext : It is an extension of a plain ApplicationContext. It is web aware ApplicationContext i.e it has Servlet Context information. When DispatcherServlet is loaded, it looks for the bean configuration file of WebApplicationContext and initializes it.
So you can set and get the instance of any ApplicationContext from DispatcherServlet but not vice-versa.
dispatcherServlet.getWebApplicationContext();
Although, you can get an instance of DispatcherServlet but I doubt it will serve your purpose as it's scope is protected.
#Autowired
DispatcherServlet dispatcherServlet;
Code inside DispatcherServlet
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
It is possible to create your own DispatcherServlet and perform actions. You can override the default one created by Spring boot app.
Sample:
public class SampleDispatcherServlet extends DispatcherServlet {
private final Log logger = LogFactory.getLog(getClass());
#Override
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
// You can use other implementations of HttpServletRequest and
// HttpServletResponse as per your requirement
// e.g. FormContentRequestWrapper , ResourceUrlEncodingResponseWrapper many more
if (!(request instanceof ContentCachingRequestWrapper)) {
request = new ContentCachingRequestWrapper(request);
}
if (!(response instanceof ContentCachingResponseWrapper)) {
response = new ContentCachingResponseWrapper(response);
}
HandlerExecutionChain handler = getHandler(request);
try {
// Any task to be done
super.doDispatch(request, response);
} finally {
// Some task to be done
}
}
}
HandlerExecutionChain- Handler mapper is used to match current request to appropriated controller. Interceptors are the objects invoked before and after some of dispatching actions
Then we have to register the DispatcherServlet:
#Bean
public ServletRegistrationBean dispatcherRegistration() {
return new ServletRegistrationBean(dispatcherServlet());
}
//The bean name for a DispatcherServlet that will be mapped to the root URL "/"
#Bean(name = DispatcherServletAutoConfiguration.DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServlet dispatcherServlet() {
return new SampleDispatcherServlet();
}