Expose a TestDispatcherServlet bean in the MockMvcAutoConfiguration

[mpryahin]

I came across an inconvenience while using @AutoConfigureMockMvc in my tests.
I have a controller that accepts multipart requests and delegates each distinct part into a Dispatcherservlet instance which is autowired into that controller - just a kind of batch endpoint implementation. Everything works great until I tried to test it via MockMvc (@AutoConfigureMockMvc).

As it turned out a MockMvc bean is created in a single isolated factory method with no interaction with the application context (a dispatcher servlet instance is created as a local variable and passed directly to MockMvc constructor instead of being looked up in the application context). This prevents my controller from being instantiated due to required been (DispatcherServlet) is not found in the application context. I've overcome this by implementing a Configuration class which creates a bean of the TestDispatcherServlet class and injects it into a MockMvc bean.
It would be great if such a behaviour is available out of the box.
Thanks in advance.

[mbhave]

I've overcome this by implementing a Configuration class which creates a bean of the TestDispatcherServlet class and injects it into a MockMvc bean.

@mpryahin Does that mean you end up with two dispatcher servlets, one that's passed directly to the MockMvc constructor and one that's created as a bean?

Could you provide a code snippet to help us understand the use-case better?

[mpryahin]

Does that mean you end up with two dispatcher servlets, one that's passed directly to the MockMvc constructor and one that's created as a bean?

No, it doesn't.

The inspiration for my use case I found here
I have a controller class that autowires a DispatcherServlet instance. The purpose of this controller is to accept batch requests each of which contains one or more self sufficient http requests (with its own headers, body, http method, url, etc...), then dispatch every sub-request via the autowired DispatcherSevlet instance, then receive responses, assemble them in a batch response and send it back to the client.

The main point to pay attention to is that my controller autowires a DispatcherServlet bean.

I tried to test my batch controller with the standard @AutoConfigureMockMvc, but failed due to no bean is exposed by the test configuration which is bootstrapped by @AutoConfigureMockMvc
You can see that MockMvc instance is created with preconfigured DispatcherServlet instance and this instance is not accessible from the spring context whatsoever.

I also saw that this servlet can be customized by customizers but it doesn't solve my main issue of not having a bean in the spring context.

After that I mimicked the test configuration class that is provided by Spring with the only one difference - I exposed the DispatcherServlet instance as a bean, something like that:

/**
 * A custom {@link MockMvc} configuration class exposes {@link DispatcherServlet} instance as a spring bean unlike the default
 * approach of creating a {@link MockMvc} instance via {@link MockMvcBuilderSupport#createMockMvc(Filter[], MockServletConfig, WebApplicationContext, RequestBuilder, List, List, List)}
 * method that inlines the {@link DispatcherServlet} instance as a method variable.
 *
 * @see org.springframework.boot.test.autoconfigure.web.servlet.MockMvcAutoConfiguration
 * @see org.springframework.test.web.servlet.MockMvcBuilderSupport
 */

@AutoConfigureWebMvc
public class MockMvcAutoConfiguration {

    @Autowired
    private WebApplicationContext webAppContext;

    @Bean
    public DispatcherServlet dispatcherServlet() throws Exception {
        WebApplicationContext wac = initWebAppContext();
        ServletContext servletContext = wac.getServletContext();
        MockServletConfig mockServletConfig = new MockServletConfig(servletContext);
        TestDispatcherServlet dispatcherServlet = new TestDispatcherServlet(wac);

        dispatcherServlet.init(mockServletConfig);
        return dispatcherServlet;
    }

    @Bean
    public MockMvc mockMvc(DispatcherServlet dispatcherServlet) {
        ServletContext servletContext = webAppContext.getServletContext();
        MockMvc mockMvc = new MockMvc((TestDispatcherServlet) dispatcherServlet, new Filter[0], servletContext);
        mockMvc.setDefaultRequest(MockMvcRequestBuilders.get("/"));
        mockMvc.setGlobalResultMatchers(Collections.emptyList());
        mockMvc.setGlobalResultHandlers(Collections.emptyList());
        return mockMvc;
    }

    private WebApplicationContext initWebAppContext() {
        ServletContext servletContext = webAppContext.getServletContext();
        ApplicationContext rootWac = WebApplicationContextUtils.getWebApplicationContext(servletContext);
        if (rootWac == null) {
            rootWac = webAppContext;
            ApplicationContext parent = webAppContext.getParent();
            while (parent != null) {
                if (parent instanceof WebApplicationContext && !(parent.getParent() instanceof WebApplicationContext)) {
                    rootWac = parent;
                    break;
                }
                parent = parent.getParent();
            }
            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, rootWac);
        }
        return webAppContext;
    }
}

It would be great if Spring exposes a DispatcherServlet instance as a bean, so that a user doesn't need to implement his own configuration as I did to solve a simillar task.

[philwebb]

@mpryahin How are you able to call new MockMvc(...) when the constructor is package private? The TestDispatcherServlet class is also package private.