Why does Spring MVC respond with a 404 and report quot;No mapping found for HTTP request with URI [...] in DispatcherServletquot;?(为什么 Spring MVC 以 404 响应并报告“No mapping found for HTTP request with URI [...] in DispatcherServlet?)

问题描述

I'm writing a Spring MVC application deployed on Tomcat. See the following minimal, complete, and verifiable example

public class Application extends AbstractAnnotationConfigDispatcherServletInitializer {
    protected Class<?>[] getRootConfigClasses() {
        return new Class<?>[] { };
    }
    protected Class<?>[] getServletConfigClasses() {
        return new Class<?>[] { SpringServletConfig.class };
    }
    protected String[] getServletMappings() {
        return new String[] { "/*" };
    }
}

Where SpringServletConfig is

@Configuration
@ComponentScan("com.example.controllers")
@EnableWebMvc
public class SpringServletConfig {
    @Bean
    public InternalResourceViewResolver resolver() {
        InternalResourceViewResolver vr = new InternalResourceViewResolver();
        vr.setPrefix("/WEB-INF/jsps/");
        vr.setSuffix(".jsp");
        return vr;
    }
}

Finally, I have a @Controller in the package com.example.controllers

@Controller
public class ExampleController {
    @RequestMapping(path = "/home", method = RequestMethod.GET)
    public String example() {
        return "index";
    }
}

My application's context name is Example. When I send a request to

http://localhost:8080/Example/home

the application responds with an HTTP Status 404 and logs the following

WARN  o.s.web.servlet.PageNotFound - No mapping found for HTTP request with URI `[/Example/WEB-INF/jsps/index.jsp]` in `DispatcherServlet` with name 'dispatcher'

I have a JSP resource at /WEB-INF/jsps/index.jsp I expected Spring MVC to use my controller to handle the request and forward to the JSP, so why is it responding with a 404?

This is meant to be a canonical post for questions about this warning message.

Your standard Spring MVC application will serve all requests through a DispatcherServlet that you've registered with your Servlet container.

The DispatcherServlet looks at its ApplicationContext and, if available, the ApplicationContext registered with a ContextLoaderListener for special beans it needs to setup its request serving logic. These beans are described in the documentation.

Arguably the most important, beans of type HandlerMapping map

incoming requests to handlers and a list of pre- and post-processors (handler interceptors) based on some criteria the details of which vary by HandlerMapping implementation. The most popular implementation supports annotated controllers but other implementations exists as well.

The javadoc of HandlerMapping further describes how implementations must behave.

The DispatcherServlet finds all beans of this type and registers them in some order (can be customized). While serving a request, the DispatcherServlet loops through these HandlerMapping objects and tests each of them with getHandler to find one that can handle the incoming request, represented as the standard HttpServletRequest. As of 4.3.x, if it doesn't find any, it logs the warning that you see

No mapping found for HTTP request with URI [/some/path] in DispatcherServlet with name SomeName

and either throws a NoHandlerFoundException or immediately commits the response with a 404 Not Found status code.

Why didn't the DispatcherServlet find a HandlerMapping that could handle my request?

The most common HandlerMapping implementation is RequestMappingHandlerMapping, which handles registering @Controller beans as handlers (really their @RequestMapping annotated methods). You can either declare a bean of this type yourself (with @Bean or <bean> or other mechanism) or you can use the built-in options. These are:

1. Annotate your @Configuration class with @EnableWebMvc.
2. Declare a <mvc:annotation-driven /> member in your XML configuration.

As the link above describes, both of these will register a RequestMappingHandlerMapping bean (and a bunch of other stuff). However, a HandlerMapping isn't very useful without a handler. RequestMappingHandlerMapping expects some @Controller beans so you need to declare those too, through @Bean methods in a Java configuration or <bean> declarations in an XML configuration or through component scanning of @Controller annotated classes in either. Make sure these beans are present.

If you're getting the warning message and a 404 and you've configured all of the above correctly, then you're sending your request to the wrong URI, one that isn't handled by a detected @RequestMapping annotated handler method.

The spring-webmvc library offers other built-in HandlerMapping implementations. For example, BeanNameUrlHandlerMapping maps

from URLs to beans with names that start with a slash ("/")

and you can always write your own. Obviously, you'll have to make sure the request you're sending matches at least one of the registered HandlerMapping object's handlers.

If you don't implicitly or explicitly register any HandlerMapping beans (or if detectAllHandlerMappings is true), the DispatcherServlet registers some defaults. These are defined in DispatcherServlet.properties in the same package as the DispatcherServlet class. They are BeanNameUrlHandlerMapping and DefaultAnnotationHandlerMapping (which is similar to RequestMappingHandlerMapping but deprecated).

Debugging

Spring MVC will log handlers registered through RequestMappingHandlerMapping. For example, a @Controller like

@Controller
public class ExampleController {
    @RequestMapping(path = "/example", method = RequestMethod.GET, headers = "X-Custom")
    public String example() {
        return "example-view-name";
    }
}

will log the following at INFO level

Mapped "{[/example],methods=[GET],headers=[X-Custom]}" onto public java.lang.String com.spring.servlet.ExampleController.example()

This describes the mapping registered. When you see the warning that no handler was found, compare the URI in the message to the mapping listed here. All the restrictions specified in the @RequestMapping must match for Spring MVC to select the handler.

Other HandlerMapping implementations log their own statements that should hint to their mappings and their corresponding handlers.

Similarly, enable Spring logging at DEBUG level to see which beans Spring registers. It should report which annotated classes it finds, which packages it scans, and which beans it initializes. If the ones you expected aren't present, then review your ApplicationContext configuration.

Other common mistakes

A DispatcherServlet is just a typical Java EE Servlet. You register it with your typical <web.xml> <servlet-class> and <servlet-mapping> declaration, or directly through ServletContext#addServlet in a WebApplicationInitializer, or with whatever mechanism Spring boot uses. As such, you must rely on the url mapping logic specified in the Servlet specification, see Chapter 12. See also

• How are Servlet url mappings in web.xml used?

With that in mind, a common mistake is to register the DispatcherServlet with a url mapping of /*, returning a view name from a @RequestMapping handler method, and expecting a JSP to be rendered. For example, consider a handler method like

@RequestMapping(path = "/example", method = RequestMethod.GET)
public String example() {
    return "example-view-name";
}

with an InternalResourceViewResolver

@Bean
public InternalResourceViewResolver resolver() {
    InternalResourceViewResolver vr = new InternalResourceViewResolver();
    vr.setPrefix("/WEB-INF/jsps/");
    vr.setSuffix(".jsp");
    return vr;
}

you might expect the request to be forwarded to a JSP resource at the path /WEB-INF/jsps/example-view-name.jsp. This won't happen. Instead, assuming a context name of Example, the DisaptcherServlet will report

No mapping found for HTTP request with URI [/Example/WEB-INF/jsps/example-view-name.jsp] in DispatcherServlet with name 'dispatcher'

Because the DispatcherServlet is mapped to /* and /* matches everything (except exact matches, which have higher priority), the DispatcherServlet would be chosen to handle the forward from the JstlView (returned by the InternalResourceViewResolver). In almost every case, the DispatcherServlet will not be configured to handle such a request.

Instead, in this simplistic case, you should register the DispatcherServlet to /, marking it as the default servlet. The default servlet is the last match for a request. This will allow your typical servlet container to chose an internal Servlet implementation, mapped to *.jsp, to handle the JSP resource (for example, Tomcat has JspServlet), before trying with the default servlet.

That's what you're seeing in your example.

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