SpringMVC配置以Java类配置

如果在使用SpringMVC时不希望采用XML的配置方式，而采用基于Java类的配置也是可以的。如果还希望在web.xml中配置DispatcherServlet，则需要通过init-param指定contextClass为AnnotationConfigWebApplicationContext，然后把context ConfigLocation指定为SpringMVC配置Java类的全路径名称。

<servlet>
    <servlet-name>spring</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextClass</param-name>
        <param-value>org.springframework.web.context.support.AnnotationConfigWebApplicationContext</param-value>
    </init-param>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>com.elim.spring.mvc.MvcConfiguration</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>spring</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>

在Java配置类中就可以按照正常的Java类配置那样定义，如下则定义了扫描com.elim.spring.mvc.controller包下面的Class。

@ComponentScan(basePackages = "com.elim.spring.mvc.controller")
public class MvcConfiguration {

}

如果定义DispatcherServlet时还是指定的配置文件为XML文件，则也可以在对应的XML配置文件中定义上面的Java配置类为一个bean，效果是一样的。

之后可以在该配置类中定义一些SpringMVC配置bean，比如下面就定义了一个InternalResourceViewResolver。

@ComponentScan(basePackages = "com.elim.spring.mvc.controller")
public class MvcConfiguration {

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

}

WebMvcConfigurer

在进行配置时也可以选择实现WebMvcConfigurer接口进行配置，或者选择继承自抽象类WebMvcConfigurerAdapter，然后重写感兴趣的方法。以下是WebMvcConfigurer的定义。

public interface WebMvcConfigurer {

	/**
	 * Add {@link Converter}s and {@link Formatter}s in addition to the ones
	 * registered by default.
	 */
	void addFormatters(FormatterRegistry registry);

	/**
	 * Configure the {@link HttpMessageConverter}s to use in argument resolvers
	 * and return value handlers that support reading and/or writing to the
	 * body of the request and response. If no message converters are added to
	 * the list, default converters are added instead.
	 * @param converters initially an empty list of converters
	 */
	void configureMessageConverters(List<HttpMessageConverter<?>> converters);

	/**
	 * Provide a custom {@link Validator} instead of the one created by default.
	 * The default implementation, assuming JSR-303 is on the classpath, is:
	 * {@link org.springframework.validation.beanvalidation.OptionalValidatorFactoryBean}.
	 * Leave the return value as {@code null} to keep the default.
	 */
	Validator getValidator();

	/**
	 * Configure content negotiation options.
	 */
	void configureContentNegotiation(ContentNegotiationConfigurer configurer);

	/**
	 * Configure asynchronous request handling options.
	 */
	void configureAsyncSupport(AsyncSupportConfigurer configurer);

	/**
	 * Helps with configuring HandlerMappings path matching options such as trailing slash match,
	 * suffix registration, path matcher and path helper.
	 * Configured path matcher and path helper instances are shared for:
	 * <ul>
	 *     <li>RequestMappings</li>
	 *     <li>ViewControllerMappings</li>
	 *     <li>ResourcesMappings</li>
	 * </ul>
	 * @since 4.0.3
	 */
	void configurePathMatch(PathMatchConfigurer configurer);

	/**
	 * Add resolvers to support custom controller method argument types.
	 * <p>This does not override the built-in support for resolving handler
	 * method arguments. To customize the built-in support for argument
	 * resolution, configure {@link RequestMappingHandlerAdapter} directly.
	 * @param argumentResolvers initially an empty list
	 */
	void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers);

	/**
	 * Add handlers to support custom controller method return value types.
	 * <p>Using this option does not override the built-in support for handling
	 * return values. To customize the built-in support for handling return
	 * values, configure RequestMappingHandlerAdapter directly.
	 * @param returnValueHandlers initially an empty list
	 */
	void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers);

	/**
	 * Configure the {@link HandlerExceptionResolver}s to handle unresolved
	 * controller exceptions. If no resolvers are added to the list, default
	 * exception resolvers are added instead.
	 * @param exceptionResolvers initially an empty list
	 */
	void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers);

	/**
	 * Add Spring MVC lifecycle interceptors for pre- and post-processing of
	 * controller method invocations. Interceptors can be registered to apply
	 * to all requests or be limited to a subset of URL patterns.
	 */
	void addInterceptors(InterceptorRegistry registry);

	/**
	 * Provide a custom {@link MessageCodesResolver} for building message codes
	 * from data binding and validation error codes. Leave the return value as
	 * {@code null} to keep the default.
	 */
	MessageCodesResolver getMessageCodesResolver();

	/**
	 * Configure simple automated controllers pre-configured with the response
	 * status code and/or a view to render the response body. This is useful in
	 * cases where there is no need for custom controller logic -- e.g. render a
	 * home page, perform simple site URL redirects, return a 404 status with
	 * HTML content, a 204 with no content, and more.
	 */
	void addViewControllers(ViewControllerRegistry registry);

	/**
	 * Configure view resolvers to translate String-based view names returned from
	 * controllers into concrete {@link org.springframework.web.servlet.View}
	 * implementations to perform rendering with.
	 */
	void configureViewResolvers(ViewResolverRegistry registry);

	/**
	 * Add handlers to serve static resources such as images, js, and, css
	 * files from specific locations under web application root, the classpath,
	 * and others.
	 */
	void addResourceHandlers(ResourceHandlerRegistry registry);

	/**
	 * Configure a handler to delegate unhandled requests by forwarding to the
	 * Servlet container's "default" servlet. A common use case for this is when
	 * the {@link DispatcherServlet} is mapped to "/" thus overriding the
	 * Servlet container's default handling of static resources.
	 */
	void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer);

}

采用继承WebMvcConfigurerAdapter的方式，上面的配置可以改写为如下这样。

@ComponentScan(basePackages = "com.elim.spring.mvc.controller")
public class MvcConfiguration  extends WebMvcConfigurerAdapter  {

	@Override
	public void configureViewResolvers(ViewResolverRegistry registry) {
		registry.jsp("/WEB-INF/view/", ".jsp");
	}

}

@EnableWebMvc

在使用Java配置时也可以在配置类上使用@EnableWebMvc，这样SpringMVC将进行一些自动配置。具体的自动配置内容可以参考WebMvcConfigurationSupport类的定义。当然也可以选择直接继承自WebMvcConfigurationSupport，然后进行部分方法重写。

@EnableWebMvc
@ComponentScan(basePackages = "com.elim.learn.spring.mvc.controller")
public class MvcConfiguration  extends WebMvcConfigurerAdapter  {

	@Override
	public void configureViewResolvers(ViewResolverRegistry registry) {
		registry.jsp("/WEB-INF/view/", ".jsp");
	}

	@Override
	public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
		converters.add(new MappingJackson2HttpMessageConverter());
		converters.add(new StringHttpMessageConverter(Charset.defaultCharset()));
	}

}

AbstractAnnotationConfigDispatcherServletInitializer

如果希望不在web.xml文件中定义DispatcherServlet，而是完全通过程序来定义，可以选择定义一个AbstractDispatcherServletInitializer的子类，然后实现其中的抽象方法。如果是需要使用基于注解的配置，则可以直接继承AbstractAnnotationConfigDispatcherServletInitializer类。AbstractAnnotationConfigDispatcherServletInitializer中定义了三个抽象方法，getRootConfigClasses()用来定义根配置的类，即对应根ApplicationContext的配置类，如果这个配置还是通过在web.xml中配置的则可以忽略它；getServletConfigClasses()则对应SpringMVC配置的配置类；getServletMappings()则用于指定需要映射的地址。以下就是自定义的一个初始化类，它会在容器启动的时候自动发现，然后进行SpringMVC的初始化工作。

public class SpringInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

	@Override
	protected Class<?>[] getRootConfigClasses() {
		return null;
	}

	@Override
	protected Class<?>[] getServletConfigClasses() {
		return new Class<?>[]{MvcConfiguration.class};
	}

	@Override
	protected String[] getServletMappings() {
		return new String[]{"/"};
	}

}

（注：本文是基于Spring4.1.0所写）