通过Java类配置SpringMVC

冷不防 2022-02-18 16:58 187阅读 0赞

# 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contextConfigLocation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）