Spring MVC 之 ContentNegotiatingViewResolver

時間 2019-12-01

標籤 spring mvc contentnegotiatingviewresolver 欄目 Spring 简体版

原文原文鏈接

咱們已經知道對於 RequestMappingInfoHandlerMapping，它在對帶有後綴的http 請求進行匹配的時候，若是找不到精確的pattern，那麼就會 pattern+.* 後再匹配 url。它會處理多個不一樣形式是 url，可是返回的只是一個view。web

ContentNegotiatingViewResolver 貌似也有這樣的功能，但其實是大不同的。ContentNegotiatingViewResolver 有些難懂，開始的時候，我也是一直沒有搞懂，反而搞暈了，很是鬱悶和尷尬。它有些複雜，但也還好。spring

如今考慮這麼一個狀況，只配置一個@RequestMapping，匹配多個 url，這些url 可能有三個方面的不一樣：json

1 其餘都相同，只是後綴不一樣。好比 /aa.jsp /aa.pdf /aa.xml /aa.json /aa （無後綴）mvc

2 其餘都相同，只是format參數不一樣。好比 /aa?view=jsp /aa?view=pdf /aa?view=xml /aa?view=json /aa(無view 參數) app

3 其餘都相同，只是accept-type不一樣。好比 /aa HTTP Request Header中的Accept 分別是 text/jsp, text/pdf, text/xml, text/json, 無Accept 請求頭yii

若是是RequestMappingInfoHandlerMapping，那麼沒法一個@RequestMapping知足這樣的要求，它須要多個@RequestMapping。jsp

ContentNegotiatingViewResolver 能夠一個@RequestMapping，返回多個view。ide

個人配置以下：測試

<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
   <property name="favorParameter" value="true"/>
   <property name="favorPathExtension" value="true"/>
   <property name="mediaTypes">
         <map>
            <entry key="xml" value="application/xml"/>   // 
            <entry key="json" value="application/json"/> // 這裏， 對於 json ，必須是application/json
            <!--<entry key="json" value="text/plain"/>-->
            <entry key="xls" value="application/vnd.ms-excel"/>
         </map>
   </property>
   <property name="viewResolvers"> 
      <list>
         <ref bean="jaxb2MarshallingXmlViewResolver"></ref>
         <ref bean="jsonViewResolver"></ref>
         <ref bean="excelViewResolver"></ref>
      </list>
   </property>
</bean>

上面的 viewResolvers 屬性是能夠不用配置的，默認spring 會查找全部 ViewResolver類型的對象。這樣，就同時支持了 parameter參數方式和後綴拓展名方式。url

這裏我直接使用了ContentNegotiatingViewResolver，實際spring 給咱們提供了 ContentNegotiationManagerFactoryBean，這是推薦的方式。配置上相似。

默認是支持path 後綴拓展方式，也支持accept 請求頭，但不支持 format 參數的。所以若是咱們想使用進行參數方式匹配，那麼咱們須要把favorParameter 設置爲true，另外此時mediaTypes 也是必須正確配置的。我感受有些不合理。應該是默認支持的，如今卻要我手動配置，不過，我測試就是這樣的結果。

源碼是：


private boolean favorPathExtension = true; // 支持

private boolean favorParameter = false; // 默認不支持

private boolean ignoreAcceptHeader = false; // 默認支持accept頭 

private Map<String, MediaType> mediaTypes = new HashMap<String, MediaType>();

private boolean ignoreUnknownPathExtensions = true;

private Boolean useJaf;

private String parameterName = "format";

除了xml 方式配置，咱們可使用註解方式配置：

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.yiibai.springmvc")
public class AppConfig extends WebMvcConfigurerAdapter {

    /*
     * Configure ContentNegotiationManager
     */
    @Override
    public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
        configurer.ignoreAcceptHeader(true).defaultContentType(
                MediaType.TEXT_HTML);
    }

    /*
     * Configure ContentNegotiatingViewResolver
     */
    @Bean
    public ViewResolver contentNegotiatingViewResolver(ContentNegotiationManager manager) {
        ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
        resolver.setContentNegotiationManager(manager);

        // Define all possible view resolvers
        List<ViewResolver> resolvers = new ArrayList<ViewResolver>();

        resolvers.add(jaxb2MarshallingXmlViewResolver());
        resolvers.add(jsonViewResolver());
        resolvers.add(jspViewResolver());
        resolvers.add(pdfViewResolver());
        resolvers.add(excelViewResolver());
        
        resolver.setViewResolvers(resolvers);
        return resolver;
    }

    /*
     * Configure View resolver to provide XML output Uses JAXB2 marshaller to
     * marshall/unmarshall POJO's (with JAXB annotations) to XML
     */
    @Bean
    public ViewResolver jaxb2MarshallingXmlViewResolver() {
        Jaxb2Marshaller marshaller = new Jaxb2Marshaller();
        marshaller.setClassesToBeBound(Pizza.class);
        return new Jaxb2MarshallingXmlViewResolver(marshaller);
    }

    /*
     * Configure View resolver to provide JSON output using JACKSON library to
     * convert object in JSON format.
     */
    @Bean
    public ViewResolver jsonViewResolver() {
        return new JsonViewResolver();
    }

    /*
     * Configure View resolver to provide PDF output using lowagie pdf library to
     * generate PDF output for an object content
     */
    @Bean
    public ViewResolver pdfViewResolver() {
        return new PdfViewResolver();
    }

    /*
     * Configure View resolver to provide XLS output using Apache POI library to
     * generate XLS output for an object content
     */
    @Bean
    public ViewResolver excelViewResolver() {
        return new ExcelViewResolver();
    }

    /*
     * Configure View resolver to provide HTML output This is the default format
     * in absence of any type suffix.
     */
    @Bean
    public ViewResolver jspViewResolver() {
        InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
        viewResolver.setViewClass(JstlView.class);
        viewResolver.setPrefix("/WEB-INF/views/");
        viewResolver.setSuffix(".jsp");
        return viewResolver;
    }

}

對於boot，其自動配置了一個

        @Bean
        @ConditionalOnBean({ViewResolver.class})
        @ConditionalOnMissingBean(
            name = {"viewResolver"},
            value = {ContentNegotiatingViewResolver.class}
        )
        public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {
            ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
            resolver.setContentNegotiationManager((ContentNegotiationManager)beanFactory.getBean(ContentNegotiationManager.class));
            resolver.setOrder(-2147483648);
            return resolver;
        }


        @Bean
        public ContentNegotiationManager mvcContentNegotiationManager() {
            ContentNegotiationManager manager = super.mvcContentNegotiationManager();
            List<ContentNegotiationStrategy> strategies = manager.getStrategies();
            ListIterator iterator = strategies.listIterator();

            while(iterator.hasNext()) {
                ContentNegotiationStrategy strategy = (ContentNegotiationStrategy)iterator.next();
                if (strategy instanceof PathExtensionContentNegotiationStrategy) { // 只支持後綴 方式匹配
                    iterator.set(new WebMvcAutoConfiguration.OptionalPathExtensionContentNegotiationStrategy(strategy)); 
                }
            }

            return manager;
        }