ViewResolver chain 规则

[venusdrogon]

ViewResolver chain 规则

[venusdrogon]

protected void initStrategies(ApplicationContext context) {
      ...
    initViewResolvers(context);
       ...
}

/**
     * Initialize the ViewResolvers used by this class.
     * <p>If no ViewResolver beans are defined in the BeanFactory for this
     * namespace, we default to InternalResourceViewResolver.
     */
    private void initViewResolvers(ApplicationContext context) {
        this.viewResolvers = null;

        if (this.detectAllViewResolvers) {
            // Find all ViewResolvers in the ApplicationContext, including ancestor contexts.
            Map<String, ViewResolver> matchingBeans =
                    BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.viewResolvers = new ArrayList<ViewResolver>(matchingBeans.values());
                // We keep ViewResolvers in sorted order.
                OrderComparator.sort(this.viewResolvers);
            }
        }
        else {
            try {
                ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);
                this.viewResolvers = Collections.singletonList(vr);
            }
            catch (NoSuchBeanDefinitionException ex) {
                // Ignore, we'll add a default ViewResolver later.
            }
        }

        // Ensure we have at least one ViewResolver, by registering
        // a default ViewResolver if no other resolvers are found.
        if (this.viewResolvers == null) {
            this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
            if (logger.isDebugEnabled()) {
                logger.debug("No ViewResolvers found in servlet '" + getServletName() + "': using default");
            }
        }
    }

默认

/** Detect all ViewResolvers or just expect "viewResolver" bean? */
    private boolean detectAllViewResolvers = true; 

进行查询, 默认代码

// Find all ViewResolvers in the ApplicationContext, including ancestor contexts.
Map<String, ViewResolver> matchingBeans =BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
if (!matchingBeans.isEmpty()) {
    this.viewResolvers = new ArrayList<ViewResolver>(matchingBeans.values());
    // We keep ViewResolvers in sorted order.
    OrderComparator.sort(this.viewResolvers);
}

取并排序

[venusdrogon]

在解析的时候

    /**
     * Resolve the given view name into a View object (to be rendered).
     * <p>The default implementations asks all ViewResolvers of this dispatcher.
     * Can be overridden for custom resolution strategies, potentially based on
     * specific model attributes or request parameters.
     */
    protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
            HttpServletRequest request) throws Exception {

        for (ViewResolver viewResolver : this.viewResolvers) {
            View view = viewResolver.resolveViewName(viewName, locale);
            if (view != null) {
                return view;
            }
        }
        return null;
    }

如果可以解析, 不是返回null 那么使用这个view

/**
 * Interface to be implemented by objects that can resolve views by name.
 *
 * <p>View state doesn't change during the running of the application,
 * so implementations are free to cache views.
 *
 * <p>Implementations are encouraged to support internationalization,
 * i.e. localized view resolution.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see org.springframework.web.servlet.view.InternalResourceViewResolver
 * @see org.springframework.web.servlet.view.ResourceBundleViewResolver
 * @see org.springframework.web.servlet.view.XmlViewResolver
 */
public interface ViewResolver {

    /**
     * Resolve the given view by name.
     * <p>Note: To allow for ViewResolver chaining, a ViewResolver should
     * return {@code null} if a view with the given name is not defined in it.
     * However, this is not required: Some ViewResolvers will always attempt
     * to build View objects with the given name, unable to return {@code null}
     * (rather throwing an exception when View creation failed).
     * @param viewName name of the view to resolve
     * @param locale Locale in which to resolve the view.
     * ViewResolvers that support internationalization should respect this.
     * @return the View object, or {@code null} if not found
     * (optional, to allow for ViewResolver chaining)
     * @throws Exception if the view cannot be resolved
     * (typically in case of problems creating an actual View object)
     */
    View resolveViewName(String viewName, Locale locale) throws Exception;

}

view 的情况

/**
 * MVC View for a web interaction. Implementations are responsible for rendering
 * content, and exposing the model. A single view exposes multiple model attributes.
 *
 * <p>This class and the MVC approach associated with it is discussed in Chapter 12 of
 * <a href="http://www.amazon.com/exec/obidos/tg/detail/-/0764543857/">Expert One-On-One J2EE Design and Development</a>
 * by Rod Johnson (Wrox, 2002).
 *
 * <p>View implementations may differ widely. An obvious implementation would be
 * JSP-based. Other implementations might be XSLT-based, or use an HTML generation library.
 * This interface is designed to avoid restricting the range of possible implementations.
 *
 * <p>Views should be beans. They are likely to be instantiated as beans by a ViewResolver.
 * As this interface is stateless, view implementations should be thread-safe.
 *
 * @author Rod Johnson
 * @author Arjen Poutsma
 * @see org.springframework.web.servlet.view.AbstractView
 * @see org.springframework.web.servlet.view.InternalResourceView
 */
public interface View {

    /**
     * Name of the {@link HttpServletRequest} attribute that contains the response status code.
     * <p>Note: This attribute is not required to be supported by all View implementations.
     */
    String RESPONSE_STATUS_ATTRIBUTE = View.class.getName() + ".responseStatus";

    /**
     * Name of the {@link HttpServletRequest} attribute that contains a Map with path variables.
     * The map consists of String-based URI template variable names as keys and their corresponding
     * Object-based values -- extracted from segments of the URL and type converted.
     *
     * <p>Note: This attribute is not required to be supported by all View implementations.
     */
    String PATH_VARIABLES = View.class.getName() + ".pathVariables";

    /**
     * The {@link MediaType} selected during content negotiation, which may be
     * more specific than the one the View is configured with. For example:
     * "application/vnd.example-v1+xml" vs "application/*+xml".
     */
    String SELECTED_CONTENT_TYPE = View.class.getName() + ".selectedContentType";

    /**
     * Return the content type of the view, if predetermined.
     * <p>Can be used to check the content type upfront,
     * before the actual rendering process.
     * @return the content type String (optionally including a character set),
     * or {@code null} if not predetermined.
     */
    String getContentType();

    /**
     * Render the view given the specified model.
     * <p>The first step will be preparing the request: In the JSP case,
     * this would mean setting model objects as request attributes.
     * The second step will be the actual rendering of the view,
     * for example including the JSP via a RequestDispatcher.
     * @param model Map with name Strings as keys and corresponding model
     * objects as values (Map can also be {@code null} in case of empty model)
     * @param request current HTTP request
     * @param response HTTP response we are building
     * @throws Exception if rendering failed
     */
    void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception;

}