【小家Spring】Spring MVC容器的web九大组件之---ViewResolver源码详解---视图解析器ViewResolver详解（下）

// 模板视图解析程序的抽象基类，尤其是FreeMarker视图的抽象基类
// @since 1.1  对应的View是AbstractTemplateView
public class AbstractTemplateViewResolver extends UrlBasedViewResolver {
  // 是否吧所有热request里面的attributes都加入合并到模版的Model，默认是false
  private boolean exposeRequestAttributes = false;
  // 是否允许request里面的属性，当name相同的时候，复写model里面的 默认是false
  private boolean allowRequestOverride = false;
  // session相关，语义同上
  private boolean exposeSessionAttributes = false;
  private boolean allowSessionOverride = false;
  // Set whether to expose a RequestContext for use by Spring's macro library 默认值是true
  private boolean exposeSpringMacroHelpers = true;
  // 它只会处理AbstractTemplateView 比如FreeMarkerView是它的实现类
  @Override
  protected Class<?> requiredViewClass() {
    return AbstractTemplateView.class;
  }
  // 模版操作：其实就是多设置了一些开关属性~~~~
  @Override
  protected AbstractUrlBasedView buildView(String viewName) throws Exception {
    AbstractTemplateView view = (AbstractTemplateView) super.buildView(viewName);
    view.setExposeRequestAttributes(this.exposeRequestAttributes);
    view.setAllowRequestOverride(this.allowRequestOverride);
    view.setExposeSessionAttributes(this.exposeSessionAttributes);
    view.setAllowSessionOverride(this.allowSessionOverride);
    view.setExposeSpringMacroHelpers(this.exposeSpringMacroHelpers);
    return view;
  }
}

  @Override
  protected Class<?> requiredViewClass() {
    return FreeMarkerView.class;
  }

public class BeanNameViewResolver extends WebApplicationObjectSupport implements ViewResolver, Ordered {
  // 默认排序最小值~~~
  private int order = Ordered.LOWEST_PRECEDENCE;  // default: same as non-Ordered
  public void setOrder(int order) {
    this.order = order;
  }
  @Override
  public int getOrder() {
    return this.order;
  }
  @Override
  @Nullable
  public View resolveViewName(String viewName, Locale locale) throws BeansException {
    // 可见它和容器强关联，若容器里没有这个Bean，他就直接返回null了~~~
    ApplicationContext context = obtainApplicationContext();
    if (!context.containsBean(viewName)) {
      // Allow for ViewResolver chaining...
      return null;
    }
    // 可见不仅仅要含有此Bean，还必须是view类型的~~~~  否则也是返回null
    if (!context.isTypeMatch(viewName, View.class)) {
      if (logger.isDebugEnabled()) {
        logger.debug("Found bean named '" + viewName + "' but it does not implement View");
      }
      return null;
    }
    // 拿出这个View就这直接返回了~~~
    return context.getBean(viewName, View.class);
  }
}

// @since 4.1
public class ViewResolverComposite implements ViewResolver, Ordered, InitializingBean, ApplicationContextAware, ServletContextAware {
  private final List<ViewResolver> viewResolvers = new ArrayList<>();
  private int order = Ordered.LOWEST_PRECEDENCE;
  // 若直接set了，就以自己的set为主
  public void setViewResolvers(List<ViewResolver> viewResolvers) {
    this.viewResolvers.clear();
    if (!CollectionUtils.isEmpty(viewResolvers)) {
      this.viewResolvers.addAll(viewResolvers);
    }
  }
  // 为每一个实现了接口ApplicationContextAware的 都设置一个 下面还有其它的
  @Override
  public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
    for (ViewResolver viewResolver : this.viewResolvers) {
      if (viewResolver instanceof ApplicationContextAware) {
        ((ApplicationContextAware)viewResolver).setApplicationContext(applicationContext);
      }
    }
  }
  ...
  // 这是核心   遍历所有的viewResolvers,第一个不返回null的，就标出处理了~~~~
  @Override
  @Nullable
  public View resolveViewName(String viewName, Locale locale) throws Exception {
    for (ViewResolver viewResolver : this.viewResolvers) {
      View view = viewResolver.resolveViewName(viewName, locale);
      if (view != null) {
        return view;
      }
    }
    return null;
  }
}

@Component
public class HelloView implements View {
    @Override
    public String getContentType() {
        return MediaType.TEXT_HTML_VALUE;
    }
    // 这里渲染，就向控制台写一句话即可~~~~
    @Override
    public void render(Map<String, ?> model, HttpServletRequest request,
                       HttpServletResponse response) throws Exception {
        response.getWriter().print("Welcome to View:" + new Date());
    }
}
@Controller  
public class MyView {  
    @RequestMapping(value="/testBeanNameViewResolver")  
    public String testView(){  
        System.out.println("testBeanNameViewResolver");  
        return "helloView";
    }  
}
// 把BeanNameViewResolver 配置进容器
@Configuration
@EnableWebMvc
public class WebMvcConfig extends WebMvcConfigurerAdapter {
    @Override
    public void configureViewResolvers(ViewResolverRegistry registry) {
        BeanNameViewResolver viewResolver = new BeanNameViewResolver();
        viewResolver.setOrder(10); // 这样能保证在InternalResourceViewResolver之前执行
        registry.viewResolver(viewResolver);
    }
    // 这是错误的注册方式~~~会让ViewResolverComposite可能失效~~
    //@Bean
    //public ViewResolver viewResolver() {
    //    BeanNameViewResolver viewResolver = new BeanNameViewResolver();
    //    viewResolver.setOrder(10); // 这样能保证在InternalResourceViewResolver之前执行
    //    return viewResolver;
    //}