JSF 请求之恢复视图(Restore View phase) 阶段

深碍√TFBOYSˉ_ 2022-05-15 14:45 114阅读 0赞

JSF 除了事件处理之外，总共必须经过六个阶段：

1、恢复视图阶段 Restore View Phase

2、应用请求值阶段 Apply Request Value Phase

3、验证阶段 Process Validation Phase

4、更新模型值阶段 Update Model Values Phase

5、调用应用程序阶段 Invoke Application Phase

6、渲染阶段 Render Response Phase

这六个阶段分别对应六个执行器 RestoreViewExecutor，ApplyRequestValuesExecutor，ProcessValidationsExecutor， UpdateModelValuesExecutor，InvokeApplicationExecutor，RenderResponseExecutor，且都与生命周期对象（LifecycleImpl）耦合。

在此，主要先说下第一阶段，恢复视图阶段 Restore View Phase主要做了什么，起了什么作用？

在项目中引入JSF的是javax.faces.webapp.FacesServlet类,其关联了javax.faces.lifecycle.Lifecycle,所以在JSF中生命周期的

概念是非常重要的，一直贯穿一个请求的始终。而在LIfecycle的实现类LifecycleImpl中又关联了PhaseExecutor类（是一个数组）,包括： RestoreViewExecutor、ApplyRequestValuesExecutor、ProcessValidationsExecutor、 UpdateModelValuesExecutor、 InvokeApplicationExecutor、RenderResponseExecutor,这六个类共同继承了PhaseExecutor。其中RenderResponseExecutor是作一个单独的属性进行关联的。

接下来我们来先看一段RestoreViewExecutor类中的核心代码:

public boolean execute(FacesContext facesContext)
        {
            if (facesContext == null)
            {
                throw new FacesException("FacesContext is null");
            }
    
            // get some required Objects
            Application application = facesContext.getApplication();
            ViewHandler viewHandler = application.getViewHandler();
            UIViewRoot viewRoot = facesContext.getViewRoot();
            RestoreViewSupport restoreViewSupport = getRestoreViewSupport(facesContext);
    
            // Examine the FacesContext instance for the current request. If it already contains a UIViewRoot
            if (viewRoot != null)
            {
                if (log.isLoggable(Level.FINEST))
                {
                    log.finest("View already exists in the FacesContext");
                }
                
                // Set the locale on this UIViewRoot to the value returned by the getRequestLocale() method on the
                // ExternalContext for this request
                viewRoot.setLocale(facesContext.getExternalContext().getRequestLocale());
                
                restoreViewSupport.processComponentBinding(facesContext, viewRoot);
                
                // invoke the afterPhase MethodExpression of UIViewRoot
                _invokeViewRootAfterPhaseListener(facesContext);
                
                return false;
            }
    .......

首先在JSF上下文中寻找组件树（UIViewRoot），如果找到则说明视图已经存在于上下文中，这时主要做了以下几件事：

1)、把当前请求的Lacale赋给组件树。

2)、执行组件树与EL表达式的绑定。？

在这里RestoreViewExecutor关联了RestoreViewSupport类，调用了该类的一个方法：processComponentBinding

这个方法的主要作用是：

在这个方法里依赖了component这个类，循环调用了这个类的visitTree(visitContext, new RestoreStateCallback());

3)、 // invoke the afterPhase MethodExpression of UIViewRoot  
                    \_invokeViewRootAfterPhaseListener(facesContext); ？

如果找不到呢，接着来看这段代码：

String viewId = restoreViewSupport.calculateViewId(facesContext);
    
            // Determine if the current request is an attempt by the 
            // servlet container to display an error page.
            // If the request is an error page request, the servlet container
            // is required to set the request parameter "javax.servlet.error.message".
            final boolean errorPageRequest = facesContext.getExternalContext().getRequestMap()
                                                     .get("javax.servlet.error.message") != null;
            
            // Determine if this request is a postback or an initial request.
            // But if it is an error page request, do not treat it as a postback (since 2.0)
            if (!errorPageRequest && restoreViewSupport.isPostback(facesContext))
            { // If the request is a postback
                if (log.isLoggable(Level.FINEST))
                {
                    log.finest("Request is a postback");
                }
    
                try
                {
                    facesContext.setProcessingEvents(false);
                    // call ViewHandler.restoreView(), passing the FacesContext instance for the current request and the 
                    // view identifier, and returning a UIViewRoot for the restored view.
                    viewRoot = viewHandler.restoreView(facesContext, viewId);
                    if (viewRoot == null)
                    {
                        // If the return from ViewHandler.restoreView() is null, throw a ViewExpiredException with an 
                        // appropriate error message.
                        throw new ViewExpiredException("No saved view state could be found for the view identifier: "
                                                       + viewId, viewId);
                    }
                    
                    // Store the restored UIViewRoot in the FacesContext.
                    facesContext.setViewRoot(viewRoot);
                }
                finally
                {
                    facesContext.setProcessingEvents(true);
                }
                
                // Restore binding
                // See https://javaserverfaces-spec-public.dev.java.net/issues/show_bug.cgi?id=806
                restoreViewSupport.processComponentBinding(facesContext, viewRoot);
            }
            else
            { // If the request is a non-postback
                if (log.isLoggable(Level.FINEST))
                {
                    log.finest("Request is not a postback. New UIViewRoot will be created");
                }
                
                //viewHandler.deriveViewId(facesContext, viewId)
                //restoreViewSupport.deriveViewId(facesContext, viewId)
                ViewDeclarationLanguage vdl = viewHandler.getViewDeclarationLanguage(facesContext, 
                        viewHandler.deriveLogicalViewId(facesContext, viewId));
                
                // viewHandler.deriveLogicalViewId() could trigger an InvalidViewIdException, which
                // it is handled internally sending a 404 error code set the response as complete.
                if (facesContext.getResponseComplete())
                {
                    return true;
                }
                
                if (vdl != null)
                {
                    ViewMetadata metadata = vdl.getViewMetadata(facesContext, viewId);
                    
                    Collection<UIViewParameter> viewParameters = null;
                    
                    if (metadata != null)
                    {
                        viewRoot = metadata.createMetadataView(facesContext);
                        
                        if (viewRoot != null)
                        {
                            viewParameters = ViewMetadata.getViewParameters(viewRoot);
                        }
                        else if(facesContext.getResponseComplete())
                        {
                            // this can happen if the current request is a debug request,
                            // in this case no further processing is necessary
                            return true;
                        }
                    }
        
                    // If viewParameters is not an empty collection DO NOT call renderResponse
                    if ( !(viewParameters != null && !viewParameters.isEmpty()) )
                    {
                        // Call renderResponse() on the FacesContext.
                        facesContext.renderResponse();
                    }
                }
                else
                {
                    // Call renderResponse
                    facesContext.renderResponse();
                }
                
                // viewRoot can be null here, if ...
                //   - we don't have a ViewDeclarationLanguage (e.g. when using facelets-1.x)
                //   - there is no view metadata or metadata.createMetadataView() returned null
                if (viewRoot == null)
                {
                    // call ViewHandler.createView(), passing the FacesContext instance for the current request and 
                    // the view identifier
                    viewRoot = viewHandler.createView(facesContext, viewId);
                }
                
                // Subscribe the newly created UIViewRoot instance to the AfterAddToParent event, passing the 
                // UIViewRoot instance itself as the listener.
                // -= Leonardo Uribe =- This line it is not necessary because it was
                // removed from jsf 2.0 section 2.2.1 when pass from EDR2 to Public Review 
                // viewRoot.subscribeToEvent(PostAddToViewEvent.class, viewRoot);
                
                // Store the new UIViewRoot instance in the FacesContext.
                facesContext.setViewRoot(viewRoot);
                
                // Publish an AfterAddToParent event with the created UIViewRoot as the event source.
                application.publishEvent(facesContext, PostAddToViewEvent.class, viewRoot);
            }
    
            // add the ErrorPageBean to the view map to fully support 
            // facelet error pages, if we are in ProjectStage Development
            // and currently generating an error page
            if (errorPageRequest && facesContext.isProjectStage(ProjectStage.Development))
            {
                facesContext.getViewRoot().getViewMap()
                        .put(ErrorPageWriter.ERROR_PAGE_BEAN_KEY, new ErrorPageWriter.ErrorPageBean());
            }
            
            // invoke the afterPhase MethodExpression of UIViewRoot
            _invokeViewRootAfterPhaseListener(facesContext);
            
            return false;
        }

1、置ViewId

2、判断是否是个错误页面请求

3、如果这不是一个错误页面请求且是一个回传请求或者初始请求，

那就找出viewRoot并把它设置到facesContext？（viewHandler.restoreView(facesContext, viewId);）

4、如果这不是一个回传请求：

这边依赖于ViewHandler类生成了ViewDeclarationLanguage视图描述语言实例,

如果这个实例不为空，则：用这个实例取得视图元数据

ViewMetadata metadata = vdl.getViewMetadata(facesContext, viewId);

再用视图元数据创建ViewRoot

还用视图元数据取得视图参数viewParameter，如果有直接进入渲染环节

如果这个视图描述语言实例为空，直接进入渲染环节。

如果到这边viewRoot还是为空，则用viewHandler生成视图根目录。

viewRoot = viewHandler.createView(facesContext, viewId);（e.g. when using facelets-1.x）

否则，把viewRoot设置到FacesContext中，

Publish an AfterAddToParent event with the created UIViewRoot as the event source.

// invoke the afterPhase MethodExpression of UIViewRoot

FacesContext可以看做是一个RequestWrapper（注意这个FaceContext和ServletContext不一样，ServletContext是一个Web应用只有一个的全局对象，对应的是一个Web application，而一个FacesContext对应的是一个request，另外，RequestWrapper这个说法不严格，实际上FacesContext里面也包装了ServletContext、Response等）。而LifeCycle可以看做是一个过滤器链（类似于servlet规范里面的Filter Chain）。于是，整个JSF请求处理过程，实际上就是包装成为FaceContext的用户请求，通过类似于一个Filter Chain的LifeCycle的过程。