springMVC源码分析--FlashMap和FlashMapManager重定向数据保存

Myth丶恋晨 2022-07-12 08:16 205阅读 0赞

在上一篇博客[ springMVC源码分析--页面跳转RedirectView（三）][springMVC_--_RedirectView]中我们看到了在RedirectView跳转时会将跳转之前的请求中的参数保存到fFlashMap中，然后通过FlashManager保存起来。

protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request,  
                HttpServletResponse response) throws IOException {  
            //创建跳转链接  
            String targetUrl = createTargetUrl(model, request);  
            targetUrl = updateTargetUrl(targetUrl, model, request, response);  
            //获取原请求所携带的数据  
            FlashMap flashMap = RequestContextUtils.getOutputFlashMap(request);  
            if (!CollectionUtils.isEmpty(flashMap)) {  
                UriComponents uriComponents = UriComponentsBuilder.fromUriString(targetUrl).build();  
                flashMap.setTargetRequestPath(uriComponents.getPath());  
                flashMap.addTargetRequestParams(uriComponents.getQueryParams());  
                FlashMapManager flashMapManager = RequestContextUtils.getFlashMapManager(request);  
                if (flashMapManager == null) {  
                    throw new IllegalStateException("FlashMapManager not found despite output FlashMap having been set");  
                }  
                //将数据保存起来，作为跳转之后请求的数据使用  
                flashMapManager.saveOutputFlashMap(flashMap, request, response);  
            }  
            //重定向操作  
            sendRedirect(request, response, targetUrl, this.http10Compatible);  
        }

接下来我们分别认识一下FlashMap和FalshMapManager

FlashMapManager是一个接口，定义了保存FlashMap和获取FlashMap的方法。

![Image 1][]

public interface FlashMapManager {
    
    	//从session中获取flashMap
    	FlashMap retrieveAndUpdate(HttpServletRequest request, HttpServletResponse response);
    
    	//将falshMap保存到session中
    	void saveOutputFlashMap(FlashMap flashMap, HttpServletRequest request, HttpServletResponse response);
    
    }

两个实现方法都在AbstractFlashMapManager抽象方法中：

saveOutputFlashMap方法实现如下

@Override
    	public final void saveOutputFlashMap(FlashMap flashMap, HttpServletRequest request, HttpServletResponse response) {
    		if (CollectionUtils.isEmpty(flashMap)) {
    			return;
    		}
    		String path = decodeAndNormalizePath(flashMap.getTargetRequestPath(), request);
    		flashMap.setTargetRequestPath(path);
    		if (logger.isDebugEnabled()) {
    			logger.debug("Saving FlashMap=" + flashMap);
    		}
    		flashMap.startExpirationPeriod(getFlashMapTimeout());
    
    		Object mutex = getFlashMapsMutex(request);
    		if (mutex != null) {
    			synchronized (mutex) {
    				List<FlashMap> allFlashMaps = retrieveFlashMaps(request);
    				allFlashMaps = (allFlashMaps != null ? allFlashMaps : new CopyOnWriteArrayList<FlashMap>());
    				allFlashMaps.add(flashMap);
    				//flashMap是在子类SessionFlashManager中
    				updateFlashMaps(allFlashMaps, request, response);
    			}
    		}
    		else {
    			List<FlashMap> allFlashMaps = retrieveFlashMaps(request);
    			allFlashMaps = (allFlashMaps != null ? allFlashMaps : new LinkedList<FlashMap>());
    			allFlashMaps.add(flashMap);
    		    //flashMap是在子类SessionFlashManager中
    			updateFlashMaps(allFlashMaps, request, response);
    		}
    	}

updateFlashMaps方法的实现机制就是将数据保存的请求的Session中，这样跳转后的请求可以从Session中获取数据，并且所有的实现都保存在同一个Session中，为了防止不同重定向请求的数据相互影响，这边有锁进行处理控制。

@Override
    	protected void updateFlashMaps(List<FlashMap> flashMaps, HttpServletRequest request, HttpServletResponse response) {
    		WebUtils.setSessionAttribute(request, FLASH_MAPS_SESSION_ATTRIBUTE, (!flashMaps.isEmpty() ? flashMaps : null));
    	}

retrieveAndUpdate获取FlashMap的实现如下：

@Override
    	public final FlashMap retrieveAndUpdate(HttpServletRequest request, HttpServletResponse response) {
    		List<FlashMap> allFlashMaps = retrieveFlashMaps(request);
    		........
    	}

retrieveFlashMaps中的实现机制就是从Session中获取数据

@Override
    	@SuppressWarnings("unchecked")
    	protected List<FlashMap> retrieveFlashMaps(HttpServletRequest request) {
    		HttpSession session = request.getSession(false);
    		return (session != null ? (List<FlashMap>) session.getAttribute(FLASH_MAPS_SESSION_ATTRIBUTE) : null);
    	}

当重定向的请求在浏览器中重定向之后会进入的DispatcherServlet的doService方法

@Override
    	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
    
    		........
    		
    		//从Session中获取保存的FlashMap中的值
    		FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
    		if (inputFlashMap != null) {
    			request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
    		}
    		//将值保存到request中。这样就不需要通过浏览器跳转组装链接来传递参数了
    		request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
    		request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
    
    		.......
    		
    	}

FlashMap简单来说就是一个HashMap，用于数据保存。

public final class FlashMap extends HashMap<String, Object> implements Comparable<FlashMap> {
    
    	private String targetRequestPath;
    
    	private final MultiValueMap<String, String> targetRequestParams = new LinkedMultiValueMap<String, String>(4);
    
    	private long expirationTime = -1;
    
    	public void setTargetRequestPath(String path) {
    		this.targetRequestPath = path;
    	}
    	public String getTargetRequestPath() {
    		return this.targetRequestPath;
    	}
    	public FlashMap addTargetRequestParams(MultiValueMap<String, String> params) {
    		if (params != null) {
    			for (String key : params.keySet()) {
    				for (String value : params.get(key)) {
    					addTargetRequestParam(key, value);
    				}
    			}
    		}
    		return this;
    	}
    
    	
    	public FlashMap addTargetRequestParam(String name, String value) {
    		if (StringUtils.hasText(name) && StringUtils.hasText(value)) {
    			this.targetRequestParams.add(name, value);
    		}
    		return this;
    	}
    
    	public MultiValueMap<String, String> getTargetRequestParams() {
    		return this.targetRequestParams;
    	}
    
    	public void startExpirationPeriod(int timeToLive) {
    		this.expirationTime = System.currentTimeMillis() + timeToLive * 1000;
    	}
    
    	public void setExpirationTime(long expirationTime) {
    		this.expirationTime = expirationTime;
    	}
    
    	public long getExpirationTime() {
    		return this.expirationTime;
    	}
    
    	public boolean isExpired() {
    		return (this.expirationTime != -1 && System.currentTimeMillis() > this.expirationTime);
    	}
    
    	@Override
    	public int compareTo(FlashMap other) {
    		int thisUrlPath = (this.targetRequestPath != null ? 1 : 0);
    		int otherUrlPath = (other.targetRequestPath != null ? 1 : 0);
    		if (thisUrlPath != otherUrlPath) {
    			return otherUrlPath - thisUrlPath;
    		}
    		else {
    			return other.targetRequestParams.size() - this.targetRequestParams.size();
    		}
    	}
    
    	@Override
    	public boolean equals(Object other) {
    		if (this == other) {
    			return true;
    		}
    		if (!(other instanceof FlashMap)) {
    			return false;
    		}
    		FlashMap otherFlashMap = (FlashMap) other;
    		return (super.equals(otherFlashMap) &&
    				ObjectUtils.nullSafeEquals(this.targetRequestPath, otherFlashMap.targetRequestPath) &&
    				this.targetRequestParams.equals(otherFlashMap.targetRequestParams));
    	}
    
    	@Override
    	public int hashCode() {
    		int result = super.hashCode();
    		result = 31 * result + ObjectUtils.nullSafeHashCode(this.targetRequestPath);
    		result = 31 * result + this.targetRequestParams.hashCode();
    		return result;
    	}
    
    	@Override
    	public String toString() {
    		return "FlashMap [attributes=" + super.toString() + ", targetRequestPath=" +
    				this.targetRequestPath + ", targetRequestParams=" + this.targetRequestParams + "]";
    	}
    
    }

[springMVC_--_RedirectView]: http://blog.csdn.net/qq924862077/article/details/55668451
[Image 1]: