java源码-springmvc

水深无声 2023-07-24 14:54 23阅读 0赞

### 文章目录 ###

*  初始化过程
 *  DispatcherServlet处理请求

![img][]

[https://www.cnblogs.com/Java-Starter/p/10310565.html][https_www.cnblogs.com_Java-Starter_p_10310565.html]

# 初始化过程 #

[https://blog.csdn.net/dhaiuda/article/details/80026354][https_blog.csdn.net_dhaiuda_article_details_80026354]

总结下HttpServletBean,FrameworkServlet和DispatcherServlet初始化过程

1.HttpServletBean

初始化web.xml中的参数

2.FrameworkServlet

将上下文赋予当前Servlet

3.DispatcherServlet

初始化HandlerMapping(请求映射),HandlerExceptionResolver(异常处理),ViewResolver(视图解析)等功能实现类

![img][img 1]

# DispatcherServlet处理请求 #

在浏览器输入http://localhost:8080/springmvcdemo/employee，触发DispatcherServlet的processRequest方法

先看父类FrameworkServlet的processRequest方法:

previousLocaleContext获取和当前线程相关的LocaleContext

根据已有请求构造一个新的和当前线程相关的LocaleContext

previousAttributes获取和当前线程绑定的RequestAttributes

为已有请求构造新的ServletRequestAttributes，加入预绑定属性

initContextHolders让新构造的RequestAttributes和ServletRequestAttributes和当前线程绑定，加入到ThreadLocal，完成绑定

抽象方法doService由FrameworkServlet子类DispatcherServlet重写

![img][img 2]

![img][img 3]

resetContextHolders方法解除RequestAttributes,ServletRequestAttributes和当前线程的绑定

注册监听事件ServletRequestHandledEvent,在调用上下文的时候产生Event

现在我们看下DispatcherServlet的doService方法

![img][img 4]

attributesSnapshot用来保存request域中的数据，可以叫做“快照”

![img][img 5]

进入doDispatch方法

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { 
    		HttpServletRequest processedRequest = request;
    		HandlerExecutionChain mappedHandler = null;
    		boolean multipartRequestParsed = false;
    
    		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    
    		try { 
    			ModelAndView mv = null;
    			Exception dispatchException = null;
    
    			try { 
    				processedRequest = checkMultipart(request);
    				multipartRequestParsed = (processedRequest != request);
    
    				
                    //通过当前request获取到 HandlerExecutionChain
    				mappedHandler = getHandler(processedRequest);
    				if (mappedHandler == null) { 
    					noHandlerFound(processedRequest, response);
    					return;
    				}
    
    				
                    //确定当前请求的处理程序适配器。
    				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
    
    				// 如果处理程序支持，则处理最后修改的标头
    				String method = request.getMethod();
    				boolean isGet = "GET".equals(method);
    				if (isGet || "HEAD".equals(method)) { 
    					long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
    					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { 
    						return;
    					}
    				}
    
    				if (!mappedHandler.applyPreHandle(processedRequest, response)) { 
    					return;
    				}
    
    				// 实际调用处理程序。
    				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
    
    				if (asyncManager.isConcurrentHandlingStarted()) { 
    					return;
    				}
    
    				applyDefaultViewName(processedRequest, mv);
    				mappedHandler.applyPostHandle(processedRequest, response, mv);
    			}
    			catch (Exception ex) { 
    				dispatchException = ex;
    			}
    			catch (Throwable err) { 
    				// As of 4.3, we're processing Errors thrown from handler methods as well,
    				// making them available for @ExceptionHandler methods and other scenarios.
    				dispatchException = new NestedServletException("Handler dispatch failed", err);
    			}
    			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    		}
    		catch (Exception ex) { 
    			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
    		}
    		catch (Throwable err) { 
    			triggerAfterCompletion(processedRequest, response, mappedHandler,
    					new NestedServletException("Handler processing failed", err));
    		}
    		finally { 
    			if (asyncManager.isConcurrentHandlingStarted()) { 
    				// Instead of postHandle and afterCompletion
    				if (mappedHandler != null) { 
    					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
    				}
    			}
    			else { 
    				// Clean up any resources used by a multipart request.
    				if (multipartRequestParsed) { 
    					cleanupMultipart(processedRequest);
    				}
    			}
    		}
    	}

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException { 
       if (this.handlerAdapters != null) { 
          for (HandlerAdapter adapter : this.handlerAdapters) { 
             if (adapter.supports(handler)) { 
                return adapter;
             }
          }
       }
       throw new ServletException("No adapter for handler [" + handler +
             "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
    }

第一个就是：从2个handler中，找合适的控制器

BeanNameUrlHandlerMapping@833153a， XML的配置方式控制器

RequestMappingHandlerMapping@3602f818 注解方式的控制器

第二个就是：从3个Adapter中，找合适的处理器

HttpRequestHandlerAdapter@28dc72d7， SimpleControllerHandlerAdapter@6b712691， XML的配置方式的Adapter、annotation

RequestMappingHandlerAdapter@4d763f47 注解方式的Adapter

[https://blog.csdn.net/abcwanglinyong/article/details/91044492][https_blog.csdn.net_abcwanglinyong_article_details_91044492]

![img][img 6]

1、用户发送请求，被 SpringMVC 的前端控制器 DispatcherServlet 拦截。

2、DispatcherServlet 收到请求后调用 HandlerMapping 处理器映射器。

3、处理器映射器找到具体的处理器，生成处理器执行链HandlerExecutionChain（包含处理器Handler和处理器拦截器集合），返回给 DispatcherServlet。

4、DispatcherServlet 调用 HandlerAdapter 处理器适配器。

5、通过HandlerAdapter处理器适配器找到具体的Controller

6、Controller将模型数据Model封装到 ModelAndView 返回给 HandlerAdapter。

7、HandlerAdapter将模型视图ModelAndView 返回给 DispatcherServlet。

8、DispatcherServlet 将 ModelAndView 传给 ViewReslover 视图解析器。

9、ViewReslover 解析后返回具体的 View。

10、DispatcherServlet 根据 View 进行视图渲染（即将模型数据填充至视图中）。

11、DispatcherServlet 将视图响应给用户。  
给 DispatcherServlet。

8、DispatcherServlet 将 ModelAndView 传给 ViewReslover 视图解析器。

9、ViewReslover 解析后返回具体的 View。

10、DispatcherServlet 根据 View 进行视图渲染（即将模型数据填充至视图中）。

11、DispatcherServlet 将视图响应给用户。

[img]: /images/20230528/b4c2033f440242adbce9fdb9c44eb879.png
[https_www.cnblogs.com_Java-Starter_p_10310565.html]: https://www.cnblogs.com/Java-Starter/p/10310565.html
[https_blog.csdn.net_dhaiuda_article_details_80026354]: https://blog.csdn.net/dhaiuda/article/details/80026354
[img 1]: /images/20230528/128fc54b9d374ec0951abb4fe5281eda.png
[img 2]: /images/20230528/e336798f97a44ff989edde55797dba7a.png
[img 3]: /images/20230528/df04d2771f394d108b9563a7521ec13d.png
[img 4]: /images/20230528/9a6e622ed73040fda97e32fe3ff8ead5.png
[img 5]: /images/20230528/3354b543d4e146319dfd3b0fae7d1690.png
[https_blog.csdn.net_abcwanglinyong_article_details_91044492]: https://blog.csdn.net/abcwanglinyong/article/details/91044492
[img 6]: /images/20230528/618ec43cfda14144a513810e47eeccc8.png