Springboot_07拦截器源码分析

最新推荐文章于 2025-01-21 18:17:20 发布

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最新推荐文章于 2025-01-21 18:17:20 发布

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分类专栏： SpringBoot

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本文深入解析了Spring MVC中拦截器的执行流程，包括preHandle、postHandle以及afterCompletion方法。preHandle按顺序执行，若返回false则会倒序执行afterCompletion；所有拦截器返回true后执行目标方法，postHandle同样倒序调用；在页面渲染完成后或异常发生时也会调用afterCompletion。理解这一流程对于优化和调试Spring MVC应用至关重要。

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源码解析:

preHandle方法:
在这里插入图片描述
applyPrehandle方法详解

	boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		for (int i = 0; i < this.interceptorList.size(); i++) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			if (!interceptor.preHandle(request, response, this.handler)) {
			//如果返回false就!false 就为true,就会执行下面方法,倒序执行afterCompletion方法
				triggerAfterCompletion(request, response, null);
				return false;
			}
			this.interceptorIndex = i;
		}
		return true;
	}

倒序执行我们的afterCompletion方法

void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) {
		for (int i = this.interceptorIndex; i >= 0; i--) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			try {
				interceptor.afterCompletion(request, response, this.handler, ex);
			}
			catch (Throwable ex2) {
				logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
			}
		}
	}

PostHandle:
在这里插入图片描述
applyPostHandle详情:

//从下面可以知道我们的PostHandle也是进行倒序执行的
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
			throws Exception {

		for (int i = this.interceptorList.size() - 1; i >= 0; i--) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			interceptor.postHandle(request, response, this.handler, mv);
		}
	}

processDispatchResult(页面渲染完成之后也会调用):

//页面渲染成功以后,也会执行我们的triggerAfterCompletion方法
	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

		boolean errorView = false;

		if (exception != null) {
			if (exception instanceof ModelAndViewDefiningException) {
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = ((ModelAndViewDefiningException) exception).getModelAndView();
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}

		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			if (errorView) {
				WebUtils.clearErrorRequestAttributes(request);
			}
		}
		else {
			if (logger.isTraceEnabled()) {
				logger.trace("No view rendering, null ModelAndView returned.");
			}
		}

		if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
			// Concurrent handling started during a forward
			return;
		}

		if (mappedHandler != null) {
			// Exception (if any) is already handled..
			//页面渲染成功之后,也会执行
			mappedHandler.triggerAfterCompletion(request, response, null);
		}
	}

期间如果有其他方法出现异常的话,也会执行我们的afterCompletion方法(倒序)
在这里插入图片描述

总结:
1.preHandle:顺序执行preHandle,

2.如果我们的perHandle方法返回false,就倒序输出我们的afterCompletion方法

3.所有拦截器都返回true,执行目标方法

3.posthandle:执行目标方法之后进行调用,倒序输出

4.期间出现异常就会倒序调用我们的afterCompletion

5.页面渲染完成之后也会调用afterCompletion方法