springmvc的关于拦截器的讨论

拼搏现实的明天。 2022-12-12 13:42 154阅读 0赞

## 1：接口定义 ##

springMVC的拦截器对应的接口是`org.springframework.web.servlet.HandlerInterceptor`,接口定义如下：

public interface HandlerInterceptor { 
    	// <1>
    	default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
    			throws Exception { 
    		return true;
    	}
    	// <2>
    	default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
    			@Nullable ModelAndView modelAndView) throws Exception { 
    	}
    	// <3>
    	default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
    			@Nullable Exception ex) throws Exception { 
    	}
    }

`<1>`方法`preHandle(req, res, handler)`是在调用目标handler之前调用，`<2>`方法`postHandle(req, res, handler)`是在调用目标方法成功之后调用，`<3>`方法`afterCompletion(req, res, handler)`是在请求执行完毕之后调用`（不管是执行成功还是执行失败）`，可参考在`org.springframework.web.servlet.DispatcherServlet#doDispatch`调用过程，如下部分涉及拦截器调用源码`（注意：拦截器是封装在HandlerExecutionChain中被调用的）`：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { 
    	try { 
    		try { 
    			// 1：执行目标handler前调用拦截器的preHandle(req, res, handler)
    			if (!mappedHandler.applyPreHandle(processedRequest, response)) { 
    				return;
    			}
    			// 2：执行目标handler
    			mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
    			// 3: 执行目标handler成功后，执行拦截器的postHanlde(req, res, handler)
    			mappedHandler.applyPostHandle(processedRequest, response, mv);
    		}
    		catch (Exception ex) { 
    		}
    		catch (Throwable err) { 
    		}
    		// <branch-1>
    		processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    	}
    	catch (Exception ex) { 
    		// 4.1：执行失败，执行拦截器的afterCompletion(req, res, handler)方法
    		triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
    	}
    	catch (Throwable err) { 
    		// 4.2：执行失败，执行拦截器的afterCompletion(req, res, handler)方法 
    		triggerAfterCompletion(processedRequest, response, mappedHandler,
    				new NestedServletException("Handler processing failed", err));
    	}
    }

另外这里没有请求成功结束后的`afterCompletion(req, res, handler)`方法的调用，其调用是在`<branch-1>`方法中，调用源码如下：

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
    			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
    			@Nullable Exception exception) throws Exception { 
    	// 5：请求处理成功，调用afterCompletion(req, res, handler)
    	if (mappedHandler != null) { 
    		mappedHandler.triggerAfterCompletion(request, response, null);
    	}
    }

既然HandlerInterceptor的调用是通过`org.springframework.web.servlet.HandlerExecutionChain`处理器执行链来调用的，那就来看下这个类。

## 2：HandlerExecutionChain ##

### 2.1：构造方法 ###

一共两个构造函数，一个指定handler，一个指定了handler和拦截器。

public HandlerExecutionChain(Object handler) { 
    	this(handler, (HandlerInterceptor[]) null);
    }
    public HandlerExecutionChain(Object handler, @Nullable HandlerInterceptor... interceptors) { 
    	if (handler instanceof HandlerExecutionChain) { 
    		HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
    		this.handler = originalChain.getHandler();
    		this.interceptorList = new ArrayList<>();
    		CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
    		CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
    	}
    	else { 
    		this.handler = handler;
    		this.interceptors = interceptors;
    	}
    }

在`org.springframework.web.servlet.handler.AbstractHandlerMapping`中使用的是只有hander的构造函数，调用源码如下：

org.springframework.web.servlet.handler.AbstractHandlerMapping#getHandlerExecutionChain
    protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) { 
    	HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
    			(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
    }

### 2.2：主要变量 ###

private final Object handler;
    @Nullable
    private HandlerInterceptor[] interceptors;
    @Nullable
    private List<HandlerInterceptor> interceptorList;
    private int interceptorIndex = -1;

`Object handler`存储目标handler，`interceptors,interceptorList`都是用来存储拦截器的，代码逻辑使用的是`interceptorList`，`interceptors`可以认为只是过度使用，`interceptorIndex`记录已经执行的位置，使用如下：

org.springframework.web.servlet.HandlerExecutionChain#applyPreHandle
    boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception { 
    	...
    	if (!ObjectUtils.isEmpty(interceptors)) { 
    		for (int i = 0; i < interceptors.length; i++) { 
    			...
    			this.interceptorIndex = i;
    		}
    	}
    	return true;
    }

### 2.3：主要方法 ###

*  addInterceptor  
    该方法有两个版本：

public void addInterceptor(HandlerInterceptor interceptor) { }
    public void addInterceptors(HandlerInterceptor... interceptors) { }

在`org.springframework.web.servlet.handler.AbstractHandlerMapping`中使用的是第一个方法。源码：

protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) { 
    	...
    	for (HandlerInterceptor interceptor : this.adaptedInterceptors) { 
    		if (interceptor instanceof MappedInterceptor) { 
    			...
    			if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) { 
    				chain.addInterceptor(mappedInterceptor.getInterceptor());
    			}
    		}
    		else { 
    			...
    		}
    	}
    	return chain;
    }

*  getInterceptors  
    获取拦截器数组，源码：

public HandlerInterceptor[] getInterceptors() { 
    	if (this.interceptors == null && this.interceptorList != null) { 
    		this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[0]);
    	}
    	return this.interceptors;
    }

*  调用目标拦截器  
    三个方法，`applyPreHanlder(req, res)`,`applyPostHandler`,`triggerAfterCompletion`,源码如下：

org.springframework.web.servlet.HandlerExecutionChain#applyPreHandle
    boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception { 
    	HandlerInterceptor[] interceptors = getInterceptors();
    	if (!ObjectUtils.isEmpty(interceptors)) { 
    		for (int i = 0; i < interceptors.length; i++) { 
    			HandlerInterceptor interceptor = interceptors[i];
    			if (!interceptor.preHandle(request, response, this.handler)) { 
    				triggerAfterCompletion(request, response, null);
    				return false;
    			}
    			this.interceptorIndex = i;
    		}
    	}
    	return true;
    }
    
    org.springframework.web.servlet.HandlerExecutionChain#applyPostHandle
    void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
    			throws Exception { 
    
    	HandlerInterceptor[] interceptors = getInterceptors();
    	if (!ObjectUtils.isEmpty(interceptors)) { 
    		for (int i = interceptors.length - 1; i >= 0; i--) { 
    			HandlerInterceptor interceptor = interceptors[i];
    			interceptor.postHandle(request, response, this.handler, mv);
    		}
    	}
    }
    
    org.springframework.web.servlet.HandlerExecutionChain#triggerAfterCompletion
    void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex)
    			throws Exception { 
    
    	HandlerInterceptor[] interceptors = getInterceptors();
    	if (!ObjectUtils.isEmpty(interceptors)) { 
    		for (int i = this.interceptorIndex; i >= 0; i--) { 
    			HandlerInterceptor interceptor = interceptors[i];
    			try { 
    				interceptor.afterCompletion(request, response, this.handler, ex);
    			}
    			catch (Throwable ex2) { 
    				logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
    			}
    		}
    	}
    }

## 3：MappedInterceptor ##

`org.springframework.web.servlet.handler.MappedInterceptor`是`org.springframe,web.servlet.HandlerInterceptor`的子类，类签名：

public final class MappedInterceptor implements HandlerInterceptor { }

通过uml表示：  
![在这里插入图片描述][20201007142207355.png_pic_center]  
我们使用`<mvc:interceptors>`标签配置的拦截器信息就会被解析为MappedInterceptor对象，如下定义：

<mvc:interceptors>
    	<mvc:interceptor>
    		<mvc:mapping path="/testinterceptor/hi"/>
    		<bean class="dongshi.handlerinterceptor.DemoHandlerInterceptor"></bean>
    	</mvc:interceptor>
    	<mvc:interceptor>
    		<mvc:mapping path="/testinterceptor/hi"/>
    		<bean class="dongshi.handlerinterceptor.DemoHandlerInterceptor1"/>
    	</mvc:interceptor>
    </mvc:interceptors>

debug`org.springframework.web.servlet.handler.AbstractHandlerMapping#initApplicationContext#adaptedInterceptors`可以看到，如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmcwOTA3_size_16_color_FFFFFF_t_70_pic_center]

### 3.1：路径匹配方法match ###

源码：

public boolean matches(String lookupPath, PathMatcher pathMatcher) { 
    	PathMatcher pathMatcherToUse = (this.pathMatcher != null ? this.pathMatcher : pathMatcher);
    	// <1>
    	if (!ObjectUtils.isEmpty(this.excludePatterns)) { 
    		for (String pattern : this.excludePatterns) { 
    			if (pathMatcherToUse.match(pattern, lookupPath)) { 
    				return false;
    			}
    		}
    	}
    	// <2>
    	if (ObjectUtils.isEmpty(this.includePatterns)) { 
    		return true;
    	}
    	// <3>
    	for (String pattern : this.includePatterns) { 
    		if (pathMatcherToUse.match(pattern, lookupPath)) { 
    			return true;
    		}
    	}
    	return false;
    }

`<1>`处代码如果通过排除路径集合，过滤，满足排除路径某个则不匹配，`<2>`处代码如果是包含路径为空则认为拦截所有，即匹配。`<3>`通过包含路径集合查看是否匹配，匹配其中一个则认为匹配。到最后说明不匹配，直接返回false。该方法的调用源码如下：

org.springframework.web.servlet.handler.AbstractHandlerMapping#getHandlerExecutionChain
    protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) { 
        ...
    	for (HandlerInterceptor interceptor : this.adaptedInterceptors) { 
    		if (interceptor instanceof MappedInterceptor) { 
    			MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
    			if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) { 
    				chain.addInterceptor(mappedInterceptor.getInterceptor());
    			}
    	}
    	...
    	}
    	return chain;
    }

## 最后：都让开，我要喝瑞幸 ##

![在这里插入图片描述][20200828090303329.png_pic_center]

[20201007142207355.png_pic_center]: /images/20221123/8188e8e63aac4c399006c22a30e8ba34.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmcwOTA3_size_16_color_FFFFFF_t_70_pic_center]: /images/20221123/d7dd2d1ee04849e98c3cc231acc9ca84.png
[20200828090303329.png_pic_center]: /images/20221123/191e1eaad2d844a6a455d9f9e72664a8.png