原始碼分析過濾器與攔截器的區別

博主最近剛拿到一個微服務的新專案，邊研究邊分析從框架基礎開始慢慢帶領大家研究微服務的一些東西，這次給大家分析下Springboot中的過濾器和攔截器的區別，雖然上次分析過過濾器，但是主要是分析的cas流程，所以就沒太深入，大家也可以看一下的啊

cas原始碼分析：https://www.cnblogs.com/guoxiaoyu/p/13280259.html

好的，正題開始：首先講解一下Springboot中如何進行添加過濾器、進行過濾器過濾請求，添加示例必須來一下

 1 @Configuration
 2 public class WebConfiguration{
 3 
 4 @Bean
 5     public FilterRegistrationBean testFilterByMe(){
 6         FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
 7         filterRegistrationBean.setFilter(new TestFilterByMe());
 8         filterRegistrationBean.setOrder(1);
 9         return filterRegistrationBean;
10     }
11 }

　　我們過濾器為什么要添加到FilterRegistrationBean中，不添加可不可以，為什么用@WebFilter注解也可以呢，用@Component可不可以以的呢？博主今天就通過原始碼給大家講解一下這幾個問題

　　首先我們的Springboot開始啟動后，會進行創建bean和web服務器tomcat，原始碼附上：

 1 @Override
 2     protected void onRefresh() {
 3     //onRefresh方法就是掃描包，決議配置類的程序，原生spring中是一個空方法，這里進行重寫用于創建tomcat服務器
 4         super.onRefresh();
 5         try {
 6             //開始創建web服務器tomcat，所以Springboot才可以不依賴web容器，自己就可以啟動成功并進行訪問
 7             createWebServer();
 8         }
 9         catch (Throwable ex) {
10             throw new ApplicationContextException("Unable to start web server", ex);
11         }
12     }

　　createWebServer()這個方法的原始碼我就不貼上了，大家可以自己看一下原始碼，最后就會看到new tomcat（）；并進行啟動tomcat，啟動容器后當然是開始進行初始化，

1 private void selfInitialize(ServletContext servletContext) throws ServletException {
2         prepareWebApplicationContext(servletContext);
3         registerApplicationScope(servletContext);
4         WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
5         //getServletContextInitializerBeans()這個方法進開始進行決議并添加filter過濾器 了
6         for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
7             beans.onStartup(servletContext);
8         }
9     }

　　現在才到了添加過濾器最關鍵的部分，這個部分已經基本把上面的三個問題的答案告訴大家了，詳情原始碼如下：

 1 //開始添加過濾器
 2     public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
 3             Class<? extends ServletContextInitializer>... initializerTypes) {
 4         this.initializers = new LinkedMultiValueMap<>();
 5         this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes)
 6                 : Collections.singletonList(ServletContextInitializer.class);
 7         //這里實作的添加形式是通過FilterRegistrationBean型別注冊的
 8         addServletContextInitializerBeans(beanFactory);
 9         //這里是通過beanfactory中獲取filter型別過濾器后添加進來的,這就明白了，只要讓spring掃描到，
10         //過濾器自己實作了filter介面，你就會給添加到過濾器鏈
11         addAdaptableBeans(beanFactory);
12         //都會添加到initializers這一個map中
13         List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream()
14                 .flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
15                 .collect(Collectors.toList());
16         this.sortedList = Collections.unmodifiableList(sortedInitializers);
17         logMappings(this.initializers);
18     }

　　一個一個方法分析一下，讓大家看個明白到底是怎么回事，為什么這三種方法都可以實作添加過濾器

 1 //獲取我們的實作FilterRegistrationBean類的過濾器
 2     private void addServletContextInitializerBeans(ListableBeanFactory beanFactory) {
 3         for (Class<? extends ServletContextInitializer> initializerType : this.initializerTypes) {
 4             //獲取type為ServletContextInitializer的排好序的類，跟是否實作order類無關！
 5             for (Entry<String, ? extends ServletContextInitializer> initializerBean : getOrderedBeansOfType(beanFactory,
 6                     initializerType)) {
 7                    //這時候就開始判斷實作FilterRegistrationBean類的過濾器
 8                 addServletContextInitializerBean(initializerBean.getKey(), initializerBean.getValue(), beanFactory);
 9             }
10         }
11     }

獲取bean時debug，觀察一下，最后會篩選出來我們FilterRegistrationBean的過濾器，為什么呢？因為這個類的上級實作了ServletContextInitializer

 　　再來看一下添加的程序，就知道filter要注冊到FilterRegistrationBean中的原因了，

 1 private void addServletContextInitializerBean(String beanName, ServletContextInitializer initializer,
 2             ListableBeanFactory beanFactory) {
 3         if (initializer instanceof ServletRegistrationBean) {
 4             Servlet source = ((ServletRegistrationBean<?>) initializer).getServlet();
 5             addServletContextInitializerBean(Servlet.class, beanName, initializer, beanFactory, source);
 6         }
 7         //在這里進行的添加的程序
 8         else if (initializer instanceof FilterRegistrationBean) {
 9             Filter source = ((FilterRegistrationBean<?>) initializer).getFilter();
10             addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
11         }
12         else if (initializer instanceof DelegatingFilterProxyRegistrationBean) {
13             String source = ((DelegatingFilterProxyRegistrationBean) initializer).getTargetBeanName();
14             addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
15         }
16         else if (initializer instanceof ServletListenerRegistrationBean) {
17             EventListener source = ((ServletListenerRegistrationBean<?>) initializer).getListener();
18             addServletContextInitializerBean(EventListener.class, beanName, initializer, beanFactory, source);
19         }
20         else {
21             addServletContextInitializerBean(ServletContextInitializer.class, beanName, initializer, beanFactory,
22                     initializer);
23         }
24     }

　　我們再來看一下另一種添加的方法

 1 //另一種添加過濾器的方法在這里
 2     protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
 3         MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
 4         addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig));
 5         //從bean工廠中獲取為Filter型別的類，所以只要我們把我們已經實作Filter介面的類交給spring，beanFactory中有我們的類就可以實作
 6         addAsRegistrationBean(beanFactory, Filter.class, new FilterRegistrationBeanAdapter());
 7         for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) {
 8             addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType,
 9                     new ServletListenerRegistrationBeanAdapter());
10         }
11     }

　　其實最后獲取出來后，都是進行創建FilterRegistrationBean

 1 private <T, B extends T> void addAsRegistrationBean(ListableBeanFactory beanFactory, Class<T> type,
 2             Class<B> beanType, RegistrationBeanAdapter<T> adapter) {
 3             //從beanfactory中獲取為filter型別的bean
 4         List<Map.Entry<String, B>> entries = getOrderedBeansOfType(beanFactory, beanType, this.seen);
 5         for (Entry<String, B> entry : entries) {
 6             String beanName = entry.getKey();
 7             B bean = entry.getValue();
 8             if (this.seen.add(bean)) {
 9                 //剩下其他自動實作的創建程序，也是創建一個FilterRegistrationBean并回傳
10                 RegistrationBean registration = adapter.createRegistrationBean(beanName, bean, entries.size());
11                 int order = getOrder(bean);
12                 registration.setOrder(order);
13                 this.initializers.add(type, registration);
14                 if (logger.isTraceEnabled()) {
15                     logger.trace("Created " + type.getSimpleName() + " initializer for bean '" + beanName + "'; order="
16                             + order + ", resource=" + getResourceDescription(beanName, beanFactory));
17                 }
18             }
19         }
20     }
21         @Override
22         public RegistrationBean createRegistrationBean(String name, Filter source, int totalNumberOfSourceBeans) {
23             FilterRegistrationBean<Filter> bean = new FilterRegistrationBean<>(source);
24             bean.setName(name);
25             return bean;
26         }

 　　現在已經把過濾器找的了并且已經添加成功了，開始進行注冊時呼叫的是onstartup方法，注冊到filterDefs這個map中，下面初始化會用到

 　　這里開始進行過濾器的初始化，new ApplicationFilterConfig方法就需要大家自己去debug了，至少加深一下印象，里面會進行初始化，呼叫init方法

 1 //開始過濾器的初始化
 2     public boolean filterStart() {
 3 
 4         if (getLogger().isDebugEnabled()) {
 5             getLogger().debug("Starting filters");
 6         }
 7         // Instantiate and record a FilterConfig for each defined filter
 8         boolean ok = true;
 9         synchronized (filterConfigs) {
10             filterConfigs.clear();
11             //filterDefs這個map就是剛才添加進來的過濾器map
12             for (Entry<String,FilterDef> entry : filterDefs.entrySet()) {
13                 String name = entry.getKey();
14                 if (getLogger().isDebugEnabled()) {
15                     getLogger().debug(" Starting filter '" + name + "'");
16                 }
17                 try {
18                 //在這里會進行fileter的init方法
19                     ApplicationFilterConfig filterConfig =
20                             new ApplicationFilterConfig(this, entry.getValue());
21                     filterConfigs.put(name, filterConfig);
22                 } catch (Throwable t) {
23                     t = ExceptionUtils.unwrapInvocationTargetException(t);
24                     ExceptionUtils.handleThrowable(t);
25                     getLogger().error(sm.getString(
26                             "standardContext.filterStart", name), t);
27                     ok = false;
28                 }
29             }
30         }

　　到這里，過濾器初始化就完成了也把開頭的三個問題給大家講解明白了，剩下的就是過濾請求的程序了，看一下請求過來時的原始碼處理

 1 // Create the filter chain for this request
 2         //當有請求過來時，首先會呼叫過濾器，進行過濾，這里會進行過濾器陣列的創建
 3         ApplicationFilterChain filterChain =
 4                 ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
 5 
 6         // Call the filter chain for this request
 7         // NOTE: This also calls the servlet's service() method
 8         Container container = this.container;
 9         try {
10             if ((servlet != null) && (filterChain != null)) {
11                 // Swallow output if needed
12                 if (context.getSwallowOutput()) {
13                     try {
14                         SystemLogHandler.startCapture();
15                         if (request.isAsyncDispatching()) {
16                             request.getAsyncContextInternal().doInternalDispatch();
17                         } else {
18                             filterChain.doFilter(request.getRequest(),
19                                     response.getResponse());
20                         }
21                     } finally {
22                         String log = SystemLogHandler.stopCapture();
23                         if (log != null && log.length() > 0) {
24                             context.getLogger().info(log);
25                         }
26                     }
27                 } else {
28                     if (request.isAsyncDispatching()) {
29                         request.getAsyncContextInternal().doInternalDispatch();
30                     } else {
31                         filterChain.doFilter
32                             (request.getRequest(), response.getResponse());
33                     }
34                 }
35 
36             }

 1 //陣列結構可以在這里查看
 2     void addFilter(ApplicationFilterConfig filterConfig) {
 3 
 4         // Prevent the same filter being added multiple times
 5         for(ApplicationFilterConfig filter:filters)
 6             if(filter==filterConfig)
 7                 return;
 8 
 9         if (n == filters.length) {
10             ApplicationFilterConfig[] newFilters =
11                 new ApplicationFilterConfig[n + INCREMENT];
12             System.arraycopy(filters, 0, newFilters, 0, n);
13             filters = newFilters;
14         }
15         filters[n++] = filterConfig;
16 
17     }

　　創建后會進行對請求的過濾，原始碼：

 1 //過濾器開始過濾
 2 private void internalDoFilter(ServletRequest request,
 3                                   ServletResponse response)
 4         throws IOException, ServletException {
 5 
 6         // Call the next filter if there is one
 7         //過濾器陣列大小
 8         if (pos < n) {
 9         //每呼叫一次都會從陣列中自增1 pos++
10             ApplicationFilterConfig filterConfig = filters[pos++];
11             try {
12                 Filter filter = filterConfig.getFilter();
13 
14                 if (request.isAsyncSupported() && "false".equalsIgnoreCase(
15                         filterConfig.getFilterDef().getAsyncSupported())) {
16                     request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
17                 }
18                 if( Globals.IS_SECURITY_ENABLED ) {
19                     final ServletRequest req = request;
20                     final ServletResponse res = response;
21                     Principal principal =
22                         ((HttpServletRequest) req).getUserPrincipal();
23 
24                     Object[] args = new Object[]{req, res, this};
25                     SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);
26                 } else {
27                     //每次都會呼叫doFilter方法，在doFilter方法中呼叫internalDoFilter，就是一直回呼，直到所有過濾器走完
28                     filter.doFilter(request, response, this);
29                 }
30             } catch (IOException | ServletException | RuntimeException e) {
31                 throw e;
32             } catch (Throwable e) {
33                 e = ExceptionUtils.unwrapInvocationTargetException(e);
34                 ExceptionUtils.handleThrowable(e);
35                 throw new ServletException(sm.getString("filterChain.filter"), e);
36             }
37             //當有過濾器直接回傳，并沒有繼續回呼時，回直接return，不會處理該請求，就是下面的步驟
38             return;
39         }
40         //當所有過濾器走完后，將會處理請求
41         // We fell off the end of the chain -- call the servlet instance
42         try {
43             if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
44                 lastServicedRequest.set(request);
45                 lastServicedResponse.set(response);
46             }
47 
48             if (request.isAsyncSupported() && !servletSupportsAsync) {
49                 request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
50                         Boolean.FALSE);
51             }
52             // Use potentially wrapped request from this point
53             if ((request instanceof HttpServletRequest) &&
54                     (response instanceof HttpServletResponse) &&
55                     Globals.IS_SECURITY_ENABLED ) {
56                 final ServletRequest req = request;
57                 final ServletResponse res = response;
58                 Principal principal =
59                     ((HttpServletRequest) req).getUserPrincipal();
60                 Object[] args = new Object[]{req, res};
61                 SecurityUtil.doAsPrivilege("service",
62                                            servlet,
63                                            classTypeUsedInService,
64                                            args,
65                                            principal);
66             } else {
67             //就是這里直接呼叫dsipatcherservlet的service方法去轉發doget，dopost方法的，
68             //剩下的就是攔截器的知識點了:
69                 servlet.service(request, response);
70             }
71         } catch (IOException | ServletException | RuntimeException e) {
72             throw e;
73         } catch (Throwable e) {
74             e = ExceptionUtils.unwrapInvocationTargetException(e);
75             ExceptionUtils.handleThrowable(e);
76             throw new ServletException(sm.getString("filterChain.servlet"), e);
77         } finally {
78             if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
79                 lastServicedRequest.set(null);
80                 lastServicedResponse.set(null);
81             }
82         }
83     }

　　到此創建以及過濾請求的流程分析也就結束了，關于URL過濾的問題，匹配的時候只會識別斜杠/和*不要以為？后面的引數也算到URL過濾里，匹配完路徑就完了，然后和攔截器的創建以及攔截分析做一下對比，分析一下兩者的區別，如果不知道攔截器的創建以及流程處理可以看一下我的另一篇文章：https://www.cnblogs.com/guoxiaoyu/p/13402861.html

相同點：

1. 都需要交給spring進行管理，雖然filter本身是servlet，但是如果不給spring管理，根本不會添加成功，也不會過濾請求
2. 都會在請求真正被處理前進行攔截過濾，如果不符合條件會直接回傳，不會處理請求
3. 兩者都可以指定執行順序

差異點：

1. 過濾器先注冊，攔截器后注冊
2. 過濾器先執行，攔截器后執行，攔截器可以在請求執行后繼續處理其他事情，過濾器只有一個過濾的方法
3. 過濾器執行時是基于函式回呼，而攔截器執行是直接從陣列中獲取，一個一個執行，作者沒有看到哪里用到了反射，網上好多說是反射，攔截器的三個方法都是從陣列中獲取然后一個一個呼叫方法進行的，只有在處理請求的時候才用到了invoke反射

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