源码分析过滤器与拦截器的区别

博主最近刚拿到一个微服务的新项目，边研究边分析从框架基础开始慢慢带领大家研究微服务的一些东西，这次给大家分析下Springboot中的过滤器和拦截器的区别。虽然上次分析过过滤器，但是主要是分析的cas流程，所以就没太深入，大家也可以看一下的啊

cas源码分析：www.cnblogs.com/guoxiaoyu/p...

好的，正题开始：首先讲解一下Springboot中如何进行添加过滤器、进行过滤器过滤请求。添加示例必须来一下

java 复制代码

 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 }

过滤器示例

我们过滤器为什么要添加到FilterRegistrationBean中，不添加可不可以，为什么用@WebFilter注解也可以呢，用@Component可不可以以的呢？博主今天就通过源码给大家讲解一下这几个问题

首先我们的Springboot开始启动后，会进行创建bean和web服务器tomcat，源码附上：

typescript 复制代码

 1 @Override
 2     protected void onRefresh() {
 3     //onRefresh方法就是扫描包，解析配置类的过程，原生spring中是一个空方法，这里进行重写用于创建tomcat服务器
 4         super.onRefresh();
 5         try {
 6             //开始创建web服务器tomcat，所以Springboot才可以不依赖web容器，自己就可以启动成功并进行访问
 7             createWebServer();
 8         }
 9         catch (Throwable ex) {
10             throw new ApplicationContextException("Unable to start web server", ex);
11         }
12     }

org/springframework/boot/web/servlet/context/ServletWebServerApplicationContext

createWebServer()这个方法的源码我就不贴上了，大家可以自己看一下源码，最后就会看到new tomcat（）；并进行启动tomcat。启动容器后当然是开始进行初始化。

scss 复制代码

1 private void selfInitialize(ServletContext servletContext) throws ServletException {
2         prepareWebApplicationContext(servletContext);
3         registerApplicationScope(servletContext);
4         WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
5         //getServletContextInitializerBeans()这个方法进开始进行解析并添加filter过滤器 了
6         for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
7             beans.onStartup(servletContext);
8         }
9     }

org/springframework/boot/web/servlet/context/ServletWebServerApplicationContext

现在才到了添加过滤器最关键的部分，这个部分已经基本把上面的三个问题的答案告诉大家了，详情源码如下：

scss 复制代码

 1 //开始添加过滤器
 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         //这里实现的添加形式是通过FilterRegistrationBean类型注册的
 8         addServletContextInitializerBeans(beanFactory);
 9         //这里是通过beanfactory中获取filter类型过滤器后添加进来的,这就明白了，只要让spring扫描到，
10         //过滤器自己实现了filter接口，你就会给添加到过滤器链
11         addAdaptableBeans(beanFactory);
12         //都会添加到initializers这一个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     }

org/springframework/boot/web/servlet/ServletContextInitializerBeans

一个一个方法分析一下，让大家看个明白到底是怎么回事，为什么这三种方法都可以实现添加过滤器

typescript 复制代码

 1 //获取我们的实现FilterRegistrationBean类的过滤器
 2     private void addServletContextInitializerBeans(ListableBeanFactory beanFactory) {
 3         for (Class<? extends ServletContextInitializer> initializerType : this.initializerTypes) {
 4             //获取type为ServletContextInitializer的排好序的类，跟是否实现order类无关！
 5             for (Entry<String, ? extends ServletContextInitializer> initializerBean : getOrderedBeansOfType(beanFactory,
 6                     initializerType)) {
 7                    //这时候就开始判断实现FilterRegistrationBean类的过滤器
 8                 addServletContextInitializerBean(initializerBean.getKey(), initializerBean.getValue(), beanFactory);
 9             }
10         }
11     }

org/springframework/boot/web/servlet/ServletContextInitializerBeans.java

获取bean时debug，观察一下，最后会筛选出来我们FilterRegistrationBean的过滤器，为什么呢？因为这个类的上级实现了ServletContextInitializer

再来看一下添加的过程，就知道filter要注册到FilterRegistrationBean中的原因了，

scss 复制代码

 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         //在这里进行的添加的过程
 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     }

org/springframework/boot/web/servlet/ServletContextInitializerBeans

我们再来看一下另一种添加的方法

scss 复制代码

 1 //另一种添加过滤器的方法在这里
 2     protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
 3         MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
 4         addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig));
 5         //从bean工厂中获取为Filter类型的类，所以只要我们把我们已经实现Filter接口的类交给spring，beanFactory中有我们的类就可以实现
 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     }

org/springframework/boot/web/servlet/ServletContextInitializerBeans

其实最后获取出来后，都是进行创建FilterRegistrationBean

typescript 复制代码

 1 private <T, B extends T> void addAsRegistrationBean(ListableBeanFactory beanFactory, Class<T> type,
 2             Class<B> beanType, RegistrationBeanAdapter<T> adapter) {
 3             //从beanfactory中获取为filter类型的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                 //剩下其他自动实现的创建过程，也是创建一个FilterRegistrationBean并返回
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         }

org/springframework/boot/web/servlet/ServletContextInitializerBeans

现在已经把过滤器找的了并且已经添加成功了，开始进行注册时调用的是onstartup方法，注册到filterDefs这个map中，下面初始化会用到

这里开始进行过滤器的初始化，new ApplicationFilterConfig方法就需要大家自己去debug了，至少加深一下印象，里面会进行初始化，调用init方法

scss 复制代码

 1 //开始过滤器的初始化
 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这个map就是刚才添加进来的过滤器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                 //在这里会进行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         }

org/apache/catalina/core/StandardContext

到这里，过滤器初始化就完成了也把开头的三个问题给大家讲解明白了，剩下的就是过滤请求的过程了，看一下请求过来时的源码处理

scss 复制代码

 1 // Create the filter chain for this request
 2         //当有请求过来时，首先会调用过滤器，进行过滤，这里会进行过滤器数组的创建
 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             }

org/apache/catalina/core/StandardWrapperValve

ini 复制代码

 1 //数组结构可以在这里查看
 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     }

ApplicationFilter数据结构

创建后会进行对请求的过滤，源码：

scss 复制代码

 1 //过滤器开始过滤
 2 private void internalDoFilter(ServletRequest request,
 3                                   ServletResponse response)
 4         throws IOException, ServletException {
 5 
 6         // Call the next filter if there is one
 7         //过滤器数组大小
 8         if (pos < n) {
 9         //每调用一次都会从数组中自增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                     //每次都会调用doFilter方法，在doFilter方法中调用internalDoFilter，就是一直回调，直到所有过滤器走完
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             //当有过滤器直接返回，并没有继续回调时，回直接return，不会处理该请求，就是下面的步骤
38             return;
39         }
40         //当所有过滤器走完后，将会处理请求
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             //就是这里直接调用dsipatcherservlet的service方法去转发doget，dopost方法的，
68             //剩下的就是拦截器的知识点了:
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     }

org/apache/catalina/core/ApplicationFilterChain

到此创建以及过滤请求的流程分析也就结束了，关于URL过滤的问题，匹配的时候只会识别斜杠/和*不要以为？后面的参数也算到URL过滤里，匹配完路径就完了，然后和拦截器的创建以及拦截分析做一下对比，分析一下两者的区别，如果不知道拦截器的创建以及流程处理可以看一下我的另一篇文章：www.cnblogs.com/guoxiaoyu/p...

相同点：

都需要交给spring进行管理，虽然filter本身是servlet，但是如果不给spring管理，根本不会添加成功，也不会过滤请求
都会在请求真正被处理前进行拦截过滤，如果不符合条件会直接返回，不会处理请求
两者都可以指定执行顺序

差异点：

过滤器先注册，拦截器后注册
过滤器先执行，拦截器后执行，拦截器可以在请求执行后继续处理其他事情，过滤器只有一个过滤的方法
过滤器执行时是基于函数回调，而拦截器执行是直接从数组中获取，一个一个执行，作者没有看到哪里用到了反射，网上好多说是反射，拦截器的三个方法都是从数组中获取然后一个一个调用方法进行的，只有在处理请求的时候才用到了invoke反射