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本文主要对比一下spring mvc中可以使用的几类拦截器。
分类
主要分Filter及interceptor。
Filter
是servlet规范中的Filter，spring中有一个基本的实现叫做org/springframework/web/filter/GenericFilterBean.java
public abstract class GenericFilterBean implements Filter, BeanNameAware, EnvironmentAware, ServletContextAware, InitializingBean, DisposableBean { @Override public final void setBeanName(String beanName) { this.beanName = beanName; } @Override public void setEnvironment(Environment environment) { this.environment = environment; } @Override public final void setServletContext(ServletContext servletContext) { this.servletContext = servletContext; } @Override public void afterPropertiesSet() throws ServletException { initFilterBean(); }}//...... 这个类主要实现了spring生命周期的几个接口，方便作为bean纳入IOC容器管理。 如果是在web.xml定义的话，支持将参数映射到bean中的属性
OncePerRequestFilter
在spring中，filter都默认继承OncePerRequestFilter,他确保一次请求只通过一次filter，而不重复执行。
此方式是为了兼容不同的web container，特意而为之（JSR168），也就是说并不是所有的container都像我们期望的只过滤一次，servlet版本不同.为了兼容各种不同的运行环境和版本，默认filter继承OncePerRequestFilter是一个比较稳妥的选择。
public abstract class OncePerRequestFilter extends GenericFilterBean {public static final String ALREADY_FILTERED_SUFFIX = ".FILTERED";protected String getAlreadyFilteredAttributeName() { String name = getFilterName(); if (name == null) { name = getClass().getName(); } return name + ALREADY_FILTERED_SUFFIX; } //......} 通过filtername+ALREADY_FILTERED_SUFFIX来标识filter是否已经执行过。
HandlerInterceptor
org/springframework/spring-webmvc/4.3.9.RELEASE/spring-webmvc-4.3.9.RELEASE-sources.jar!/org/springframework/web/servlet/HandlerInterceptor.java
基于execution chains来执行
public interface HandlerInterceptor { /** * Intercept the execution of a handler. Called after HandlerMapping determined * an appropriate handler object, but before HandlerAdapter invokes the handler. * DispatcherServlet processes a handler in an execution chain, consisting * of any number of interceptors, with the handler itself at the end. * With this method, each interceptor can decide to abort the execution chain, * typically sending a HTTP error or writing a custom response. *
Note: special considerations apply for asynchronous * request processing. For more details see * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}. * @param request current HTTP request * @param response current HTTP response * @param handler chosen handler to execute, for type and/or instance evaluation * @return {@code true} if the execution chain should proceed with the * next interceptor or the handler itself. Else, DispatcherServlet assumes * that this interceptor has already dealt with the response itself. * @throws Exception in case of errors */ boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception; /** * Intercept the execution of a handler. Called after HandlerAdapter actually * invoked the handler, but before the DispatcherServlet renders the view. * Can expose additional model objects to the view via the given ModelAndView. *
DispatcherServlet processes a handler in an execution chain, consisting * of any number of interceptors, with the handler itself at the end. * With this method, each interceptor can post-process an execution, * getting applied in inverse order of the execution chain. *
Note: special considerations apply for asynchronous * request processing. For more details see * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}. * @param request current HTTP request * @param response current HTTP response * @param handler handler (or {@link HandlerMethod}) that started asynchronous * execution, for type and/or instance examination * @param modelAndView the {@code ModelAndView} that the handler returned * (can also be {@code null}) * @throws Exception in case of errors */ void postHandle( HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception; /** * Callback after completion of request processing, that is, after rendering * the view. Will be called on any outcome of handler execution, thus allows * for proper resource cleanup. *
Note: Will only be called if this interceptor's {@code preHandle} * method has successfully completed and returned {@code true}! *
As with the {@code postHandle} method, the method will be invoked on each * interceptor in the chain in reverse order, so the first interceptor will be * the last to be invoked. *
Note: special considerations apply for asynchronous * request processing. For more details see * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}. * @param request current HTTP request * @param response current HTTP response * @param handler handler (or {@link HandlerMethod}) that started asynchronous * execution, for type and/or instance examination * @param ex exception thrown on handler execution, if any * @throws Exception in case of errors */ void afterCompletion( HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception;}
主要定义了三个方法，preHandle，postHandle，afterCompletion
- preHandle 这个里头返回false，则会停止继续往下执行
- postHandle 后处理回调方法，实现处理器的后处理，但在渲染视图之前执行，可以在这里额外往视图添加额外的变量等(在preHandle成功执行完，返回true的情况下执行)
- afterCompletion 在preHandle成功执行完，返回true的情况下执行.整个请求处理完毕回调方法，即在视图渲染完毕时回调
对比
|类型|范围|执行链处理|异常|经典实用| |--|--|---------|--|--| |filter|filter是servlet是定义，在支持servlet的容器中都可以支持|doFilter方法没有返回值，每个filter里头去控制是否往下执行，不想往下执行的话，可以自己设定response body和status然后提前返回|异常无法被spring的ExceptionHandler捕获，直接500|CharacterEncodingFilter<br>CorsFilter<br>CsrfFilter<br>MetricsFilter<br>MultipartFilter<br>OpenEntityManagerInViewFilter<br>WebRequestTraceFilter| |HandlerInterceptor|在spring mvc中支持|preHandle方法返回布尔值，当布尔值为true的时候继续往下一个interceptor执行，返回false则立即返回，可以自己设定response body和status,也可以抛异常，spring会统一拦截处理|异常可以被ExceptionHandler捕获|MvcEndpointSecurityInterceptor<br>UserRoleAuthorizationInterceptor|
记录耗时等用filter的比较多，比较全面；执行鉴权相关的用HandlerInterceptor的比较多，当然用filter也可以。