序

本文主要對比一下spring mvc中可以使用的幾類攔截器。

分類

主要分Filter及interceptor。

Filter

是servlet規(guī)范中的Filter，spring中有一個基本的實現(xiàn)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();
    }
}
//......

這個類主要實現(xiàn)了spring生命周期的幾個接口，方便作為bean納入IOC容器管理。
如果是在web.xml定義的話，支持將參數(shù)映射到bean中的屬性

OncePerRequestFilter

在spring中，filter都默認繼承OncePerRequestFilter,他確保一次請求只通過一次filter，而不重復(fù)執(zhí)行。

此方式是為了兼容不同的web container，特意而為之（JSR168），也就是說并不是所有的container都像我們期望的只過濾一次，servlet版本不同.為了兼容各種不同的運行環(huán)境和版本，默認filter繼承OncePerRequestFilter是一個比較穩(wěn)妥的選擇。

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;
    }
  //......
}

通過filtername+ALREADY_FILTERED_SUFFIX來標(biāo)識filter是否已經(jīng)執(zhí)行過。

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來執(zhí)行

public interface HandlerInterceptor {

    /**
     * Intercept the execution of a handler. Called after HandlerMapping determined
     * an appropriate handler object, but before HandlerAdapter invokes the handler.
     * <p>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.
     * <p><strong>Note:</strong> 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.
     * <p>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.
     * <p><strong>Note:</strong> 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.
     * <p>Note: Will only be called if this interceptor's {@code preHandle}
     * method has successfully completed and returned {@code true}!
     * <p>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.
     * <p><strong>Note:</strong> 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;

}

主要定義了三個方法，preHandle，postHandle，afterCompletion

• preHandle
  這個里頭返回false，則會停止繼續(xù)往下執(zhí)行
• postHandle
  后處理回調(diào)方法，實現(xiàn)處理器的后處理，但在渲染視圖之前執(zhí)行，可以在這里額外往視圖添加額外的變量等(在preHandle成功執(zhí)行完，返回true的情況下執(zhí)行)
• afterCompletion
  在preHandle成功執(zhí)行完，返回true的情況下執(zhí)行.整個請求處理完畢回調(diào)方法，即在視圖渲染完畢時回調(diào)

對比

記錄耗時等用filter的比較多，比較全面；執(zhí)行鑒權(quán)相關(guān)的用HandlerInterceptor的比較多，當(dāng)然用filter也可以。

doc

• Filters and Spring