详解SpringMVC的拦截器链实现及拦截器链配置

拦截器(Interceptor)是一种动态拦截方法调用的机制,在SpringMVC中动态拦截控制器方法的执行。本文将详细讲讲SpringMVC中拦截器参数及拦截器链配置,感兴趣的可以尝试一下

1、拦截器链实现

只需定义多个拦截器的 bean,然后在拦截器的配置类中将其逐一添加即可

第一个拦截器的定义:

@Component
public class ProjectInterceptor1 implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("preHandle111...");
        return true;
    }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle111...");
    }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("afterCompletion111...");
    }
}

第二个拦截器的定义:

@Component
public class ProjectInterceptor2 implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("preHandle222...");
        return true;
    }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle222...");
    }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("afterCompletion222...");
    }
}

拦截器配置类:

@Configuration
public class SpringMvcSupport extends WebMvcConfigurationSupport {
    @Autowired
    private ProjectInterceptor1 interceptor1;
    @Autowired
    private ProjectInterceptor2 interceptor2;
    @Override
    protected void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(interceptor1).addPathPatterns("/books", "/books/*");
        registry.addInterceptor(interceptor2).addPathPatterns("/books", "/books/*");
    }
}

2、拦截器链的执行顺序

拦截器配置类中,首先被添加的拦截器在外层,之后添加的在内层,请求发出之后首先被外层的拦截器拦截,外层放行后进入内层,而离开拦截器时先离开内层的拦截器,再离开外层。

上例子中第一个拦截器在外层,第二个在内层,所以上例中拦截器的输出顺序为:

preHandle111...
preHandle222...
postHandle222...
postHandle111...
afterCompletion222...
afterCompletion111...

值得注意的是,afterCompletion 方法的一定会在 postHandle 之后执行,并且也是由内层向外层执行,所以 afterCompletion222 输出在 postHandle111 之后,而在 afterCompletion111 之前。换言之,即便有再多的拦截器,最先执行的 afterCompletion 也一定在最后执行的 postHandle 之后才执行

此外,当拦截器的 preHandle 方法返回 false 时,其内层的拦截器以及它自身 postHandle 和 afterCompletion 都不会再执行,而所有外层拦截器的 postHandle 不再执行,但 afterCompletion 照常执行

这是因为 postHandle 执行在原始 Controller 方法执行之后,必须所有拦截器都放行时,才会执行原始方法,也就才会执行 postHandle 方法

上例中第二个拦截器 preHandle 返回 false 时的输出顺序:

preHandle111...
preHandle222...
afterCompletion111...

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本文标题为:详解SpringMVC的拦截器链实现及拦截器链配置

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