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SpringBoot之拦截器（Interceptor）

news 来源：原创 2024/9/20 13:24:32

前言

在使用 SpringBoot 进行 javaEE 的开发过程中，如果希望添加拦截器，一般会实现 HandlerInterceptor 接口，然后通过 SpringBoot 的机制，将拦截器作用于指定方法上

HandlerInterceptor接口

public interface HandlerInterceptor {default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {return true;}default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {}default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {}}

preHandle：目标方法之前执行，如果存在一个 HandlerInterceptor 的 preHandle 方法返回 false，则不执行目标方法
postHandle：目标方法之后执行
afterCompletion：不管方法执行成功还是失败，都会执行的方法

第一个HandlerInterceptor

创建拦截器 FirstInterceptor

public class FirstInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("preHandle1");return HandlerInterceptor.super.preHandle(request, response, handler);}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("postHandle1");HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("afterCompletion1");HandlerInterceptor.super.afterCompletion(request, response, handler, ex);}
}

创建配置文件 InterceptorConfig

@Configuration
public class InterceptorConfig implements WebMvcConfigurer {@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new FirstInterceptor()).addPathPatterns("/interceptor/*");}
}

创建Controller InterceptorController

@RestController
@RequestMapping(value = "/interceptor")
public class InterceptorController {@GetMapping(value = "/simple")public void simple() {System.out.println("target");}
}

访问链接：http://localhost:8080/interceptor/simple

执行顺序

preHandle → targert → postHandle → afterCompletion

多个 HandlerInterceptor，方法的执行顺序

所有方法都正确执行

创建拦截器 SecondInterceptor、ThirdInterceptor

public class SecondInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("preHandle2");return HandlerInterceptor.super.preHandle(request, response, handler);}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("postHandle2");HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("afterCompletion2");HandlerInterceptor.super.afterCompletion(request, response, handler, ex);}
}public class ThirdInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("preHandle3");return HandlerInterceptor.super.preHandle(request, response, handler);}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("postHandle3");HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("afterCompletion3");HandlerInterceptor.super.afterCompletion(request, response, handler, ex);}
}

修改配置文件 InterceptorConfig

@Configuration
public class InterceptorConfig implements WebMvcConfigurer {@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new FirstInterceptor()).addPathPatterns("/interceptor/*");registry.addInterceptor(new SecondInterceptor()).addPathPatterns("/interceptor/*");registry.addInterceptor(new ThirdInterceptor()).addPathPatterns("/interceptor/*");}
}

访问链接：http://localhost:8080/interceptor/simple

图形化如下所示：

某个 preHandle 方法返回 false （或抛出异常）

将 SecondInterceptor 的 preHandle 方法的返回值改成 false

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {System.out.println("preHandle2");return false;
}

访问链接：http://localhost:8080/interceptor/simple

图形化如下所示：

某个 postHandle 方法返回抛出异常

SecondInterceptor 的 postHandle 方法抛出自定义异常

@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {System.out.println("postHandle2");throw new RuntimeException("自定义异常");
}

访问链接：http://localhost:8080/interceptor/simple

图形化如下所示：

小结

正常执行
1. preHandle 方法顺序执行
2. postHandle 方法逆序执行
3. 执行目标方法
4. afterCompletion 方法逆序执行
某个 preHandle 方法返回 false （或抛出异常）
1. 返回 false （或抛出异常）的拦截器及之前的拦截器的 preHandle 方法顺序执行
2. 返回 false （或抛出异常）之前的拦截器的 afterCompletion 方法逆序执行
某个 postHandle 方法返回抛出异常
1. preHandle 方法顺序执行
2. 抛出异常之前的拦截器的 postHandle 方法逆序执行
3. afterCompletion 方法逆序执行

源码解析

HandlerExecutionChain 添加 Interceptor

AbstractHandlerMapping#getHandlerExecutionChain

我们在上文中展示了三张图，其实它就是一个 HandlerExecutionChain 对象，其结构如下：

在目标方法之前，执行 Interceptor 的 preHandle 方法

DispatcherServlet#doDispatch

HandlerExecutionChain#applyPreHandle

只要一个拦截器的 preHandle 方法返回 fasle，则执行 triggerAfterCompletion 方法，并返回false，即不会执行目标方法

HandlerExecutionChain#triggerAfterCompletion

HandlerExecutionChain 通过属性 interceptorIndex 记录成功执行多少个拦截器的 preHandle 方法，然后逆序执行 afterCompletion 方法。我们需要注意的是，执行 afterCompletion 方法的时候都加了try...catch，即如果一个拦截器成功执行其 preHandle 方法，后续一定会执行其 afterCompletion 方法