详解SpringMVC的拦截器参数及拦截器链配置-Java开发

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

一、拦截器参数

前置处理

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

参数：

■ request：请求对象

■ response：响应对象

■ handler：被调用的处理器对象，本质上是一个方法对象，对反射技术中的Method对象进行再包装

返回值：

■ 返回值为false，被拦截的处理器将不执行

后置处理

public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle...");
    }

参数：

modeAanView：如果处理器执行完成具有返回结果，可以读取到对应数据与页面信息，并进行调整

完成后处理

public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("afterCompletion...");
    }

参数：

ex：如果处理器执行过程中出现异常对象，可以针对异常情况进行单独处理

二、拦截器链配置

配置第一个拦截器

@Component
//定义拦截器类，实现HandlerInterceptor接口
//注意当前类必须受Spring容器控制
public class ProjectInterceptor implements HandlerInterceptor {
    @Override
    //原始方法调用前执行的内容
    //返回值类型可以拦截控制的执行，true放行，false终止
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String contentType = request.getHeader("Content-Type");
        HandlerMethod hm = (HandlerMethod)handler;
        System.out.println("preHandle..."+contentType);
        return true;
    }
 
    @Override
    //原始方法调用后执行的内容
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle...");
    }
 
    @Override
    //原始方法调用完成后执行的内容
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("afterCompletion...");
    }
}

配置第二个拦截器

@Component
public class ProjectInterceptor2 implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("preHandle...222");
        return true;
    }
 
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle...222");
    }
 
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("afterCompletion...222");
    }
}

当配置多个拦截器时，形成拦截器链

@Configuration
@ComponentScan({"com.itheima.controller"})
@EnableWebMvc
//实现WebMvcConfigurer接口可以简化开发，但具有一定的侵入性
public class SpringMvcConfig implements WebMvcConfigurer {
    @Autowired
    private ProjectInterceptor projectInterceptor;
    @Autowired
    private ProjectInterceptor2 projectInterceptor2;
 
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        //配置多拦截器
        registry.addInterceptor(projectInterceptor).addPathPatterns("/books","/books/*");
        registry.addInterceptor(projectInterceptor2).addPathPatterns("/books","/books/*");
    }
}

三个拦截器构成的拦截器链图例