SpringMVC第六天(拦截器)

概念

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

作用：

在指定的方法调用前后执行预先设定的代码

阻止原始方法的执行

拦截器与过滤器的区别

归属不同：Filter属于Servlet技术，Interceptor属于SpringMVC技术

拦截内容不同：Filter对所有访问进行增强，Interceptor仅针对SpringMVC的访问进行技术增强

示例

第一步、声明拦截器的Bean，并实现HandlerInterceptor接口

package com.cacb.controller.interceptor;


import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.ws.handler.Handler;

@Component
public class ProjectInterceptor  implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("preHandle");
        return true;
    }

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

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

第二步、定义配置类，继承WebMvcConfigurationSuport，实现addInterceptor方法

@Configuration
public class SpringMvcSupport extends WebMvcConfigurationSupport {
    @Autowired
    private ProjectInterceptor projectInterceptor;


    @Override
    protected void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(projectInterceptor).addPathPatterns("/books");
    }
}

第三步、添加拦截器并设定拦截的访问路径，路径可以通过可变参数设置多个

@Configuration
public class SpringMvcSupport extends WebMvcConfigurationSupport {
    @Autowired
    private ProjectInterceptor projectInterceptor;


    @Override
    protected void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(projectInterceptor).addPathPatterns("/books");
    }
}

第四步(可选)使用标准接口WebMvcConfigurer简化开发（取代support文件）

@Configuration
@ComponentScan("com.cacb.controller")
@EnableWebMvc

public class SpringMvcConfig  implements WebMvcConfigurer {
    
    @Autowired
    ProjectInterceptor projectInterceptor;
    
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(projectInterceptor).addPathPatterns("/books");
    }
}

拦截器执行顺序：

拦截器参数

前置处理

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

参数

request：请求对象

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

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对象进行了再包装

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

modelAndView：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