SpringBoot 2.x （7）：拦截器

 类似以前SpringMVC的拦截器，但也有一些区别

SpringBoot的拦截器有两种方式：

第一种方式：过时的方式，适用于SpringBoot1.x的方式

package org.dreamtech.springboot.interceptor;

import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@SuppressWarnings("deprecation")
public class CustomWebMvcConfigurer extends WebMvcConfigurerAdapter {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoginIntercepter()).addPathPatterns("/test/*/**");
        super.addInterceptors(registry);
    }
}

第二种方式：基于Java8与Spring5的方式

原理：在WebMvcConfigurer接口中定义了默认方法，利用Java8新特性：接口中可以写方法

package org.dreamtech.springboot.interceptor;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class CustomWebMvcConfigurer implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoginInterceptor()).addPathPatterns("/login/*/**");
        WebMvcConfigurer.super.addInterceptors(registry);
    }
}

LoginInterceptor：只是实现了三个基本方法，分别打印一句话，了解执行顺序：

package org.dreamtech.springboot.interceptor;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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

public class LoginInterceptor implements HandlerInterceptor {
    /**
     * 拦截之前调用（进入Controller之前）
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        System.out.println("[ preHandle LoginInterceptor ]");
        return HandlerInterceptor.super.preHandle(request, response, handler);
    }

    /**
     * 调用方法之后，视图渲染之前
     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
            ModelAndView modelAndView) throws Exception {
        System.out.println("[ postHandle LoginInterceptor ]");
        HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);
    }

    /**
     * 完成拦截之后，用于清理资源
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
        System.out.println("[ afterCompletion LoginInterceptor ]");
        HandlerInterceptor.super.afterCompletion(request, response, handler, ex);
    }
}

Controller:

package org.dreamtech.springboot.controller;

import java.util.HashMap;
import java.util.Map;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class DemoController {

    @RequestMapping("/login/account")
    private Object account() {
        Map<String, Object> modelMap = new HashMap<String, Object>();
        modelMap.put("money", 1000);
        System.out.println("[ account DemoController ]");
        return modelMap;
    }
}

访问localhost:8080/login/account打印情况如下：

[ preHandle LoginInterceptor ]
[ account DemoController ]
[ postHandle LoginInterceptor ]
[ afterCompletion LoginInterceptor ]

如果没有以上打印，要注意这几点：

1.是否有@Configuration注解

2.是否将拦截路径写成/xxx/*/**，如果是/xxx/*/*就会拦截失败

同样地，我们可以添加多个拦截器

        registry.addInterceptor(new LoginInterceptor()).addPathPatterns("/login/*/**");
        registry.addInterceptor(new TestInterceptor()).addPathPatterns("/test/*/**");
        registry.addInterceptor(new DemoInterceptor()).addPathPatterns("/demo/*/**");

或者链式调用：拦截所有路径，但不包括/login

registry.addInterceptor(new MyInterceptor()).addPathPatterns("/**").excludePathPatterns("/login");

多个拦截器的调用顺序：可以理解为包裹的方式

package org.dreamtech.springboot.interceptor;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class CustomWebMvcConfigurer implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoginInterceptor()).addPathPatterns("/login/*/**");
        registry.addInterceptor(new DemoInterceptor()).addPathPatterns("/login/*/**");
        WebMvcConfigurer.super.addInterceptors(registry);
    }
}

DemoInterceptor和LoginInterceptor内容基本一致

最终的打印：

[ preHandle LoginInterceptor ]
[ preHandle DemoInterceptor ]
[ account DemoController ]
[ postHandle DemoInterceptor ]
[ postHandle LoginInterceptor ]
[ afterCompletion DemoInterceptor ]
[ afterCompletion LoginInterceptor ]

最后：

Filter和Interceptor的区别：

1.Filter基于Servlet，而Interceptor不依赖于Servlet容器

2.Filter只在容器被初始化的时候被调用一次，Interceptor次数没有限制

3.Interceptor基于AOP思想，Filter基于doFilter方法

两者的执行顺序：

过滤前->拦截前->Controller->拦截后->过滤后