SpringBoot中过滤器、监听器以及拦截器

属于javax.servlet所提供的Api

拦截器原理

简单来讲是通过动态代理实现，被访问的目标方法通过代理类（方法）来执行，这样我们就可以在真正要执行的方法执行前、后做一些处理；
通过拦截器这种方式，使得代码可以进行更高度的抽象。

过滤器初始化、销毁

package com.example.demo.filter;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

/**
 * Created by flyme
 * on 2017/11/6 19:30
 */
@WebFilter(filterName = "myfilter", urlPatterns = "/*")
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) {
        System.out.println("过滤器初始化");
    }

    @Override
    public void destroy() {
        System.out.println("过滤器销毁");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("执行过滤操作");
        filterChain.doFilter(servletRequest, servletResponse);
    }
}

监听器 ServletContex初始化、ServletContex销毁

package com.example.demo.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

/**
 * Created by flyme
 * on 2017/11/6 19:37
 * //
 */
@WebListener
public class MyServletContextListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("ServletContex初始化");
        System.out.println(servletContextEvent.getServletContext().getServerInfo());
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("ServletContex销毁");
    }

}

监听器 ServletContex初始化、Session被创建

package com.example.demo.listener;

import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * Created by flyme
 * on 2017/11/6 19:39
 */
@WebListener
public class MyHttpSessionLister implements HttpSessionListener {
    @Override
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        System.out.println("Session被创建");
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        System.out.println("ServletContex初始化");
    }
}

拦截器

实现自定义拦截器只需要3步：

1、创建我们自己的拦截器类并实现 HandlerInterceptor接口。
2、创建一个Java类继承WebMvcConfigurerAdapter，并重写 addInterceptors 方法。
2、实例化我们自定义的拦截器，然后将对像手动添加到拦截器链中（在addInterceptors方法中添加）

第一个拦截器

package com.example.demo.interceptor;

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

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

/**
 * Created by flyme
 * on 2017/11/6 20:04
 *
 */
public class MyInterceptor1 implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        System.out.println(">>>MyInterceptor1>>>>>>>在请求处理之前进行调用（Controller方法调用之前）");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        System.out.println(">>>MyInterceptor1>>>>>>>请求处理之后进行调用，但是在视图被渲染之前（Controller方法调用之后）");
    }

    @Override
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
        System.out.println(">>>MyInterceptor1>>>>>>>在整个请求结束之后被调用，也就是在DispatcherServlet 渲染了对应的视图之后执行（主要是用于进行资源清理工作）");
    }
}

第二个拦截器

package com.example.demo.interceptor;

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

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

/**
 * Created by flyme
 * on 2017/11/6 20:27
 */
public class MyInterceptor2 implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        System.out.println(">>>MyInterceptor2>>>>>>>在请求处理之前进行调用（Controller方法调用之前）");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        System.out.println(">>>MyInterceptor2>>>>>>>请求处理之后进行调用，但是在视图被渲染之前（Controller方法调用之后）");
    }

    @Override
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
        System.out.println(">>>MyInterceptor2>>>>>>>在整个请求结束之后被调用，也就是在DispatcherServlet 渲染了对应的视图之后执行（主要是用于进行资源清理工作）");
    }
}

将自定义的拦截器手动添加到拦截器链

package com.example.demo;

import com.example.demo.interceptor.MyInterceptor1;
import com.example.demo.interceptor.MyInterceptor2;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

/**
 * Created by flyme
 * on 2017/11/6 20:28
 */
@Configuration
public class MyWebAppConfigurer extends WebMvcConfigurerAdapter {
    public void addInterceptors(InterceptorRegistry registry){
        // 多个拦截器组成一个拦截器链
        // addPathPatterns 用于添加拦截规则
        // excludePathPatterns 用户排除拦截
        registry.addInterceptor(new MyInterceptor1()).addPathPatterns("/**");
        registry.addInterceptor(new MyInterceptor2()).addPathPatterns("/**");
        super.addInterceptors(registry);
    }
}