chain.doFilter(request, response);這個方法的調(diào)用作為分水嶺。事實(shí)上調(diào)用Servlet的doService()方法是在這個方法中進(jìn)行的。

@WebFilter(urlPatterns = "/*", filterName = "myFilter")
public class MyFilter implements Filter {
    
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // 初始化代碼
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, 
                         FilterChain chain) throws IOException, ServletException {
        // 前置處理
        System.out.println("Before Filter");
        
        // 執(zhí)行后續(xù)過濾器或Servlet
        chain.doFilter(request, response);
        
        // 后置處理
        System.out.println("After Filter");
    }

    @Override
    public void destroy() {
        // 銷毀代碼
    }
}

<filter>
      <filter-name>filterDemo1</filter-name>
      <filter-class>com.thit.filters.Filter1</filter-class>
  </filter>
  <filter-mapping>
      <filter-name>filterDemo1</filter-name>
      <url-pattern>/*</url-pattern>
      <!-- /*是對所有的文件進(jìn)行攔截 -->
  </filter-mapping>

//攔截器1
public class LoginInterceptor implements HandlerInterceptor{
	
 
	//預(yù)處理1.程序先執(zhí)行preHandle()方法，如果該方法的返回值為true，則程序會繼續(xù)向下執(zhí)行處理器中的方法，否則將不再向下執(zhí)行。
	public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
		// TODO Auto-generated method stub
		System.out.println("1:攔截器1,程序進(jìn)入preHandle方法");
		User u=(User) request.getSession().getAttribute("user");
		if(u==null) {
			System.out.println("在進(jìn)入方法之前判斷session的用戶是否為空！");
			System.out.println("地址："+request.getContextPath());
			//http://localhost:8080/login
			response.sendRedirect(request.getContextPath()+"/login");
			return false;
		}
 
		return true;
	}
	//后處理 	2.在業(yè)務(wù)處理器（即控制器Controller類）處理完請求后，會執(zhí)行postHandle()方法，然后會通過DispatcherServlet向客戶端返回響應(yīng)。
 
	public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
			ModelAndView modelAndView) throws Exception {
		// TODO Auto-generated method stub
		System.out.println("2:攔截器1,程序進(jìn)入postHandle方法");
		
	}
	//完工之后 	3.在DispatcherServlet處理完請求后，才會執(zhí)行afterCompletion()方法。
	public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
			throws Exception {
		// TODO Auto-generated method stub
		System.out.println("3:攔截器1,程序進(jìn)入afterCompletion方法");
		
	}
 
}

@Configuration
public class WebConfig implements WebMvcConfigurer {
    
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new MyInterceptor())
                .addPathPatterns("/**")  // 攔截所有路徑
                .excludePathPatterns("/login"); // 排除登錄路徑
        
        // 可以添加多個攔截器
        registry.addInterceptor(new AnotherInterceptor())
                .addPathPatterns("/admin/**");
    }
}

<mvc:interceptors>
    <mvc:interceptor>
        <mvc:mapping path="/**"/>
        <mvc:exclude-mapping path="/login"/>
        <bean class="com.example.MyInterceptor"/>
    </mvc:interceptor>
</mvc:interceptors>