基于Springboot搭建java项目（二十三）——SpringBoot使用过滤器拦截器和监听器

Posted 2023-03-04 dreamer_0423

SpringBoot使用过滤器、拦截器和监听器

一、SpringBoot使用过滤器

Spring boot过滤器的使用（两种方式）

1. 使用spring boot提供的FilterRegistrationBean注册Filter
2. 使用原生servlet注解定义Filter

两种方式的本质都是一样的，都是去FilterRegistrationBean注册自定义Filter

方式一：

第一步：先定义Filter。

import javax.servlet.*;
import java.io.IOException;
public class MyFilter implements Filter 
    @Override
    public void init(FilterConfig filterConfig) throws ServletException 
    
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException 
        // do something 处理request 或response
        System.out.println("filter1");
        // 调用filter链中的下一个filter
        filterChain.doFilter(servletRequest,servletResponse);
    
    @Override
    public void destroy() 
    

第二步：注册自定义Filter

@Configuration
public class FilterConfig 
    @Bean
    public FilterRegistrationBean registrationBean() 
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(new MyFilter());
        filterRegistrationBean.addUrlPatterns("/*");
        filterRegistrationBean.setOrder(1);//定义过滤器的执行先后顺序  值越小越先执行 不影响Bean的加载顺序
        return filterRegistrationBean;
    

方式二：

// 注入spring容器
@Order(1)//定义过滤器的执行先后顺序  值越小越先执行 不影响Bean的加载顺序
@Component
// 定义filterName 和过滤的url
@WebFilter(filterName = "my2Filter" ,urlPatterns = "/*")
public class My2Filter implements Filter 
    @Override
    public void init(FilterConfig filterConfig) throws ServletException 
    
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException 
        System.out.println("filter2");
    
    @Override
    public void destroy() 
    

二、SpringBoot使用拦截器

第一步：定义拦截器

public class MyInterceptor 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, @Nullable ModelAndView modelAndView) throws Exception 
        System.out.println("postHandle");
    
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception 
        System.out.println("afterCompletion");
    

第二步：配置拦截器

@Configuration
public class InterceptorConfig implements WebMvcConfigurer 
    @Override
    public void addInterceptors(InterceptorRegistry registry) 
        registry.addInterceptor(new MyInterceptor());
    

三、过滤器和拦截器的执行顺序

过滤器的执行顺序是安装@Order注解中的值，或者是setOrder()中值的进行执行顺序排序的，值越小就越靠前。

拦截器则是先声明的拦截器 preHandle() 方法先执行，而postHandle()方法反而会后执行。也即是：postHandle() 方法被调用的顺序跟 preHandle() 居然是相反的。如果实际开发中严格要求执行顺序，那就需要特别注意这一点。

四、SpringBoot使用监听器

1、统计网站最多在线人数监听器的例子

/**
 * 上下文监听器，在服务器启动时初始化onLineCount和maxOnLineCount两个变量，
 * 并将其置于服务器上下文（ServletContext）中，其初始值都是0。
 */
@WebListener
public class InitListener implements ServletContextListener 
    public void contextDestroyed(ServletContextEvent evt) 
    
    public void contextInitialized(ServletContextEvent evt) 
        evt.getServletContext().setAttribute("onLineCount", 0);
        evt.getServletContext().setAttribute("maxOnLineCount", 0);
    

/**
 * 会话监听器，在用户会话创建和销毁的时候根据情况修改onLineCount和maxOnLineCount的值。
 */
@WebListener
public class MaxCountListener implements HttpSessionListener 
    public void sessionCreated(HttpSessionEvent event) 
        ServletContext ctx = event.getSession().getServletContext();
        int count = Integer.parseInt(ctx.getAttribute("onLineCount").toString());
        count++;
        ctx.setAttribute("onLineCount", count);
        int maxOnLineCount = Integer.parseInt(ctx.getAttribute("maxOnLineCount").toString());
        if (count > maxOnLineCount) 
            ctx.setAttribute("maxOnLineCount", count);
            DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            ctx.setAttribute("date", df.format(new Date()));
        
    
    public void sessionDestroyed(HttpSessionEvent event) 
        ServletContext app = event.getSession().getServletContext();
        int count = Integer.parseInt(app.getAttribute("onLineCount").toString());
        count--;
        app.setAttribute("onLineCount", count);
    

新建一个servlet处理

@WebServlet(name = "SessionServlet",value = "/sessionCount")
public class SessionServlet extends HttpServlet 
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException 
        resp.setContentType("text/html");
        //获取上下文对象
        ServletContext servletContext = this.getServletContext();
        Integer onLineCount = (Integer) servletContext.getAttribute("onLineCount");
        System.out.println("invoke doGet");
        PrintWriter out = resp.getWriter();
        out.println("<html><body>");
        out.println("<h1>" + onLineCount + "</h1>");
        out.println("</body></html>");
    

2、springboot监听器的使用（以实现异步Event监听为例子）

定义事件类 Event

创建一个类，继承ApplicationEvent，并重写构造函数。ApplicationEvent是Spring提供的所有应用程序事件扩展类。

public class Event extends ApplicationEvent 
    private static final long serialVersionUID = 1L;
    private String msg ;
    private static final Logger logger=LoggerFactory.getLogger(Event.class);
    public Event(String msg) 
        super(msg);
        this.msg = msg;
        logger.info("add event success! message: ", msg);
    
    public String getMsg() 
        return msg;
    
    public void setMsg(String msg) 
        this.msg = msg;
    

创建一个用于监听指定事件的类，需要实现ApplicationListener接口，说明它是一个应用程序事件的监听类。注意这里需要加上@Component注解，将其注入Spring容器中。

@Component
public class MyListener implements ApplicationListener<Event>
    private static final Logger logger= LoggerFactory.getLogger(MyListener.class);
    @Override
    public void onApplicationEvent(Event event) 
        logger.info("listener get event,sleep 2 second...");
        try 
            Thread.sleep(2000);
         catch (InterruptedException e) 
            e.printStackTrace();
        
        logger.info("event msg is:",event.getMsg());
    

事件发布
事件发布很简单，只需要使用Spring 提供的ApplicationEventPublisher来发布自定义事件

@Autowired 注入ApplicationEventPublisher

 @RequestMapping("/notice/msg")
    public void notice(@PathVariable String msg)
        logger.info("begin>>>>>");
        applicationEventPublisher.publishEvent(new Event(msg));
        logger.info("end<<<<<<<");