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）
- 使用spring boot提供的FilterRegistrationBean注册Filter
- 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<<<<<<<");
}原文地址：https://blog.csdn.net/m0_46616045/article/details/128823964
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