原文地址：https://wyiyi.github.io/amber/2022/12/01/filter-note/
一、@WebFilter
Filter 上加 @WebFilter (javax.servlet.annotation.WebFilter)，指定 value，启动类加 @ServletComponentScan
【注意】：@ServletComponentScan 这个注解仅对内嵌的 tomcat 生效，如果使用单独的 tomcat，这种方式无效。
示例一：
@WebFilter(filterName = "aFilter", value = "/api/amber/*")
public class AFilter implements Filter {
private static final Logger LOGGER = LoggerFactory.getLogger(AFilter.class);
@Autowired
private UserService userService;
@Override
public void init(FilterConfig filterConfig) {
LOGGER.info("A Filter初始化,只初始化一次...");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
LOGGER.info("AFilter 处理中...");
User user = userService.getUserInfo();
LOGGER.info("USER 信息：" + user);
HttpServletRequest servletRequest = (HttpServletRequest) request;
LOGGER.info(String.valueOf(servletRequest.getRequestURL()));
chain.doFilter(request, response);
}
@Override
public void destroy() {
LOGGER.info("A Filter销毁...");
}
}示例二：
@SpringBootApplication
@ServletComponentScan
@MapperScan({"com.amber.common.dao"})
public class BronzeApplication {
public static void main(String[] args) {
SpringApplication.run(BronzeApplication.class, args);
}
}示例三：
2022-12-01 12:28:38.785 INFO 7052 --- [ main] com.amber.common.filter.AFilter : A Filter初始化,只初始化一次...
2022-12-01 12:28:39.827 INFO 7052 --- [ main] com.amber.common.BronzeApplication : Started BronzeApplication in 2.267 seconds (JVM running for 2.808)
2022-12-01 12:28:44.342 INFO 7052 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2022-12-01 12:28:44.342 INFO 7052 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2022-12-01 12:28:44.345 INFO 7052 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 3 ms
2022-12-01 12:28:44.350 INFO 7052 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : AFilter 处理中...
2022-12-01 12:28:44.350 INFO 7052 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : USER 信息：User(screen_name=amber, text=今天星期四, created_at=Thu Dec 01 12:28:44 CST 2022)
2022-12-01 12:28:44.350 INFO 7052 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : http://localhost:8080/api/amber/weibo可以看到输出日志是正确的。
二、@Component + FilterRegistrationBean
在 Filter 上加 @Component ，通过 FilterRegistrationBean addUrlPatterns 进行实例注册。
示例一：
@Component
public class AFilter implements Filter {
private static final Logger LOGGER = LoggerFactory.getLogger(AFilter.class);
@Autowired
private UserService userService;
@Override
public void init(FilterConfig filterConfig) {
LOGGER.info("A Filter初始化,只初始化一次...");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
LOGGER.info("AFilter 处理中...");
User user = userService.getUserInfo();
LOGGER.info("USER 信息：" + user);
HttpServletRequest servletRequest = (HttpServletRequest) request;
LOGGER.info(String.valueOf(servletRequest.getRequestURL()));
chain.doFilter(request, response);
}
@Override
public void destroy() {
LOGGER.info("A Filter销毁...");
}
}示例二：
@Configuration
public class ComponentFilterOrderConfig {
@Bean
public FilterRegistrationBean filterBeanOne(AFilter aFilter) {
FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
filterRegistrationBean.setFilter(aFilter);
filterRegistrationBean.addUrlPatterns("/api/amber/*");
filterRegistrationBean.setName("aFilter");
return filterRegistrationBean;
}
}示例三：
2022-12-01 12:34:48.366 INFO 16188 --- [ main] com.amber.common.filter.AFilter : A Filter初始化,只初始化一次...
2022-12-01 12:34:49.458 INFO 16188 --- [ main] com.amber.common.BronzeApplication : Started BronzeApplication in 2.283 seconds (JVM running for 2.816)
2022-12-01 12:34:54.176 INFO 16188 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2022-12-01 12:34:54.176 INFO 16188 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2022-12-01 12:34:54.180 INFO 16188 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 4 ms
2022-12-01 12:34:54.184 INFO 16188 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : AFilter 处理中...
2022-12-01 12:34:54.184 INFO 16188 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : USER 信息：User(screen_name=amber, text=今天星期四, created_at=Thu Dec 01 12:34:54 CST 2022)
2022-12-01 12:34:54.184 INFO 16188 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : http://localhost:8080/api/amber/weibo可以看到输出日志是正确的。
三、前方高能：@WebFilter + @Component 同时使用
切莫 @WebFilter 指定 value 后又加 @Component，会注册两个 filter，导致走两次
示例一：
@Component
@WebFilter(filterName = "aFilter", value = "/api/amber/*")
public class AFilter implements Filter {
private static final Logger LOGGER = LoggerFactory.getLogger(AFilter.class);
@Autowired
private UserService userService;
@Override
public void init(FilterConfig filterConfig) {
LOGGER.info("A Filter初始化,只初始化一次...");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
LOGGER.info("AFilter 处理中...");
User user = userService.getUserInfo();
LOGGER.info("USER 信息：" + user);
HttpServletRequest servletRequest = (HttpServletRequest) request;
LOGGER.info(String.valueOf(servletRequest.getRequestURL()));
chain.doFilter(request, response);
}
@Override
public void destroy() {
LOGGER.info("A Filter销毁...");
}
}示例二：
2022-12-01 12:38:27.535 INFO 21136 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 831 ms
2022-12-01 12:38:27.557 DEBUG 21136 --- [ main] o.s.b.w.s.ServletContextInitializerBeans : Mapping filters: aFilter urls=[/api/amber/*] order=2147483647, characterEncodingFilter urls=[/*] order=-2147483648, formContentFilter urls=[/*] order=-9900, requestContextFilter urls=[/*] order=-105, AFilter urls=[/*] order=2147483647
2022-12-01 12:38:27.557 DEBUG 21136 --- [ main] o.s.b.w.s.ServletContextInitializerBeans : Mapping servlets: dispatcherServlet urls=[/]
2022-12-01 12:38:27.568 DEBUG 21136 --- [ main] o.s.b.w.s.f.OrderedRequestContextFilter : Filter 'requestContextFilter' configured for use
2022-12-01 12:38:27.568 INFO 21136 --- [ main] com.amber.common.filter.AFilter : A Filter初始化,只初始化一次...
2022-12-01 12:38:27.568 DEBUG 21136 --- [ main] s.b.w.s.f.OrderedCharacterEncodingFilter : Filter 'characterEncodingFilter' configured for use
2022-12-01 12:38:27.568 INFO 21136 --- [ main] com.amber.common.filter.AFilter : A Filter初始化,只初始化一次...
2022-12-01 12:38:27.568 DEBUG 21136 --- [ main] o.s.b.w.s.f.OrderedFormContentFilter : Filter 'formContentFilter' configured for use
2022-12-01 12:38:27.637 INFO 21136 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting...
2022-12-01 12:38:27.782 INFO 21136 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Start completed.
2022-12-01 12:38:28.654 INFO 21136 --- [ main] com.amber.common.BronzeApplication : Started BronzeApplication in 2.223 seconds (JVM running for 2.775)
2022-12-01 12:38:45.133 INFO 21136 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2022-12-01 12:38:45.133 INFO 21136 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2022-12-01 12:38:45.138 INFO 21136 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 5 ms
2022-12-01 12:38:45.143 INFO 21136 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : AFilter 处理中...
2022-12-01 12:38:45.143 INFO 21136 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : USER 信息：User(screen_name=amber, text=今天星期四, created_at=Thu Dec 01 12:38:45 CST 2022)
2022-12-01 12:38:45.143 INFO 21136 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : http://localhost:8080/api/amber/weibo
2022-12-01 12:38:45.144 INFO 21136 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : AFilter 处理中...
2022-12-01 12:38:45.144 INFO 21136 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : USER 信息：User(screen_name=amber, text=今天星期四, created_at=Thu Dec 01 12:38:45 CST 2022)
2022-12-01 12:38:45.144 INFO 21136 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : http://localhost:8080/api/amber/weibo可以看到输出日志已经不是期望的结果，发现：
- AFilter init() 初始化 两次
- AFilter doFilter() 处理中 两次
在 ApplicationFilterChain Debug 中发现注册了两个 Filter 分别是：AFilter 和 aFilter，导致走两次。
@WebFilter + @Component 同时使用需注意
两个方法全部都一起用是没问题的，会覆盖，切忌的是，
只用 @WebFilter + @Component，不用 @ServletComponentScan 和 FilterRegistrationBean，
这时如果 webFilter 配置的是非全局的过滤器，就会被 @Component 注解再注册一个全局的过滤器了。
其中：
- 当访问的 url 为
/index/*或者/product/*的时候，该过滤器也执行了！也就是说，WebFilter 注解配置的 urlPatterns 没有起作用。【注意】：@WebFilter 中的 value 属性等价于 urlPatterns 属性，但是两个不应该同时使用。 @WebFilter(filterName = "aFilter", value = "/api/amber/*")中的 value（或者 urlPatterns）属性，
也可以通过 @Component + FilterRegistrationBean 进行实例注册方式：filterRegistrationBean.addUrlPatterns("/*");解决。
小插曲：
当浏览器访问 http://localhost:8080/index 发现日志输出了两次， doFilter() 方法执行了两次。
示例一：
@WebFilter(filterName = "aFilter", value = "/*")
public class AFilter implements Filter {
private static final Logger LOGGER = LoggerFactory.getLogger(AFilter.class);
@Autowired
private UserService userService;
@Override
public void init(FilterConfig filterConfig) {
LOGGER.info("A Filter初始化,只初始化一次...");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
LOGGER.info("AFilter 处理中...");
User user = userService.getUserInfo();
LOGGER.info("USER 信息：" + user);
}
@Override
public void destroy() {
LOGGER.info("A Filter销毁...");
}
}示例二：
2022-11-30 23:55:43.928 INFO 22280 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 795 ms
2022-11-30 23:55:43.952 INFO 22280 --- [ main] com.amber.common.filter.AFilter : A Filter初始化,只初始化一次...
2022-11-30 23:55:44.022 INFO 22280 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting...
2022-11-30 23:55:44.170 INFO 22280 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Start completed.
2022-11-30 23:56:03.418 INFO 22280 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2022-11-30 23:56:03.418 INFO 22280 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2022-11-30 23:56:03.423 INFO 22280 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 5 ms
2022-11-30 23:56:03.431 INFO 22280 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : AFilter 处理中...
2022-11-30 23:56:03.431 INFO 22280 --- [nio-8080-exec-1] com.amber.common.filter.AFilter : USER 信息：User(screen_name=amber, text=今天星期三, created_at=Wed Nov 30 23:56:03 CST 2022)
2022-11-30 23:56:03.455 INFO 22280 --- [nio-8080-exec-6] com.amber.common.filter.AFilter : AFilter 处理中...
2022-11-30 23:56:03.456 INFO 22280 --- [nio-8080-exec-6] com.amber.common.filter.AFilter : USER 信息：User(screen_name=amber, text=今天星期三, created_at=Wed Nov 30 23:56:03 CST 2022)x打开 Network 发现实际的网络请求有两个：
/index—— 实际请求/favicon.ico——浏览器展示tab上的网站图标。
示例三：
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
LOGGER.info("AFilter 处理中...");
User user = userService.getUserInfo();
LOGGER.info("USER 信息：" + user);
HttpServletRequest servletRequest = (HttpServletRequest) request;
LOGGER.info(servletRequest.getRequestURI());
}通过 doFilter() 方法中获取 HttpServletRequest 的 getRequestURI() 方法 中发现有 /favicon.ico 请求。
示例四：
2022-12-01 00:11:11.428 INFO 13616 --- [nio-8080-exec-2] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2022-12-01 00:11:11.428 INFO 13616 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2022-12-01 00:11:11.431 INFO 13616 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet : Completed initialization in 3 ms
2022-12-01 00:11:11.436 INFO 13616 --- [nio-8080-exec-2] com.amber.common.filter.AFilter : AFilter 处理中...
2022-12-01 00:11:11.436 INFO 13616 --- [nio-8080-exec-2] com.amber.common.filter.AFilter : USER 信息：User(screen_name=amber, text=今天星期三, created_at=Thu Dec 01 00:11:11 CST 2022)
2022-12-01 00:11:11.436 INFO 13616 --- [nio-8080-exec-2] com.amber.common.filter.AFilter : /index
2022-12-01 00:11:11.449 INFO 13616 --- [nio-8080-exec-6] com.amber.common.filter.AFilter : AFilter 处理中...
2022-12-01 00:11:11.449 INFO 13616 --- [nio-8080-exec-6] com.amber.common.filter.AFilter : USER 信息：User(screen_name=amber, text=今天星期三, created_at=Thu Dec 01 00:11:11 CST 2022)
2022-12-01 00:11:11.450 INFO 13616 --- [nio-8080-exec-6] com.amber.common.filter.AFilter : /favicon.ico小插曲是因为浏览器会自动发一个获取网站图标的请求，而过滤器配置的是全局过滤器，所以就会走两次。
留言
