servlet简介
过滤器，依靠servlet技术。
Java Servlet 是运行在 Web 服务器或应用服务器上的程序，它是作为来自 Web 浏览器或其他 HTTP 客户端的请求和 HTTP 服务器上的数据库或应用程序之间的中间层。
servlet文档：
https://www.runoob.com/servlet/servlet-intro.html
servlet 和tomcat 是什么关系？
过滤器简介
过滤器Filter，是Servlet的的一个实用技术了。可通过过滤器，对请求进行拦截，比如读取session判断用户是否登录、判断访问的请求URL是否有访问权限(黑白名单)等。主要还是可对请求进行预处理。
1.过滤器和拦截器触发时机不一样，过滤器是在请求进入容器后，但请求进入servlet之前进行预处理的。请求结束返回也是，是在servlet处理完后，返回给前端之前。
2.拦截器可以获取IOC容器中的各个bean，而过滤器就不行，因为拦截器是spring提供并管理的，spring的功能可以被拦截器使用，在拦截器里注入一个service，可以调用业务逻辑。而过滤器是JavaEE标准，只需依赖servlet api ，不需要依赖spring。
1 通过@WebFilter来定义filter,
自定义 AllUrlFilter
@Slf4j
@WebFilter(filterName = "allurlfilter", urlPatterns = {"/*"})
public class AllUrlFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
log.info("all url filter -->" + filterConfig.toString());
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
log.info("all url filter do filter");
HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;
System.out.println(request.getHeader("token"));
//往下文传递
filterChain.doFilter(request, response);
}
@Override
public void destroy() {
log.info("all url filter do destroy");
}
}
在springboot 启动器类上加上注解 @ServletComponentScan
@SpringBootApplication
@ServletComponentScan
public class StudySpringbootApplication {
public static void main(String[] args) {
SpringApplication.run(StudySpringbootApplication.class, args);
}
}
总结：
Filter使用白名单过滤Url的方式，配置需要拦截的Url，如果想设置不过滤某些Url需要在doFilter方法中指定。
通过@WebFilter的方式定义Filter，默认使用Filter的类名设置优先级。使用FilterRegistrationBean可以指定优先级
2 filter 中的异常处理
2.1 制造错误
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
log.info("all url filter do filter");
HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;
System.out.println(request.getHeader("token"));
try {
int i = 0 / 0;
} catch (Exception e) {
//错误封装在 request 中
request.setAttribute("errormsg", e.getMessage());
//
request.getRequestDispatcher("/500").forward(request, response);
}
filterChain.doFilter(request, response);
}
尽量使用request.getRequestDispatcher("/500").forward(req, resp);此方式只会在服务器内部转发客户端地址不会发生任何改变；如果使用response.sendRedirect("/500");请求转发，客户端地址会发生改变
2.2 添加/500 url
@GetMapping("/500")
public Response excep401(HttpServletRequest request) throws CustomException {
System.out.println(request.getAttribute("errormsg"));
throw new CustomException();
}
方法2 ： 通过FilterRegistrationBean来定义 多个filter
所有的filter 去掉 @WebFilter
3.1 新建HelloFilter
@Slf4j
//@WebFilter(filterName = "helloFilter" , urlPatterns = {"/hello/*"})
public class HelloFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
log.info("hello filter --> " + filterConfig.toString());
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
log.info("hello do filter");
filterChain.doFilter(servletRequest,servletResponse);
}
@Override
public void destroy() {
log.info("hello do destroy");
}
}
3.2 新建UserFilter
@Slf4j
//@WebFilter(filterName = "userFilter", urlPatterns = {"/user/*"})
public class UserFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
log.info("user filter --> " + filterConfig.toString());
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
log.info("user do filter");
filterChain.doFilter(servletRequest,servletResponse);
}
@Override
public void destroy() {
log.info("user do destroy");
}
}
3.3 新建 FilterConfig 配置
@Configuration
public class FilterConfig {
@Bean
public AllUrlFilter allUrlFilter(){
return new AllUrlFilter();
}
@Bean
public UserFilter userFilter(){
return new UserFilter();
}
@Bean
public HelloFilter helloFilter(){
return new HelloFilter();
}
@Bean
public FilterRegistrationBean filterRegistrationBean(AllUrlFilter allUrlFilter){
FilterRegistrationBean registration = new FilterRegistrationBean();
registration.setFilter(allUrlFilter);
registration.setName("allUrlFilter");
List<String> urlList = new ArrayList<>();
urlList.add("/*");
registration.setUrlPatterns(urlList);
registration.setOrder(1);
return registration;
}
@Bean
public FilterRegistrationBean filterRegistrationBea2(HelloFilter helloFilter){
FilterRegistrationBean registration = new FilterRegistrationBean();
registration.setFilter(helloFilter);
registration.setName("helloFilter");
List<String> urlList = new ArrayList<>();
urlList.add("/hello/*");
registration.setUrlPatterns(urlList);
registration.setOrder(2);
return registration;
}
@Bean
public FilterRegistrationBean filterRegistrationBea3(UserFilter userFilter){
FilterRegistrationBean registration = new FilterRegistrationBean();
registration.setFilter(userFilter);
registration.setName("userFilter");
List<String> urlList = new ArrayList<>();
urlList.add("/user/*");
registration.setUrlPatterns(urlList);
registration.setOrder(3);
return registration;
}
}
SpringBoot中使用Filter和Interceptor
https://juejin.cn/post/6844903869927931918
Spring Interceptor vs Filter
https://juejin.cn/post/6844903828970553358
SpringBoot图文教程6—SpringBoot中过滤器的使用
https://juejin.cn/post/6844904072173060109
