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一、前言
在实际开发中，有时候我们可能使用springboot注册web组件，实现某些功能，比如我们需要生成一些api来提供对外的服务，而对应的路径其实是不固定的，那么这种情况下，其实是可以通过这种方式来注册web组件的。

二、如何实现？
1.使用SpringBoot注解加继承HttpServet类实现注册Servlet组件。

@WebServlet("/api")
public class APIServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {log.debug("servlet execute");String servletPath = request.getRequestURI();servletPath = servletPath.substring(apiContext.length() + 2);PrintWriter out = null;try {out = response.getWriter();ResponseDto responseDto = process(servletPath, request, response);out.append(JSON.toJSONString(responseDto));} catch (Exception e) {response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);out.append(JSON.toJSONString(ResponseDto.fail(e.toString())));log.error(e.toString(), e);} finally {if (out != null)out.close();}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {doGet(req, resp);}public ResponseDto process(String path, HttpServletRequest request, HttpServletResponse response) {System.out.println("请求处理");ResponseDto dto = new ResponseDto();return dto;}
}

2.通过继承HttpServet类加配置类来进行注册。

public class APIServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {log.debug("servlet execute");String servletPath = request.getRequestURI();servletPath = servletPath.substring(apiContext.length() + 2);PrintWriter out = null;try {out = response.getWriter();ResponseDto responseDto = process(servletPath, request, response);out.append(JSON.toJSONString(responseDto));} catch (Exception e) {response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);out.append(JSON.toJSONString(ResponseDto.fail(e.toString())));log.error(e.toString(), e);} finally {if (out != null)out.close();}}
}

新建一个配置类，将该Servlet加载到Spring容器中，配置类代码如下：

@Slf4j
@Configuration
public class ServletConfig {@Value("${dbapi.api.context}")String apiContext;@Autowiredprivate APIServlet apiServlet;@Beanpublic ServletRegistrationBean getServletRegistrationBean() {String format = String.format("/%s/*", apiContext);ServletRegistrationBean bean = new ServletRegistrationBean(apiServlet);bean.addUrlMappings(format);log.info("regist APIServlet servelet for {} urlMappings",format);return bean;}
}

两种注册方式都是可用的。

3.注册Filter组件实现过滤。

@Slf4j
@Component
@WebFilter("/api")
public class ApiIPFilter implements Filter {@Autowiredprivate IPService ipService;@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException {log.debug("IP filter execute");HttpServletRequest request = (HttpServletRequest) servletRequest;HttpServletResponse response = (HttpServletResponse) servletResponse;String originIp = IPUtil.getOriginIp(request);String method = request.getMethod();PrintWriter out = null;try {//js跨域的预检请求，不经过处理逻辑。开发模式下，前端启动，访问8521的页面进行请求测试会跨域if (method.equals("OPTIONS")) {response.setStatus(HttpServletResponse.SC_OK);return;}boolean checkIP = ipService.checkIP(originIp);if (!checkIP) {out = response.getWriter();response.setStatus(HttpServletResponse.SC_FORBIDDEN);out.append(JSON.toJSONString(ResponseDto.fail("Illegal ip (" + originIp + "), access forbidden")));} else {filterChain.doFilter(servletRequest, servletResponse);}} catch (Exception e) {response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);out.append(JSON.toJSONString(ResponseDto.fail(e.toString())));log.error(e.toString());} finally {if (out != null) {out.close();}}}

这里会对某些IP进行过滤。

最后启动类中的@ServletComponentScan注解扫描web组件。

@SpringBootApplication
//SpringBoot启动时扫描注册注解标注的Web组件
@ServletComponentScan
public class SpringbootDemoApplication {public static void main(String[] args) {SpringApplication.run(SpringbootDemoApplication.class, args);}
}