Spring Boot 注册 Servlet 的五种方法

一、Spring Boot 提供了 ServletRegistrationBean, FilterRegistrationBean, ServletListenerRegistrationBean 三个类分别用来注册 Servlet, Filter, Listener

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class RegisterServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        String name = getServletConfig().getInitParameter("name");
        String sex = getServletConfig().getInitParameter("sex");

        resp.getOutputStream().println("name is " + name);
        resp.getOutputStream().println("sex is " + sex);
    }

}

@Bean
public ServletRegistrationBean registerServlet() {
    ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(new RegisterServlet(), "/registerServlet");
    servletRegistrationBean.addInitParameter("name", "javastack");
    servletRegistrationBean.addInitParameter("sex", "man");
    return servletRegistrationBean;
}

二、Servlet 3.0 之前，Servlet、Filter、Listener 这些组件都需要在 web.xml 中进行配置，3.0 之后开始不再需要 web.xml 这个配置文件了，所有的组件都可以通过代码配置或者注解@WebServlet/@WebFilter/@WebListener来达到目的。

import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "javaServlet", urlPatterns = "/javastack.cn", asyncSupported = true,
        initParams = {
        @WebInitParam(name = "name", value = "javastack"),
        @WebInitParam(name = "sex", value = "man") })
public class JavaServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        String name = getServletConfig().getInitParameter("name");
        String sex = getServletConfig().getInitParameter("sex");

        resp.getOutputStream().println("name is " + name);
        resp.getOutputStream().println("sex is " + sex);
    }

}

**注意：**需要在启动类上配置上注解@ServletComponentScan来扫描这三个注解@ServletComponentScan扫描@WebServlet和@WebFilter及@WebListener的配置

三、实现org.springframework.boot.web.servlet.ServletContextInitializer向容器中注入bean的方式动态注册

import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "javaServlet", urlPatterns = "/javastack.cn", asyncSupported = true,
        initParams = {
        @WebInitParam(name = "name", value = "javastack"),
        @WebInitParam(name = "sex", value = "man") })
public class JavaServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        String name = getServletConfig().getInitParameter("name");
        String sex = getServletConfig().getInitParameter("sex");

        resp.getOutputStream().println("name is " + name);
        resp.getOutputStream().println("sex is " + sex);
    }

}

import cn.javastack.springbootbestpractice.servlet.InitServlet;
import org.springframework.boot.web.servlet.ServletContextInitializer;
import org.springframework.stereotype.Component;
import javax.servlet.ServletContext;
import javax.servlet.ServletRegistration;


@Component
public class ServletConfig implements ServletContextInitializer {

    @Override
    public void onStartup(ServletContext servletContext) {
        ServletRegistration initServlet = servletContext.addServlet("initServlet", InitServlet.class);
        initServlet.addMapping("/initServlet");
        initServlet.setInitParameter("name", "javastack");
        initServlet.setInitParameter("sex", "man");
    }

}

四、 使用org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping.registerMapping()方法运行时动态注册

   private void registerServerEndpoint(String path, Object bean) throws NoSuchMethodException {
        RequestMappingHandlerMapping mapping = applicationContext.getBean(RequestMappingHandlerMapping.class);
        RequestMappingInfo.BuilderConfiguration config = new RequestMappingInfo.BuilderConfiguration();

        if (webMvcProperties.getPathmatch().getMatchingStrategy() == WebMvcProperties.MatchingStrategy.PATH_PATTERN_PARSER) {
            config.setPatternParser(new PathPatternParser());
        } else {
            config.setPathMatcher(new AntPathMatcher());
        }
        RequestMappingInfo handleGet = RequestMappingInfo.paths(path).methods(RequestMethod.GET).options(config).build();
        mapping.registerMapping(handleGet, bean, ServletHttpHandler.class.getMethod("handleGet"));

        RequestMappingInfo handlePost = RequestMappingInfo.paths(path).methods(RequestMethod.POST).options(config).build();
        mapping.registerMapping(handlePost, bean, ServletHttpHandler.class.getMethod("handlePost", String.class));
    }

五、使用org.springframework.web.servlet.function.RouterFunction注册

import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.MediaType;
import org.springframework.web.servlet.function.RouterFunction;
import org.springframework.web.servlet.function.RouterFunctions;
import org.springframework.web.servlet.function.ServerRequest;
import org.springframework.web.servlet.function.ServerResponse;

import javax.servlet.ServletException;
import java.io.IOException;
import java.time.Duration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.UUID;

public class StreamServer {
    private final ObjectMapper objectMapper = new ObjectMapper();
    private final String endpoint;
    private final RouterFunction<ServerResponse> router;

    public StreamServer(String endpoint) {
        this.endpoint = endpoint;
        this.router = RouterFunctions.route()
                .POST(this.endpoint, this::handlePost)
                .build();
    }

    public RouterFunction<ServerResponse> getRouter() {
        return this.router;
    }

    private ServerResponse handlePost(ServerRequest request) throws ServletException, IOException {
        List<MediaType> acceptHeaders = request.headers().asHttpHeaders().getAccept();
        if (!acceptHeaders.contains(MediaType.TEXT_EVENT_STREAM)
                || !acceptHeaders.contains(MediaType.APPLICATION_JSON)) {
            return ServerResponse.badRequest()
                    .body("Invalid Accept headers. Expected TEXT_EVENT_STREAM and APPLICATION_JSON");
        }
        String body = request.body(String.class);
        log.info("body:{}", body);
        String sessionId = UUID.randomUUID().toString();

        return ServerResponse.sse(sseBuilder -> {
            sseBuilder.onComplete(() -> {
                log.debug("Request response stream completed for session: {}", sessionId);
            });
            sseBuilder.onTimeout(() -> {
                log.debug("Request response stream timed out for session: {}", sessionId);
            });

            try {
                for (int i = 0; i < 100; ++i) {
                    Map<String, Object> row = new HashMap<>();
                    row.put("rowId", i + 1);
                    row.put("rowName", i + 1);
                    String json = objectMapper.writeValueAsString(row);
                    sseBuilder.id(sessionId)
                            .event("message")
                            .data(json);
                }
                sseBuilder.complete();
            } catch (Exception e) {
                log.error("Failed to handle request stream: {}", e.getMessage());
                sseBuilder.error(e);
            }
        }, Duration.ZERO);
    }
}


import com.github.kylewka.smartai.demo.stream.StreamServer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.function.RouterFunction;
import org.springframework.web.servlet.function.ServerResponse;

@Configuration
public class StreamServerConfig {

    @Bean
    public StreamServer streamServer() {
        return new StreamServer("/test/stream");
    }

    @Bean
    public RouterFunction<ServerResponse> sseRoute(StreamServer streamServer) {
        return streamServer.getRouter();
    }
}

总结：

1\] 参考文章： [https://huanghaoheng.blog.csdn.net/article/details/128703156](https://huanghaoheng.blog.csdn.net/article/details/128703156 "https://huanghaoheng.blog.csdn.net/article/details/128703156") \[2\] 参考文章： [https://cloud.tencent.com/developer/article/1544924](https://cloud.tencent.com/developer/article/1544924 "https://cloud.tencent.com/developer/article/1544924")