记一次Springboot启动异常

　　启动Springboot项目报以下异常：

　　

org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.context.ApplicationContextException: Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean.
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:155) ~[spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:544) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at hello.Application.main(Application.java:13) [classes/:na]
Caused by: org.springframework.context.ApplicationContextException: Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean.
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.getWebServerFactory(ServletWebServerApplicationContext.java:204) ~[spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:178) ~[spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:152) ~[spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    ... 8 common frames omitte

　　很明显是提示Application无法获取ServletWebServerFactory实例，首先要注意， 由于Springboot在以往使用Spring都要配置下提供了集成方案，所以最简单的方法就是采用默认的配置，解决方法非常简单，只需在你的启动类中加入@EnableAutoConfiguration，当然你也可以手动配置，如下为自动配置。

package hello;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;

import java.util.Arrays;
@EnableAutoConfiguration
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public CommandLineRunner commandLineRunner(ApplicationContext ctx) {
        return args -> {

            System.out.println("Let's inspect the beans provided by Spring Boot:");

            String[] beanNames = ctx.getBeanDefinitionNames();
            Arrays.sort(beanNames);
            for (String beanName : beanNames) {
                System.out.println(beanName);
            }

        };
    }
}

　　手动配置请参考官网，地址：https://docs.spring.io/spring-boot/docs/2.0.1.BUILD-SNAPSHOT/reference/html/howto-embedded-web-servers.html#howto-configure-tomcat

　　下面配一个全部手动配置的代码，其中@value标签的内容需要自己写properties文件：

package com.gws.configuration;

import org.apache.catalina.connector.Connector;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.web.embedded.tomcat.TomcatConnectorCustomizer;
import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
import org.springframework.boot.web.servlet.MultipartConfigFactory;
import org.springframework.boot.web.servlet.server.ServletWebServerFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.servlet.MultipartConfigElement;


/**
 * 使用tomcat配置
 *
 * @version 
 * @author 
 * 
 */
@Configuration
public class TomcatConfig {

    @Value("${spring.server.port}")
    private String port;
    @Value("${spring.server.acceptorThreadCount}")
    private String acceptorThreadCount;
    @Value("${spring.server.minSpareThreads}")
    private String minSpareThreads;
    @Value("${spring.server.maxSpareThreads}")
    private String maxSpareThreads;
    @Value("${spring.server.maxThreads}")
    private String maxThreads;
    @Value("${spring.server.maxConnections}")
    private String maxConnections;
    @Value("${spring.server.protocol}")
    private String protocol;
    @Value("${spring.server.redirectPort}")
    private String redirectPort;
    @Value("${spring.server.compression}")
    private String compression;
    @Value("${spring.server.connectionTimeout}")
    private String connectionTimeout;

    @Value("${spring.server.MaxFileSize}")
    private String MaxFileSize;
    @Value("${spring.server.MaxRequestSize}")
    private String MaxRequestSize;

    @Bean
    public ServletWebServerFactory servletContainer() {
        TomcatServletWebServerFactory tomcat = new TomcatServletWebServerFactory();
        tomcat.addConnectorCustomizers(new GwsTomcatConnectionCustomizer());
        return tomcat;
    }

    @Bean
    public MultipartConfigElement multipartConfigElement() {
        MultipartConfigFactory factory = new MultipartConfigFactory();
        //  单个数据大小
        factory.setMaxFileSize(MaxFileSize); // KB,MB
        /// 总上传数据大小
        factory.setMaxRequestSize(MaxRequestSize);
        return factory.createMultipartConfig();
    }

    /**
     *
     * 默认http连接
     *
     * @version
     * @author liuyi  2016年7月20日 下午7:59:41
     *
     */
    public class GwsTomcatConnectionCustomizer implements TomcatConnectorCustomizer {

        public GwsTomcatConnectionCustomizer() {
        }

        @Override
        public void customize(Connector connector) {
            connector.setPort(Integer.valueOf(port));
            connector.setAttribute("connectionTimeout", connectionTimeout);
            connector.setAttribute("acceptorThreadCount", acceptorThreadCount);
            connector.setAttribute("minSpareThreads", minSpareThreads);
            connector.setAttribute("maxSpareThreads", maxSpareThreads);
            connector.setAttribute("maxThreads", maxThreads);
            connector.setAttribute("maxConnections", maxConnections);
            connector.setAttribute("protocol", protocol);
            connector.setAttribute("redirectPort", "redirectPort");
            connector.setAttribute("compression", "compression");
        }
    }
}