spring boot启动找不到ServletWebServer

问题描述

spring boot项目需要打包为war包，按照官网的操作：

1. 启动类继承SpringBootServletInitializer类
2. maven的pom文件将自带的tomcat设置为provided(这个的意思就是：被依赖项目理论上可以参与编译、测试、运行等阶段，相当于compile，但是再打包阶段做了exclude的动作)

public class AasWebApplication extends SpringBootServletInitializer {

   @Override
   protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
      return application.sources(AasWebApplication.class);
   }

   static {
      HttpsURLConnection.setDefaultHostnameVerifier((hostname, session) -> true);
   }

   public static void main(String[] args){
      SpringApplication.run(AasWebApplication.class,args);
   }
}

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <scope>provided</scope>
</dependency>

在做了这两个操作之后，打包成war包是没有问题，但是本地运行spring boot项目的时候报错了，最主要的错误信息是：Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean

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)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:540)
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775)
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:316)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248)
    at com.xc.AasWebApplication.main(AasWebApplication.java:33)
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)
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:178)
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:152)
    ... 8 common frames omitted

问题定位

按照错误日志，一步步debug

private void createWebServer() {
   WebServer webServer = this.webServer;
   ServletContext servletContext = getServletContext();
   if (webServer == null && servletContext == null) {
       // 第一次会获取webServerFactory
      ServletWebServerFactory factory = getWebServerFactory();
      this.webServer = factory.getWebServer(getSelfInitializer());
   }
   else if (servletContext != null) {
      try {
         getSelfInitializer().onStartup(servletContext);
      }
      catch (ServletException ex) {
         throw new ApplicationContextException("Cannot initialize servlet context",
               ex);
      }
   }
   initPropertySources();
}

protected ServletWebServerFactory getWebServerFactory() {
   // Use bean names so that we don't consider the hierarchy
   String[] beanNames = getBeanFactory()
         .getBeanNamesForType(ServletWebServerFactory.class);
   if (beanNames.length == 0) {
       // 错误主要是这里抛出的,也就是没有初始化ServletWebServerFactory这个类
      throw new ApplicationContextException(
            "Unable to start ServletWebServerApplicationContext due to missing "
                  + "ServletWebServerFactory bean.");
   }
   if (beanNames.length > 1) {
      throw new ApplicationContextException(
            "Unable to start ServletWebServerApplicationContext due to multiple "
                  + "ServletWebServerFactory beans : "
                  + StringUtils.arrayToCommaDelimitedString(beanNames));
   }
   return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}

具体spring boot怎么初始化tomcat的，请搜索其他资料。我们主要用到的是这个类TomcatServletWebServerFactory

image-20200518185508165.png

看到这边我们就大概可以定位到问题了，就是TomcatServletWebServerFactory这个类没有被初始化。

问题解决

所以思考下我们做了什么操作？我们将tomcat包设置了<scope>provided</scope>，我们本意是打包的时候才不需要将这个包加入lib里面，正常调试编译是可以编译到的，那么可不可能是编译器的问题呢？

我们打开idea运行时的配置Run=>Edit configurations

image-20200518190240842.png

好了，看到这里，问题就知道怎么解决了，原先这个没打勾，也就是运行的时候，不会将<scope>provided</scope>的包加入编译，我们将这个打钩，重新运行一下，问题就解决了。

这个参数跟idea版本有关系，在下面这个版本之后就被默认打钩了。

image-20200518192028370.png