解决Spring Boot与WebSocket遇到javax.websocket.server.ServerContainer不可用的问题

原标题：SpringBoot在使用WebSocket时遇到Invocation of init method failed; nested exception is java.lang.IllegalStateException: javax.websocket.server.ServerContainer not available的解决办法

这是异常堆栈：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'serverEndpointExporter' defined in class path resource [xxxxx]: Invocation of init method failed; nested exception is java.lang.IllegalStateException: javax.websocket.server.ServerContainer not available
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1796) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:595) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:879) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:878) ~[spring-context-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) [spring-boot-2.2.2.RELEASE.jar:2.2.2.RELEASE]
	at com.wuqihuyu.sockettest.websockettest.WebSocketTestApplication.main(WebSocketTestApplication.java:10) [classes/:na]
Caused by: java.lang.IllegalStateException: javax.websocket.server.ServerContainer not available
	at org.springframework.util.Assert.state(Assert.java:73) ~[spring-core-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.web.socket.server.standard.ServerEndpointExporter.afterPropertiesSet(ServerEndpointExporter.java:107) ~[spring-websocket-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1855) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1792) ~[spring-beans-5.2.2.RELEASE.jar:5.2.2.RELEASE]
	... 16 common frames omitted


进程已结束,退出代码1

可见大部分堆栈都是在源码里面报的错，此时我们就需要进源码里面看看了，直接进最后一个堆栈的所在位置

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1796)

我们下断点调试可以发现这个方法是一个公共方法，很多类的初始化都会在这里调用

于是我们就需要使用条件断点，断点名称，即beanname必须包含：serverEndpointExporter这个才断点

一步步往里面走

发现它会调用afterPropertiesSet方法

在这里我们可以看到假设getServerContainer为null则会抛出异常，我们看下这个getServerContainer到底返回什么东西

它会把本类的serverContainer直接返回，此时我就有疑问了，这个serverContainer为什么为空呢，我们就需要查找它到底在哪设置值了

这个serverContainer是一个私有变量，即可知道它肯定只能在本类里面通过set赋值，我们直接关键字搜索：

有两个地方，但是我们不知道到底执行哪一个，我们直接两个都下断点，然后重新启动

断点停在了initServletContext方法，在这我们可以看到因为ServletContext为空，所以就给它设置了空值，但ServletContext为什么会为空呢，我们点进去看一下

发现它是一个接口，既然ServletContext是一个接口它肯定有很多实现类，我们看一下都有哪些

除了springboot和tomcat的，还有一个io.undertow.servlet.spec的实现类，这就找到了问题了，估计就是依赖冲突造成springboot在加载的时候加载了错误的ServletContext实现类导致的，搜索了一下果然有一个


        <dependency>
            <groupId>io.undertow</groupId>
            <artifactId>undertow-websockets-jsr</artifactId>
            <version>1.4.17.Final</version>
        </dependency>

直接删掉这个依赖重新运行，发现一切正常。