一、場景

Springboot使用@ServerEndpoint來建立websocket鏈接。引入依賴。

<dependency>  
    <groupId>org.springframework.boot</groupId>  
    <artifactId>spring-boot-starter-websocket</artifactId>  
</dependency>

配置Websocket

@Configuration  
@EnableWebSocket  
public class WebSocketConfig {  
  
    @Bean  
    public ServerEndpointExporter serverEndpointExporter() {  
        return new ServerEndpointExporter();  
    }  
}

二、報錯信息

springboot項目添加websocket依賴后運行測試類報如下錯誤：

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2024-01-15 10:27:30.908 ERROR 20552 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'serverEndpointExporter' defined in class path resource [org/springblade/lab/external/webScoket/WebSocketConfig.class]: 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:1804)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:620)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335)
    at org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$211/1936375962.getObject(Unknown Source)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:955)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:929)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:591)
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:732)
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:409)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:308)
    at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:164)
    at org.springblade.core.launch.BladeApplication.run(BladeApplication.java:49)
    at org.springblade.Application.main(Application.java:33)
Caused by: java.lang.IllegalStateException: javax.websocket.server.ServerContainer not available
    at org.springframework.util.Assert.state(Assert.java:76)
    at org.springframework.web.socket.server.standard.ServerEndpointExporter.afterPropertiesSet(ServerEndpointExporter.java:107)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1863)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1800)
    ... 17 common frames omitted

三、排查思路

報的錯誤是創(chuàng)建ServerEndpointExporterBean失敗，原因是ServerContainer不可用，那么我們就去看到ServerContainer在ServerEndpointExporter中是怎么注入的。

點進(jìn)去ServerEndpointExporter()類，
在第49行代碼打上debug跑一下

選中第50行代碼，右鍵，執(zhí)行計算，或者使用快捷鍵Crtl+U

計算結(jié)果發(fā)現(xiàn)是null

四、分析原因

為什么servletContext會返回null，定位到 ServerContainer 類，發(fā)現(xiàn)他是一個接口，那必定注入的時候是有相應(yīng)的實現(xiàn)類，點擊查看實現(xiàn)，居然有五個實現(xiàn)類，那就可以推斷是依賴沖突導(dǎo)致不知道要注入哪個實現(xiàn)，最后獲取Bean的時候返回了null。

點進(jìn)去getAttribute方法，查看實現(xiàn)類

這里有五個實現(xiàn)類，三個是tomcat的，一個是undertow的，還有一個是springframework的，所以解決辦法就是排除掉其他的實現(xiàn)類，只保留springframework這個就行。

五、解決辦法

安裝Maven Helper插件，打開項目的pom.xml文件，點擊pom文件左下角的Dependency Analyzer排除掉多余的依賴。

最終結(jié)果：

      <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <!--添加以下排除方法-->
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-tomcat</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

    <!--websocket服務(wù)-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-websocket</artifactId>
             <!--添加以下排除方法-->
            <exclusions>
                <exclusion>
                    <artifactId>spring-boot-starter-web</artifactId>
                    <groupId>org.springframework.boot</groupId>
                </exclusion>
            </exclusions>
        </dependency>

再次啟動，一切正常！

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