出现错误：

index.js:15 WebSocket connection to 'ws://127.0.0.1:8080/ws' failed: Error during WebSocket handshake: Unexpected response code: 404

pom.xml导入jar包

<!--spring boot的支持 -->
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.1.0.RELEASE</version>
	</parent>

	<groupId>cn.itcast.websocket</groupId>
	<artifactId>itcast-websocket</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>war</packaging>

	<name>itcast-websocket</name>
	<url>http://maven.apache.org</url>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
	</properties>

	<dependencies>
		<!-- <dependency> <groupId>javax</groupId> <artifactId>javaee-api</artifactId> 
			<version>7.0</version> <scope>provided</scope> </dependency> -->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-websocket</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-websocket</artifactId>
			<version>4.1.7.RELEASE</version>
		</dependency>
		<dependency>
			<groupId>javax.websocket</groupId>
			<artifactId>javax.websocket-api</artifactId>
			<version>1.0</version>
			<scope>provided</scope>
		</dependency>

		<dependency>
			<groupId>com.fasterxml</groupId>
			<artifactId>classmate</artifactId>
			<version>1.0.0</version>
		</dependency>

		<dependency>
			<groupId>com.fasterxml.jackson.core</groupId>
			<artifactId>jackson-databind</artifactId>
			<version>2.9.9</version>
		</dependency>
		<dependency>
			<groupId>com.fasterxml.jackson.core</groupId>
			<artifactId>jackson-core</artifactId>
			<version>2.9.9</version>
		</dependency>
		<dependency>
			<groupId>com.fasterxml.jackson.core</groupId>
			<artifactId>jackson-annotations</artifactId>
			<version>2.9.9</version>
		</dependency>
	</dependencies>
	<build>
		<plugins>
			<!-- java编译插件 -->
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.2</version>
				<configuration>
					<source>1.8</source>
					<target>1.8</target>
					<encoding>UTF-8</encoding>
					<failOnMissingWebXml>false</failOnMissingWebXml>
				</configuration>
			</plugin>
			<!-- 配置Tomcat插件 -->
			<plugin>
				<groupId>org.apache.tomcat.maven</groupId>
				<artifactId>tomcat7-maven-plugin</artifactId>
				<version>2.2</version>
				<configuration>
					<port>8082</port>
					<path>/</path>
				</configuration>
			</plugin>
		</plugins>
	</build>

后来，发现漏左注解，添加下面注解就解决了
@Configuration
@EnableWebSocket

package cn.itcast.websocket.spring;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.config.annotation.EnableWebSocket;
import org.springframework.web.socket.config.annotation.WebSocketConfigurer;
import org.springframework.web.socket.config.annotation.WebSocketHandlerRegistry;

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {

	@Override
	public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
		registry.addHandler(myHandler(), "/ws").setAllowedOrigins("*");

	}

	@Bean
	public WebSocketHandler myHandler() {
		return new MyHandler();
	}
}