(Springboot)java.lang.IllegalStateException: A SockJsMessageCodec is required but not available:

這個問題是版本不兼容造成的，pom.xml如下：

    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>im</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.10.RELEASE</version>
        <relativePath /> <!-- lookup parent from rsepository -->
    </parent>
    <properties>
        <java.version>1.8</java.version>
        <thymeleaf.version>3.0.0.RELEASE</thymeleaf.version>
        <thymeleaf-layout-dialect.version>2.0.0</thymeleaf-layout-dialect.version>
    </properties>

    <dependencies>

        <!-- Compile -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-websocket</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-tomcat</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

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

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

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

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>ch.qos.logback</groupId>
                    <artifactId>logback-classic</artifactId>
                </exclusion>
            </exclusions>
            <version>1.2.30</version>
        </dependency>

        <!-- 靜態資源 -->
        <dependency>
            <groupId>org.webjars</groupId>
            <artifactId>webjars-locator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.webjars</groupId>
            <artifactId>sockjs-client</artifactId>
            <version>1.0.2</version>
        </dependency>
        <dependency>
            <groupId>org.webjars</groupId>
            <artifactId>stomp-websocket</artifactId>
            <version>2.3.3</version>
        </dependency>
        <dependency>
            <groupId>org.webjars</groupId>
            <artifactId>bootstrap</artifactId>
            <version>3.3.7</version>
        </dependency>
        <dependency>
            <groupId>org.webjars</groupId>
            <artifactId>jquery</artifactId>
            <version>3.1.0</version>
        </dependency>
         **<dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>          
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>           
        </dependency>**
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <fork>true</fork>
                </configuration>
            </plugin>
        </plugins>
    </build>

問題就是出在在：

    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>          
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>           
    </dependency>

默認的版本是2.8.4，應該把版本降低一些，比如：

   <dependency>
     <groupId>com.fasterxml.jackson.core</groupId>
       <artifactId>jackson-core</artifactId>
       <version>2.7.3</version>
   </dependency>
  <dependency>
       <groupId>com.fasterxml.jackson.core</groupId>
       <artifactId>jackson-databind</artifactId>
       <version>2.7.3</version>
   </dependency>

問題解決