Note sure about sprint boot, but to get JAXWS working in Java 11, I used
<profiles>
<!-- add back the jaxws SOAP dependendies which were removed in JDK11 -->
<profile>
<id>jdk11</id>
<activation>
<jdk>[11,)</jdk>
</activation>
<!-- tested working with OpenJDK 11.0.8 -->
<dependencies>
<dependency>
<groupId>com.sun.xml.ws</groupId>
<artifactId>jaxws-rt</artifactId>
<version>2.3.3</version>
<type>pom</type>
</dependency>
<dependency>
<groupId>com.sun.xml.ws</groupId>
<artifactId>rt</artifactId>
<version>2.3.3</version>
</dependency>
</dependencies>
</profile>
</profiles>