We use codehaus jaxb2 plugin and it has encoding-option::
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>jaxb2-maven-plugin</artifactId>
<version>1.5</version>
<executions>
<execution>
<id>xjc_qshgv</id>
<phase>generate-sources</phase>
<goals>
<goal>xjc</goal>
</goals>
<configuration>
...
<encoding>${file.encoding}</encoding>
...
</configuration>
</execution>
</executions>
</plugin>