This error occurs because JPA 1 API is brought in, but method getValidationMode exists only since JPA 2.
Instead of following
<dependency>
<groupId>javax.persistence</groupId>
<artifactId>persistence-api</artifactId>
<version>1.0.2</version>
</dependency>
for example one offered by Hibernate can be used:
<dependency>
<groupId>org.hibernate.javax.persistence</groupId>
<artifactId>hibernate-jpa-2.0-api</artifactId>
<version>1.0.1.Final</version>
</dependency>