@Entity
@Table(name = "myentity")
public class SomeEntity implements Serializable {

    private static final long serialVersionUID = 1L;

    @Column(unique = true, nullable = false, name = "somefield")
    @NotNull
    private String somefield;
}

caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '54533355000175' for key 'UK_bg2tfjjhyqxens7cw8a4uhscw'
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
    at com.mysql.jdbc.Util.getInstance(Util.java:408)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:935)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3973)

Duplicate entry '54533355000175' for key 'UK_bg2tfjjhyqxens7cw8a4uhscw'

@Entity
@Table(name = "myentity", uniqueConstraints = {
  @UniqueConstraint(name = "theNameIWant"), columnNames={"somefield"},
  ... other constraints ...
}
)
public class SomeEntity implements Serializable {

    private static final long serialVersionUID = 1L;

    @Column(unique = true, nullable = false, name = "somefield")
    @NotNull
    private String somefield;
}