Hibernate 5 does not respect settings for foreign key naming via xml mapping files in following tags: joined-subclass, set (for many-to-many and one-to-many). For many-to-one setting foreign key name still works. So database created with xml mappings using Hibernate 4 is ok, every foreign key has a right name. When I want to use hibernate 5 to access database data, database is modified by adding new foreign keys with generated names.
For example (using hibernate 5 to create database):
<hibernate-mapping>
<joined-subclass extends="model.Person" lazy="false" name="model.Child" table="CHILDEREN">
<key foreign-key="FK_CHILD_PERSON">
<column name="CHILD_ID"/>
</key>
<many-to-one cascade="save-update" class="model.Address" column="ADRES_ID" foreign-key="FK_CH_AD" name="address" unique="false"/>
</joined-subclass>
</hibernate-mapping>

Results in:
create table CHILDEREN (
CHILD_ID integer not null,
ADRES_ID integer,
EMP_ID integer,
primary key (CHILD_ID)
) ENGINE=InnoDB
alter table CHILDEREN

• add constraint FK98jk84qyyfgwf36x0ferbvkw7 *
  foreign key (CHILD_ID)
  references PERSONS (PER_ID)
  alter table CHILDEREN
  add constraint *FK_CH_AD *
  foreign key (ADRES_ID)
  references ADDRESSES (ADDRESS_ID)

Second example:
<hibernate-mapping>
<joined-subclass extends="model.Person" lazy="false" name="model.Employee" table="EMPLOYEES">
<key foreign-key="FK_EMP_PER">
<column name="EMP_ID"/>
</key>
<many-to-one cascade="save-update" class="model.Address" column="ADDRESS_ID" foreign-key="FK_EMP_AD" name="address" unique="false"/>
<property name="position" type="java.lang.String">
<column name="POSITION"/>
</property>
<many-to-one cascade="save-update" class="model.Department" column="DEP_ID" foreign-key="FK_EMP_DEP" name="department" unique="false"/>
<set cascade="save-update" embed-xml="true" lazy="true" name="children">
<key foreign-key="FK_CHIL_EMP">
<column name="EMP_ID"/>
</key>
<one-to-many class="model.Child"/>
</set>
<set cascade="save-update" lazy="true" name="projects" table="EMP_PROJ">
<key foreign-key="FK_PROJ_EMP">
<column name="EMP_ID"/>
</key>
<many-to-many class="model.Project" column="PROJ_ID"/>
</set>
</joined-subclass>
</hibernate-mapping>

results in:
create table EMPLOYEES (
EMP_ID integer not null,
ADDRESS_ID integer,
POSITION varchar(255),
DEP_ID integer,
primary key (EMP_ID)
) ENGINE=InnoDB
create table EMP_PROJ (
EMP_ID integer not null,
PROJ_ID integer not null,
primary key (EMP_ID, PROJ_ID)
) ENGINE=InnoDB
alter table EMP_PROJ
add constraint *FK3jwurn9su7kn5fssmtfiikx2q *
foreign key (EMP_ID)
references EMPLOYEES (EMP_ID)

alter table EMPLOYEES
add constraint FKptnlm1vgga8r2sq14l04kiyxr
foreign key (EMP_ID)
references PERSONS (PER_ID)

alter table EMPLOYEES
add constraint FK_EMP_AD
foreign key (ADDRESS_ID)
references ADDRESSES (ADDRESS_ID)

alter table EMPLOYEES
add constraint FK_EMP_DEP
foreign key (DEP_ID)
references DEPARTMENTS (DEP_ID)