public class DepartmentTestDTO {   
    private Long deptId;
    private String deptName;
    private String deptLocation;

    private Long noOfEmployees;

    private Set<EmployeeTestDTO> empTestDTOlist;
        //setters and getters
}


public class EmployeeTestDTO {


    private Long empId;
    private String empName;
    private String empAddress;
    private String email;
     //setters and getters

}


<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 8 Jul, 2013 7:58:38 PM by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
    <class name="com.OneToMany.EmployeeTestDTO" table="EMPLOYEE_TEST">
        <id name="empId" type="java.lang.Long">
            <column name="EMP_ID" />
            <generator class="increment" />
        </id>
        <property name="empName" type="java.lang.String">
            <column name="EMP_NAME" />
        </property>
        <property name="empAddress" type="java.lang.String">
            <column name="EMP_ADDRESS" />
        </property>
        <property name="email" type="java.lang.String">
            <column name="EMAIL" />
        </property>
    </class>
</hibernate-mapping>


<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 8 Jul, 2013 7:58:38 PM by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
    <class name="com.OneToMany.DepartmentTestDTO" table="DEPARTMENT_TEST">
        <id name="deptId" type="java.lang.Long">
            <column name="DEPT_ID" />
            <generator class="increment" />
        </id>
        <property name="deptName" type="java.lang.String">
            <column name="DEPT_NAME" />
        </property>
        <property name="deptLocation" type="java.lang.String">
            <column name="DEPT_LOCATION" />
        </property>
        <set name="empTestDTOlist" table="EMPLOYEE_TEST" inverse="false" lazy="false"  fetch="select"
          cascade="save-update">
            <key>
                <column name="DEPT_ID" />
            </key>
            <one-to-many class="com.OneToMany.EmployeeTestDTO" />
        </set>
    </class>
</hibernate-mapping>

Criteria criteria = session.createCriteria(DepartmentTestDTO.class);

        criteria.createAlias("empTestDTOlist", "emp");

        ProjectionList projectionList = Projections.projectionList()
                 .add(Projections.property("deptId").as("deptId"))
                 .add(Projections.property("deptName").as("deptName"))
                 .add(Projections.property("empTestDTOlist").as("empTestDTOlist"));     


        criteria.add(Restrictions.eq("deptName", "HR"));
        criteria.setResultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY);

        criteria.setProjection(projectionList);

        criteria.setResultTransformer(Transformers
                .aliasToBean(DepartmentTestDTO.class));

        List list = criteria.list();

Hibernate: select this_.DEPT_ID as y0_, this_.DEPT_NAME as y1_, this_.DEPT_ID as y2_ from DEPARTMENT_TEST this_ inner join EMPLOYEE_TEST emp1_ on this_.DEPT_ID=emp1_.DEPT_ID where this_.DEPT_NAME=?
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 2
    at org.hibernate.loader.criteria.CriteriaLoader.getResultRow(CriteriaLoader.java:166)