/**
*
*/
package com.model;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;

/**
* @author singhk
*
*/
@Entity
@Table(name = "EMPLOYEE")
@NamedQueries( { @NamedQuery(name = "findEmpByDept", query = "SELECT i FROM Employee i WHERE i.department=:department"), })
@SequenceGenerator(initialValue = 1, name = "employeeIdSeq", sequenceName = "EMPLOYEE_ID_SEQ")
public class Employee implements Serializable {
   private static final long serialVersionUID = 1L;

   @Id
   @GeneratedValue(generator = "employeeIdSeq", strategy = GenerationType.SEQUENCE)
   private Long id;
   @Column(name = "name", nullable = false)
   private String name;
   @Column(name = "department", nullable = false)
   private String department;

   public Employee() {
      super();
   }

   public Employee(String name, String department) {
      super();
      this.name = name;
      this.department = department;
   }

   public Long getId() {
      return id;
   }

   public String getName() {
      return name;
   }

   public void setName(String name) {
      this.name = name;
   }

   public String getDepartment() {
      return department;
   }

   public void setDepartment(String department) {
      this.department = department;
   }

}

/**
*
*/
package com.model.daoImpl;

import java.util.List;

import com.model.Employee;
import com.model.dao.EmployeeDAO;

/**
* @author singhk
*
*/
public class EmployeeDAOImpl extends GenericDAOImpl<Employee, Long> implements
      EmployeeDAO {

   @SuppressWarnings("unchecked")
   public List<Employee> findEmpByDept(String department) {
      return getEntityManager().createNamedQuery("findEmpByDept")
            .setParameter("department", department).getResultList();
   }
}

package com.model.daoImpl;

import java.io.Serializable;
import java.lang.reflect.ParameterizedType;
import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import com.model.dao.GenericDAO;

public abstract class GenericDAOImpl<T, ID extends Serializable> implements GenericDAO<T,ID>
{
   private Class<T> entityBeanType;
   private EntityManager em;

   @SuppressWarnings("unchecked")
   public GenericDAOImpl()
   {
     this.entityBeanType = (Class<T>) ( (ParameterizedType) getClass().getGenericSuperclass() ).getActualTypeArguments()[0];
   }

   @PersistenceContext
   public void setEntityManager(EntityManager em)
   {
      this.em = em;
   }
   
   public EntityManager getEntityManager()
   {
      return em;
   }

   public T findById(ID id)
   {
      T entity;
   
      
         entity = getEntityManager().find( getEntityBeanType(), id );
      
      
      return entity;
   }

   @SuppressWarnings("unchecked")
   public List<T> findAll()
   {
      List<T> allEntities = getEntityManager().createQuery( "from " + getEntityBeanType().getName() ).getResultList();
      return allEntities;
   }
   
   public void clear()
   {
      getEntityManager().clear();
   }
   
   
   protected Class<T> getEntityBeanType()
   {
      return entityBeanType;
   }
}