Generic DAO, Spring, Hibernate

Question

I want to understand how can i implement the generic methods like add, edit, delete and search on my database, i have already made the connection (hibernate) and works fine

I do have this method, that works

Class: GenericDAO

public <T> T save(final T o){
        Session session=HibernateUtil.getSessionFactory().openSession();
        Transaction trans=session.beginTransaction();
        Object object = (T) session.save(o);
        trans.commit();
        return (T) object;
    }

and in Main

GenericDAO gen = new GenericDAO();
gen.save(object); 

also i have others methods that i dont know how to use them

Class: GenericDAO

public void delete(final Object object){
   Session session=HibernateUtil.getSessionFactory().openSession();
   Transaction trans=session.beginTransaction();
   session.delete(object);
   trans.commit();
}

/***/
public <T> T get(final Class<T> type, final int id){
    Session session=HibernateUtil.getSessionFactory().openSession();
    Transaction trans=session.beginTransaction();
    Object object = (T) session.get(type, id);
    trans.commit();
    return (T) object;
}

public <T> List<T> getAll(final Class<T> type) {
    Session session=HibernateUtil.getSessionFactory().openSession();
    Transaction trans=session.beginTransaction();
    final Criteria crit = session.createCriteria(type);
    List<T> list = crit.list();
    trans.commit();
    return list;
}

Thank you

Answer 1

I think GenericDAO class is base class. It's not for using directly. Did you check this article ? I checked this article and created a sample project.

• Don't repeat the DAO!

Example

GitHub - generic-dao-hibernate sample

For example, you might want to create an API to retrieve all employees list according to MySQL first step example.

Employees table schema is like following:

Base SQL

    CREATE TABLE employees (
        emp_no      INT             NOT NULL,  -- UNSIGNED AUTO_INCREMENT??
        birth_date  DATE            NOT NULL,
        first_name  VARCHAR(14)     NOT NULL,
        last_name   VARCHAR(16)     NOT NULL,
        gender      ENUM ('M','F')  NOT NULL,  -- Enumeration of either 'M' or 'F'  
        hire_date   DATE            NOT NULL,
        PRIMARY KEY (emp_no)                   -- Index built automatically on primary-key column
                                               -- INDEX (first_name)
                                               -- INDEX (last_name)
    );

O/R Mapping

Hibernate require you to configure mapping object-relation settings. After that, you will enjoy converting object-to-sql and sql-to-object.

Entity class based on SQL

• @Entity, @Table, @Id, @Column, @GeneratedValue are from Hibernate
• @Data, @NoArgsConstructor are from lombok, it reduces getter/setter code

• @XmlRootElement, @XmlAccessorType are from jaxb, you might don't need to use it

  @Entity
  @Data
  @NoArgsConstructor
  @Table(name = "employees")
  @XmlAccessorType(XmlAccessType.FIELD)
  @XmlRootElement
  public class Employees implements Serializable {
  
      private static final long serialVersionUID = 1L;
  
      @Id
      @Column(name = "emp_no", unique = true)
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      private Integer empNo;
  
      @Column(name = "birth_date")
      private Date birthDate;
  
      @Column(name = "first_name")
      private String firstName;
  
      @Column(name = "last_name")
      private String lastName;
  
      @Column(name = "gender")
      @Enumerated(EnumType.STRING)
      private Gender gender;
  
      @Column(name = "hire_date")
      private Date hireDate;
  }
  

Resource Class for Frontend

You always need to write DAO(Data Access Object) for accessing the database. GenericDAO is a method to reduce boilerplate sources codes.

EmployeesResource class

• CRUD operations on WEB API
  • #create, #read, #update or #delete

should be equivalent with

• SQL
  • INSERT, SELECT, UPDATE and DELETE

You need to identify a record or records with key. In this case, id is sample primary key.

    @Path("/employee")
    public class EmployeesResource {

        static Logger log = LoggerFactory.getLogger(EmployeesResource.class);

        @GET
        @Produces(MediaType.APPLICATION_JSON)
        public List<Employees> index(@BeanParam Employees paramBean) {
            EmployeesDao dao = (EmployeesDao) SpringApplicationContext.getBean("employeesDao");
            List<Employees> result = dao.read();
            System.out.println("Get all employees: size = " + result.size());
            return result;
        }

        @GET
        @Path("{id}")
        @Produces(MediaType.APPLICATION_JSON)
        public Employees show(@PathParam("id") Integer id) {
            EmployeesDao dao = (EmployeesDao) SpringApplicationContext.getBean("employeesDao");
            System.out.println("Get employees -> id = " + id);
            return dao.read(id);
        }

        @POST
        @Consumes(MediaType.APPLICATION_JSON)
        public Integer create(Employees obj) {
            EmployeesDao dao = (EmployeesDao) SpringApplicationContext.getBean("employeesDao");
            return dao.create(obj);
        }

        @PUT
        @Path("{id}")
        @Consumes(MediaType.APPLICATION_JSON)
        public void update(Employees obj, @PathParam("id") String id) {
            EmployeesDao dao = (EmployeesDao) SpringApplicationContext.getBean("employeesDao");
            dao.update(obj);
        }

        @DELETE
        @Path("{id}")
        public void destroy(@PathParam("id") Integer id) throws Exception {
            EmployeesDao dao = (EmployeesDao) SpringApplicationContext.getBean("EmployeesDao");
            dao.delete(id);
        }
    }

GenericDao interface & implementation

Interface ( as is from ibm's post )

According to the post, we can declare dao interface. Then we should implement that interface's methods.

    public interface GenericDao<T, PK extends Serializable> {

        /** Persist the newInstance object into database */
        PK create(T newInstance);

        /**
         * Retrieve an object that was previously persisted to the database using
         * the indicated id as primary key
         */
        T read(PK id);
        List<T> read();

        /** Save changes made to a persistent object. */
        void update(T transientObject);

        /** Remove an object from persistent storage in the database */
        void delete(PK id) throws Exception;
        void delete(T persistentObject) throws Exception;
    }

Implementation

    public class GenericDaoHibernateImpl<T, PK extends Serializable> implements GenericDao<T, PK> {

        private Class<T> type;

        @Autowired
        private SessionFactory sessionFactory;

        public SessionFactory getSessionFactory() {
            return sessionFactory;
        }

        public void setSessionFactory(SessionFactory sessionFactory) {
            this.sessionFactory = sessionFactory;
        }

        public GenericDaoHibernateImpl(Class<T> type) {
            this.type = type;
        }

        // Not showing implementations of getSession() and setSessionFactory()
        private Session getSession() {
            Session session = sessionFactory.getCurrentSession();
            return session;
        }

        @Transactional(readOnly = false, rollbackFor = RuntimeException.class)
        public PK create(T o) {
            return (PK) getSession().save(o);
        }

        @Transactional(readOnly = false, rollbackFor = RuntimeException.class)
        public void update(T o) {
            getSession().update(o);
        }

        @Transactional(readOnly = true)
        public T read(PK id) {
            return (T) getSession().get(type, id);
        }

        @SuppressWarnings("unchecked")
        @Transactional(readOnly = true)
        public List<T> read() {
            return (List<T>) getSession().createCriteria(type).list();
        }

        @Transactional(readOnly = false, rollbackFor = RuntimeException.class)
        public void delete(PK id) {
            T o = getSession().load(type, id);
            getSession().delete(o);
        }

        @Transactional(readOnly = false, rollbackFor = RuntimeException.class)
        public void delete(T o) {
            getSession().delete(o);
        }

If you use only simple CRUD operations in the project, you don't need to append any code for SQL operations. For example, you can create another simple SQL tables like divisions_table or personnel_table with using extends GenericDao<Division, Integer> or extends GenericDao<Personnel, Integer>.

EDIT

To instantiate real dao class related with each table, you need to configure applicationContext.xml and beans.

example

<bean id="employeesDao" parent="abstractDao">
    <!-- You need to configure the interface for Dao -->
    <property name="proxyInterfaces">
        <value>jp.gr.java_conf.hangedman.dao.EmployeesDao</value>
    </property>
    <property name="target">
        <bean parent="abstractDaoTarget">
            <constructor-arg>
                <value>jp.gr.java_conf.hangedman.models.Employees</value>
            </constructor-arg>
        </bean>
    </property>
</bean>

P.S.

You need to remember this article was written a decade ago. And, you should think seriously about which O/R mapper is really good or not. I think O/R mapper is slightly declining now. Instead of Hibernate, you can find MyBatis , JOOQ

Answer 2

This is one way to implement a hibernate centric generic DAO. It provides basic CRUD operations along with simple search but can be extended to include other generic features.

IGenericDAO interface

public interface IGenericDAO<T extends Serializable> {

T findOne(long id);

List<T> findAll();

void create(T entity);

void update(T entity);

void delete(T entity);

void deleteById(long entityId);

public void setClazz(Class<T> clazzToSet);

}

AbstractTemplateDAO

import java.io.Serializable;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;

public abstract class AbstractHibernateDAO<T extends Serializable> implements IGenericDAO<T> {

private Class<T> clazz;

@Autowired
SessionFactory sessionFactory;

public final void setClazz(Class<T> clazzToSet) {
    this.clazz = clazzToSet;
}


@Override
public T findOne(long id) {
    return (T) getCurrentSession().get(clazz, id);
}


@Override
public List<T> findAll() {
    return getCurrentSession().createQuery("from " + clazz.getName(),clazz).getResultList();
}


@Override
public void create(T entity) {
    getCurrentSession().persist(entity);
}


@Override
public void update(T entity) {
    getCurrentSession().merge(entity);
}


@Override
public void delete(T entity) {
    getCurrentSession().delete(entity);
}


@Override
public void deleteById(long entityId) {
    T entity = findOne(entityId);
    delete(entity);
}

protected final Session getCurrentSession() {
    return sessionFactory.getCurrentSession();
    }
}

GenericHiberateDAO

Note: the use of scope prototype here. The spring container creates a new instance of the dao on each request.

@Repository
@Scope(BeanDefinition.SCOPE_PROTOTYPE)
public class GenericHibernateDAO<T extends Serializable> extends AbstractHibernateDAO<T> 
implements IGenericDAO<T> {
   //
}

Service class

Shows how to use autowire the generic dao in a service class and pass the model class a parameter. Also, do note that this implementation uses @Transactional annotation for spring transaction management.

@Service
public class TestService implements ITestService {

private IGenericDAO<TestModel> dao;

@Autowired
public void setDao(IGenericDAO<TestModel> daoToSet) {
    dao = daoToSet;
    dao.setClazz(TestModel.class);

}

@Override
@Transactional
public List<TestModel> findAll() {
    return dao.findAll();
}
}

App Config

Shows how to set up spring for automatic transaction management using @EnableTransactionManagement

@Configuration
@ComponentScan("com.base-package")
@EnableTransactionManagement
public class AppConfig {

       // add hibernate configuration

      // add beans


}