Generic implementation of JPA DAOs and Services with Spring 4.0.0 requiring no additional code written for basic CRUD.

AbstractGenericDAOImpl

package com.pietervaneeckhout.dao.impl;

import com.pietervaneeckhout.dao.GenericDao;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;

/**
 *
 * @author pveeckhout
 */
public abstract class AbstractGenericDAOImpl<T> implements GenericDao<T> {

    private final Class<T> type;

    @PersistenceContext
    private EntityManager entityManager;

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

    @Override
    public List<T> findAll() {
        CriteriaBuilder builder = this.entityManager.getCriteriaBuilder();
        CriteriaQuery<T> cq = builder.createQuery(type);
        Root<T> root = cq.from(type);
        cq.select(root);
        return this.entityManager.createQuery(cq).getResultList();
    }

    @Override
    public T update(T object) {
        return this.entityManager.merge(object);
    }

    @Override
    public T get(Long id) {
        return this.entityManager.find(type, id);
    }

    @Override
    public void delete(T object) {
        this.entityManager.remove(this.entityManager.merge(object));
    }

    @Override
    public void insert(T object) {
        this.entityManager.persist(object);
    }

    @Override
    public boolean exists(Long id) {
        T entity = this.entityManager.find(this.type, id);
        return entity != null;
    }

}

AbstractGenericManagerImpl

package com.pietervaneeckhout.service.impl;

import com.pietervaneeckhout.dao.impl.AbstractGenericDAOImpl;
import com.pietervaneeckhout.service.GenericManager;
import java.util.List;
import javax.transaction.Transactional;
import org.springframework.beans.factory.annotation.Autowired;

/**
 *
 * @author pveeckhout
 */
public abstract class GenericManagerImpl<T, T_DAO extends GenericDAOImpl<T>> implements GenericManager<T> {

    @Autowired
    private T_DAO tDAO;

    @Override
    public List<T> findAll() {
        return tDAO.findAll();
    }

    @Override
    @Transactional
    public T update(T object) {
        return tDAO.update(object);
    }

    @Override
    public T get(Long id) {
        return tDAO.get(id);
    }

    @Override
    @Transactional
    public void delete(T object) {
        tDAO.delete(object);
    }

    @Override
    @Transactional
    public void insert(T object) {
        tDAO.insert(object);
    }

    @Override
    public boolean exists(Long id) {
        return tDAO.exists(id);
    }

}

class linkage

DAO:
AbstractGenericDAOImpl implemets GenericDAO interface
classDAO interface extends GenericDAO interface
classDAOImpl extends AbstractGenericDAOImpl implements classDAO interface

Services:
AbstractGenericManagerImpl implemets GenericManager interface
classManager interface extends GenericManager interface
classManagerImpl extends AbstractGenericmanagerImpl implements classManager interface

DAO creation example

/**
 * 
 * Using the Post class as example
 *
 * @author pveeckhout
 */
public interface postDAO extends GenericDao<Post> {
}

@Repository
public class PostDAOImpl extends AbstractGenericDAOImpl<Post> implements postDAO {

    public PostDAOImpl() {
        super(Post.class);
    }
    
}

Generic Manager

package com.pietervaneeckhout.service;

import java.util.List;

/**
 *
 * @author pveeckhout
 */
public interface GenericManager<T> {

    public List<T> findAll();

    public T update(T object);

    public T get(Long id);

    public void delete(T object);

    public void insert(T object);

    public boolean exists(Long id);
}

GenericDAO

package com.pietervaneeckhout.dao;

import java.util.List;

/**
 *
 * @author pveeckhout
 * @param <T> The class to be persisted
 */
public interface GenericDao<T> {

    public List<T> findAll();

    public T update(T object);

    public T get(Long id);

    public void delete(T object);

    public void insert(T object);

    public boolean exists(Long id);
}

Service creation example

/**
 *
 * Using the Post class as example
 * 
 * @author pveeckhout
 */
public interface PostManager extends GenericManager<Post> {
    
}

@Service
public class PostManagerImpl extends GenericManagerImpl<Post, PostDAOImpl> implements PostManager {
    
}