Base JPA Repository that supports easier dynamic query building.

FlexibleJpaRepository.java

package it.murah.license.server.jpa;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import javax.persistence.EntityManager;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Path;
import javax.persistence.criteria.Root;

import org.springframework.data.jpa.repository.support.JpaEntityInformation;
import org.springframework.data.jpa.repository.support.SimpleJpaRepository;

/**
 * Makes it easy handling variable property name/values, including inner object
 * properties.
 * <p>
 * e.g.:<br>
 * map.put("prop1", 1); <br>
 * map.put("child.prop", "foo");
 * <p>
 * findAllBy(map); // select * from T where prop1=1 and child.prop='foo'
 * 
 * @since 2019-04-16
 * @author Ulisses Lima
 */
public class FlexibleJpaRepository<T, ID extends Serializable> extends SimpleJpaRepository<T, ID> {
	private final EntityManager em;
	private final JpaEntityInformation<T, ID> ei;

	public FlexibleJpaRepository(JpaEntityInformation<T, ID> ei, EntityManager em) {
		super(ei, em);
		this.em = em;
		this.ei = ei;
	}

	public List<T> findAllBy(Map<String, Object> params) {
		Class<T> type = ei.getJavaType();
		CriteriaBuilder cb = em.getCriteriaBuilder();

		CriteriaQuery<T> q = cb.createQuery(type);
		Root<T> props = q.from(type);

		List<javax.persistence.criteria.Predicate> predicates = new ArrayList<>();
		params.forEach((key, val) -> {
			String[] path = key.split("\\.");
			Path<Object> x = props.get(path[0]);
			if (path.length > 1) {
				for (int i = 1; i < path.length; i++) {
					x = x.get(path[i]);
				}
			}
			predicates.add(cb.equal(x, val));
		});

		q.where(cb.and(predicates.toArray(new javax.persistence.criteria.Predicate[predicates.size()])));
		q.orderBy(cb.asc(props.get("id")));

		return em.createQuery(q.select(props)).setMaxResults(1000).getResultList();
	}
}