An example of QueryManager in Java for JPA

QueryManager.java

import javax.persistence.EntityManager;
import javax.persistence.Query;
import java.util.HashMap;
import java.util.Map;

public class QueryBuilder {
    private final EntityManager entityManager;
    private final Map<String, Object> parameters = new HashMap<>();
    private String resultSetMapping;
    private String query;


    public QueryBuilder(EntityManager entityManager) {

        this.entityManager = entityManager;
    }

    public QueryBuilder withQuery(String query) {
        this.query = query;
        return this;
    }

    public QueryBuilder withParameter(String key, Object value) {
        parameters.put(key, value);
        return this;
    }

    public QueryBuilder withResultSetMapping(String resultSetMapping) {
        this.resultSetMapping = resultSetMapping;
        return this;
    }

    public Query build() {
        Query nativeQuery = entityManager.createNativeQuery(query, resultSetMapping);
        for (String name : parameters.keySet()) {
            nativeQuery.setParameter(name, parameters.get(name));
        }

        return nativeQuery;
    }
}