gistfile1.java

public class Repository<T> 
    public Repository<T> fromEntity(){
        return this;
    }
    
    public Where<T> where(){
        Map<String, Object> parameters = new HashMap<String, Object>;
        return new Where<T>(parameters);
    }
    
    public static class Where<T> {
        private Map<String, Object> parameters;
        
        private String field;
        private Object value;
        
        public Where(Map<String, Object> parameters){
            this.parameters = parameters;
        }
        
        public Where<T> field(String field){
            this.field = field;
        }        
        
        public Where<T> equalTo(Object value){
            this.value = value;
            return this;
        }
        
        public Where<T> and(){
            this.parameters.put(field, value);
            return new Where<T>(this.parameters);
        }
        
        public Then<T> then(){
            return new Then<T>(this.parameters);
        }
    }
    
    public static class Then<T>{
        private Map<String, Object> parameters;

        public Then(Map<String, Object> parameters){
            this.parameters = parameters;
        }

        public List<T> get(){
            return fetchBy(fields);
        }
        
         private List<T> fetchBy(Map<String, Object> fields) {
                Root<T> root = criteriaQuery.from(entity);
                fields.forEach((field, value) -> {
                        criteriaQuery.where(criteriaBuilder.equal(root.get(field), value));
                });
               
                return em.createQuery(criteriaQuery).getResultList();
        }
    }
}