JPA Criteria API with multiple parameters

Concept is to construct array of javax.persistence.Predicate which contains only predicates we want to use:

Example entity to be queried:

@Entity
public class A {
    @Id private Long id;    
    String someAttribute;
    String someOtherAttribute;
    ...
}

Query itself:

    //some parameters to your method
    String param1 = "1";
    String paramNull = null;

    CriteriaBuilder qb = em.getCriteriaBuilder();
    CriteriaQuery cq = qb.createQuery();
    Root<A> customer = cq.from(A.class);

    //Constructing list of parameters
    List<Predicate> predicates = new ArrayList<Predicate>();

    //Adding predicates in case of parameter not being null
    if (param1 != null) {
        predicates.add(
                qb.equal(customer.get("someAttribute"), param1));
    }
    if (paramNull != null) {
        predicates.add(
                qb.equal(customer.get("someOtherAttribute"), paramNull));
    }
    //query itself
    cq.select(customer)
            .where(predicates.toArray(new Predicate[]{}));
    //execute query and do something with result
    em.createQuery(cq).getResultList();

Take a look at this site JPA Criteria API. There are plenty of examples.

Update: Providing a concrete example

Let's search for Accounts with a balance lower than a specific value:

SELECT a FROM Account a WHERE a.balance < :value

First create a Criteria Builder

CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Account> accountQuery = builder.createQuery(Account.class);
Root<Account> accountRoot = accountQuery.from(Account.class);
ParameterExpression<Double> value = builder.parameter(Double.class);
accountQuery.select(accountRoot).where(builder.lt(accountRoot.get("balance"), value));

To get the result set the parameter(s) and run the query:

TypedQuery<Account> query = entityManager.createQuery(accountQuery);
query.setParameter(value, 1234.5);
List<Account> results = query.getResultList();

BTW: The entityManager is injected somewhere in an EJB/Service/DAO.

A simple solution for Spring, using lambda expressions:

Specification<User> specification = (root, query, builder) -> {
    List<Predicate> predicates = new ArrayList<>();

    // like
    predicates.add(builder.like(root.get("name"), "%test%"));

    // equal
    predicates.add(builder.equal(root.get("parent_id"), 99L);


    // AND all predicates
    return builder.and(predicates.toArray(new Predicate[0]));
};

repository.findAll(specification);