java - 在 Java 中使用 EntityManager 和 Criteria 时出现 NullPointerException

Question

我创建了一个类，它根据前端应用程序中填充的一些过滤器进行查询。基本上有 3 个过滤器:“标题”、“开始日期”和“结束日期”。以下是我面临的问题:

当我单独发送标题而没有日期时，系统工作正常； 当我发送带有日期的标题时，系统工作正常，正确返回对象列表； 当我发送没有标题的日期时，系统会抛出 NullPointerException。

public class RacRepositoryImpl implements RacRepositoryQuery  {

@PersistenceContext
private EntityManager entityManager;

@Override
public List<Rac> filtrar(RacFilter racFilter) throws Exception {
    CriteriaBuilder builder = entityManager.getCriteriaBuilder();
    CriteriaQuery<Rac> query = builder.createQuery(Rac.class);
    Root<Rac> from = query.from(Rac.class);

    Predicate predicate = builder.and();

    //title
    if (racFilter.getTitulo() != null & racFilter.getTitulo().length() > 2) {
                predicate = builder.and(predicate, 
                builder.like(from.<String>get("titulo"), "%"+racFilter.getTitulo()+"%"));
    }

    //startDate
    if (racFilter.getDataInicial() != null) {
        predicate = builder.and(predicate,
                builder.greaterThanOrEqualTo(from.<Date>get("dataHora"), racFilter.getDataInicial()));
    }

    //finalDate
    if (racFilter.getDataFinal() != null) {
        predicate = builder.and(predicate,
                builder.lessThanOrEqualTo(from.<Date>get("dataHora"), racFilter.getDataFinal()));
    }

    // here it throws the NullPointer exception when I don't send the title information 
    TypedQuery<Rac> typedQuery = entityManager.createQuery(
        query.select(from )
        .where( predicate )
    );

    try {

        List<Rac> results = typedQuery.getResultList();
        return results;

    } catch (Exception e) {
        throw new Exception("not found");
    }


}

我不会发布其他类，因为我已经调试过并且该类的属性很好。问题是当我不发送字段“title”时，这意味着当它为空(不是必需的)时，查询不起作用

Answer 1

NullPointerException 的来源很可能在这里:

//title
if (racFilter.getTitulo() != null & racFilter.getTitulo().length() > 2) {

请将“&”替换为“&&”并查看结果。