java持久化层实现例子，运用jpa EntityManager实体管理器

@PersistenceContext
    private EntityManager em;

@Override
    public DataFile getDataFile(String batchNo, String fileBatchNo) {

        StringQuery query = StringQuery.newQuery()
                .query("from DataFile where ")
                .predicateHasText(batchNo)
                .query(" batchNo=:batchNo")
                .param("batchNo", batchNo)
                .predicateHasText(fileBatchNo)
                .query(" and  fileBatchNo=:fileBatchNo")
                .param("fileBatchNo", fileBatchNo)
                .build();

        List
 
   list = this.find(query);
        if (!CollectionUtils.isEmpty(list)) {
            return list.get(0);
        }
        return null;
    }



    public List
  
    find(StringQuery stringQuery) { //断言 Assert.notNull(stringQuery, "StringQuery must not be null!"); String query = stringQuery.getQuery(); NamedParams params = stringQuery.getParams(); return this.find(query, params); } public List
   
     find(String queryString, NamedParams params) { Assert.notNull(queryString, "Query must not be null!"); Assert.notNull(params, "NamedParams must not be null!"); Query query = this.em.createQuery(queryString); this.setQueryParams(query, params); return query.getResultList(); }