如何用JPA EntityManager实现Java持久化层，改写为长尾？

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Java持久化层实现的例子，使用JPA的EntityManager和@PersistenceContext注解，代码如下：

java@PersistenceContextprivate EntityManager em;

@Overridepublic DataFile getDataFile(String batchNo, String fileBatchNo) { StringQuery query=StringQuery.newQuery();}

java持久化层实现的例子， 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(); }