import javax.persistence.criteria.CriteriaBuilder;import javax.persistence.criteria.CriteriaQuery;import javax.persistence.criteria.Join;import javax.persistence.criteria.Predicate;import javax.persistence.criteria.Root;import net.sf.json.JSONObject;import net.sf.json.JsonConfig; @Action("courierAction_pageQuery") public String pageQuery() throws Exception {  Pageable pageable = new PageRequest(page-1, rows);  final String courierNum = model.getCourierNum();  final String company = model.getCompany();  final String type = model.getType();  final Standard standard = model.getStandard();    //相當于DetchedCriteria對象.通過specification封裝過濾條件  Specification<Courier> specification = new Specification<Courier>() {      @Override   public Predicate toPredicate(Root<Courier> root, CriteriaQuery<?> query, CriteriaBuilder cb) {    //root：根實體 query：排序，封裝條件 CriteriaBuilder：Predicate斷言工廠，產生Predicate對象    //添加過濾條件:添加快遞員編號條件    //p1:實體中屬性 p2:條件    List<Predicate> list = new ArrayList<>();    if(StringUtils.isNotBlank(courierNum)){     Predicate p1 = cb.equal(root.get("courierNum").as(String.class), courierNum);     list.add(p1);    }    if(StringUtils.isNotBlank(company)){     Predicate p2 = cb.equal(root.get("company").as(String.class), company);     list.add(p2);    }    if(StringUtils.isNotBlank(type)){     Predicate p3 = cb.equal(root.get("type").as(String.class), type);     list.add(p3);    }    //sql : select * from T_COURIER t inner join t_Standard s on t.c_standard_id = s.c_id//    where s.c_name = '標準一（100公斤）';    //JPQL: from Courier c inner join c.standard s where s.name = "";    if(standard!=null && StringUtils.isNotBlank(standard.getName())){     //返回關聯對象     Join<Object, Object> join = root.join("standard");     Predicate p4 = cb.equal(join.get("name").as(String.class), standard.getName());     list.add(p4);    }    if(list.size()==0){     return null;    }    //list集合轉為數組    Predicate[] restrictions = new Predicate[list.size()];    restrictions = list.toArray(restrictions);    return cb.and(restrictions);   }  };  Page<Courier> page = courierService.findAll(specification, pageable);    Map<String, Object> map = new HashMap<>();  map.put("total", page.getTotalElements());  map.put("rows", page.getContent());    //將fixedares集合屬性排除掉，不轉json  JsonConfig jsonConfig = new JsonConfig();  jsonConfig.setExcludes(new String[]{"fixedAreas"});    String json = JSONObject.fromObject(map, jsonConfig).toString();    ServletActionContext.getResponse().setContentType("text/json;charset=utf-8");  ServletActionContext.getResponse().getWriter().write(json);  return NONE; }Dao:public interface CourierDao extends JpaRepository<Courier, Integer>, JpaSpecificationExecutor<Courier> {}