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();
  
  //相当于DetchedCriteria对象.通过specification封装过滤条件
  Specification<Courier> specification = new Specification<Courier>() {
   
   @Override
   public Predicate toPredicate(Root<Courier> root, CriteriaQuery<"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 = '标准一（100公斤）';
    //JPQL: from Courier c inner join c.standard s where s.name = "";
    if(standard!=null && StringUtils.isNotBlank(standard.getName())){
     //返回关联对象
     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集合转为数组
    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());
  
  //将fixedares集合属性排除掉，不转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> {

}