核心代码之优化查询

public class QueryHelper {
 
 //from子句
 private String fromClause = "";
 //where子句
 private String whereClause = "";
 //order by子句
 private String orderByClause = "";
 
 
 //?
 private List<Object> parameters;
 
    //排序顺序
 public static String ORDER_BY_DESC = "DESC"; //降序
 public static String ORDER_BY_ASC = "ASC"; //升序
 /**
  * 构造from 子句
  * @param clazz 实体类
  * @param alias 实体类对应的别名
  */
 public QueryHelper(Class clazz,String alias){
  fromClause = "FROM " + clazz.getSimpleName() + " " + alias;
 }
 
 /**
  * 构造where子句
  * @param condition 查询条件语句；例如 i.title like ?
  * @param objects 查询语句中？对应查询条件的值；例如：%标题%
  */
 public void addCondition(String condition,Object... params){
  if(condition.length() > 1){  //说明已经有where
   whereClause += " AND " + condition;
  }else{ //无where
   whereClause += " WHERE " + condition;
  }
  
  
  //设置查询条件值到查询条件集合中
  if(parameters == null){
   parameters = new ArrayList<Object>();
  }
  if (params != null) {
   for (Object param : params) {
    parameters.add(param);
   }
  }
 }
 
 /**
  * 构造OrederBy子句
  * @param property 排序属性 如 i.createTime
  * @param order 排序顺序 如
  */
 public void addOrederByProperty(String property,String order) {
  if(orderByClause.length() > 1){  //非第一个排序属性
   orderByClause += "," + property + " " + order;
  }else{ //第一次排序
   orderByClause += " ORDER BY " + property + " " + order;
  }
 }
 
 //查询hql语句
 public String getQueryListHql() {
  return fromClause + whereClause + orderByClause;
 }
 //查询hql语句中?对应的查询条件集合
 public List<Object> getParameters(){
  return parameters;
 }
}