（十五）条件查询

条件查询信息列表

1、在baseDao、baseDaoImpl中编写和实现findObjects(String hql, List<Object> parameters)

2、在service、serviceImpl中调用baseDao中的条件查询方法

3、在action中用service中新写的findObjects(String hql, List<Object> parameters)进行条件查询

4、添加listUI.jsp中的查询方法。

优化查询-查询工具类QueryHelper

设计一个查询工具类QueryHelper，里面需要对将要查询的hql和参数进行组装，然后将此对象传递给service运用并返回结果。该工具类主要方法有：

① QueryHelper(Class clazz, String alias) 构造器，主要组装from 子句

② addCondition(String condition, Object... param) 组装where子句

③ addOrderByProperty(String property, String order) 组装order by 子句

④ getListQueryHql() 返回查询列表的hql

⑤ getCountQueryHql() 返回统计总记录数的hql

⑥ getParameters() 返回参数列表

具体类实现：

 1 package cn.itcast.core.utils;
 2 
 3 import java.util.ArrayList;
 4 import java.util.List;
 5 
 6 public class QueryHelper {
 7     
 8     //from 子句
 9     private String fromClause = "";
10     //where 子句
11     private String whereClause = "";
12     //order by 子句
13     private String orderByClause = "";
14     
15     //where 子句中?对应的参数值
16     private List<Object> parameters;
17     
18     public static String ORDER_BY_ASC = "ASC";//升序
19     public static String ORDER_BY_DESC = "DESC";//降序
20     
21     /**
22      * 利用构造方法构造from子句
23      * @param clazz 实体类
24      * @param alias 别名
25      */
26     public QueryHelper(Class clazz, String alias){
27         fromClause = "FROM " + clazz.getSimpleName() + " " + alias;
28     }
29     /**
30      * 组装where子句
31      * @param condition 条件
32      * @param params 条件中?对应的参数值
33      * @return QueryHelper
34      */
35     public QueryHelper addCondition(String condition, Object...params){
36         if(whereClause.length() > 0){
37             whereClause += " AND " + condition;
38         } else {
39             whereClause = " WHERE " + condition;
40         }
41         if(parameters == null){
42             parameters = new ArrayList<Object>();
43         }
44         for(Object param: params){
45             parameters.add(param);
46         }
47         return this;
48     }
49     /**
50      * 构建order by 子句
51      * @param property 排序的属性
52      * @param order 升序(asc)或是降序(desc)
53      * @return QueryHelper
54      */
55     public QueryHelper addOrderByProperty(String property, String order){
56         if(orderByClause.length() > 0){
57             orderByClause += "," + property + " " + order;
58         } else {
59             orderByClause += " ORDER BY " + property + " " + order;
60         }
61         return this;
62     }
63 
64     //返回列表查询hql语句
65     public String getListQueryHql(){
66         return fromClause + whereClause + orderByClause;
67     }
68     
69     //返回查询总记录数的hql
70     public String getCountHql(){
71         return "SELECT Count(*) " + fromClause + whereClause;
72     }
73     
74     public List<Object> getParameters() {
75         return parameters;
76     }
77 }