1 import java.lang.reflect.Field;
2 import java.sql.Connection;
3 import java.sql.DriverManager;
4 import java.sql.PreparedStatement;
5 import java.sql.ResultSet;
6 import java.sql.ResultSetMetaData;
7 import java.sql.SQLException;
8 import java.util.ArrayList;
9 import java.util.HashMap;
10 import java.util.List;
11 import java.util.Map;
12
13 public class DBUtils {
14
15 // 表示定义数据库的用户名
16 private static String USERNAME = "root";
17 // 定义数据库的密码
18 private static String PASSWORD = "root";
19 // 定义数据库的驱动信息
20 private static String DRIVER = "com.mysql.jdbc.Driver";
21 // 定义访问数据库的地址
22 private static String URL = "jdbc:mysql://localhost:3306/db";
23
24 private static DBUtils per = null;
25 // 定义数据库的链接
26 private Connection con = null;
27 // 定义sql语句的执行对象
28 private PreparedStatement pstmt = null;
29 // 定义查询返回的结果集合
30 private ResultSet resultSet = null;
31
32 private DBUtils() {
33
34 }
35
36 /**
37 * 单例模式，获得工具类的一个对象
38 *
39 * @return
40 */
41 public static DBUtils getInstance() {
42 if (per == null) {
43 per = new DBUtils();
44 per.registeredDriver();
45 }
46 return per;
47 }
48
49 private void registeredDriver() {
50 // TODO Auto-generated method stub
51 try {
52 Class.forName(DRIVER);
53 System.out.println("注册驱动成功！");
54 } catch (ClassNotFoundException e) {
55 // TODO Auto-generated catch block
56 e.printStackTrace();
57 }
58 }
59
60 /**
61 * 获得数据库的连接
62 *
63 * @return
64 */
65 public Connection getConnection() {
66 try {
67 con = DriverManager.getConnection(URL, USERNAME, PASSWORD);
68 } catch (SQLException e) {
69 // TODO Auto-generated catch block
70 e.printStackTrace();
71 }
72 System.out.println("连接数据库成功!!");
73 return con;
74 }
75
76 /**
77 * 完成对数据库的表的添加删除和修改的操作
78 *
79 * @param sql
80 * @param params
81 * @return
82 * @throws SQLException
83 */
84 public boolean executeUpdate(String sql, List<Object> params)
85 throws SQLException {
86
87 boolean flag = false;
88
89 int result = -1; // 表示当用户执行添加删除和修改的时候所影响数据库的行数
90
91 pstmt = con.prepareStatement(sql);
92
93 if (params != null && !params.isEmpty()) {
94 int index = 1;
95 for (int i = 0; i < params.size(); i++) {
96 pstmt.setObject(index++, i);
97 }
98 }
99
100 result = pstmt.executeUpdate();
101 flag = result > 0 ? true : false;
102
103 return flag;
104 }
105
106 /**
107 * 从数据库中查询数据
108 *
109 * @param sql
110 * @param params
111 * @return
112 * @throws SQLException
113 */
114 public List<Map<String, Object>> executeQuery(String sql,
115 List<Object> params) throws SQLException {
116 List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
117 int index = 1;
118 pstmt = con.prepareStatement(sql);
119 if (params != null && !params.isEmpty()) {
120 for (int i = 0; i < params.size(); i++) {
121 pstmt.setObject(index++, params.get(i));
122 }
123 }
124 resultSet = pstmt.executeQuery();
125 ResultSetMetaData metaData = resultSet.getMetaData();
126 int cols_len = metaData.getColumnCount();
127 while (resultSet.next()) {
128 Map<String, Object> map = new HashMap<String, Object>();
129 for (int i = 0; i < cols_len; i++) {
130 String cols_name = metaData.getColumnName(i + 1);
131 Object cols_value = resultSet.getObject(cols_name);
132 if (cols_value == null) {
133 cols_value = "";
134 }
135 map.put(cols_name, cols_value);
136 }
137 list.add(map);
138 }
139 return list;
140
141 }
142
143 /**
144 * jdbc的封装可以用反射机制来封装,把从数据库中获取的数据封装到一个类的对象里
145 *
146 * @param sql
147 * @param params
148 * @param cls
149 * @return
150 * @throws Exception
151 */
152 public <T> List<T> executeQueryByRef(String sql, List<Object> params,
153 Class<T> cls) throws Exception {
154 List<T> list = new ArrayList<T>();
155 int index = 1;
156 pstmt = con.prepareStatement(sql);
157 if (params != null && !params.isEmpty()) {
158 for (int i = 0; i < params.size(); i++) {
159 pstmt.setObject(index++, params.get(i));
160 }
161 }
162 resultSet = pstmt.executeQuery();
163 ResultSetMetaData metaData = resultSet.getMetaData();
164 int cols_len = metaData.getColumnCount();
165 while (resultSet.next()) {
166 T resultObject = cls.newInstance(); // 通过反射机制创建实例
167 for (int i = 0; i < cols_len; i++) {
168 String cols_name = metaData.getColumnName(i + 1);
169 Object cols_value = resultSet.getObject(cols_name);
170 if (cols_value == null) {
171 cols_value = "";
172 }
173 Field field = cls.getDeclaredField(cols_name);
174 field.setAccessible(true); // 打开javabean的访问private权限
175 field.set(resultObject, cols_value);
176 }
177 list.add(resultObject);
178 }
179 return list;
180
181 }
182
183 public void closeDB() {
184 if (resultSet != null) {
185 try {
186 resultSet.close();
187 } catch (SQLException e) {
188 // TODO Auto-generated catch block
189 e.printStackTrace();
190 }
191 }
192 if (pstmt != null) {
193 try {
194 pstmt.close();
195 } catch (SQLException e) {
196 // TODO Auto-generated catch block
197 e.printStackTrace();
198 }
199 }
200 if (con != null) {
201 try {
202 con.close();
203 } catch (SQLException e) {
204 // TODO Auto-generated catch block
205 e.printStackTrace();
206 }
207 }
208 }
209
210
211
212 }
测试：
1 import java.sql.SQLException;
2 import java.util.ArrayList;
3 import java.util.HashSet;
4 import java.util.List;
5 import java.util.Map;
6 import java.util.Set;
7
8
9 public class Test {
10
11 /**
12 * @param args
13 */
14 public static void main(String[] args) {
15 // TODO Auto-generated method stub
16
17 DBUtils db = DBUtils.getInstance();
18 db.getConnection();
19 String sql = "SELECT name,introduction,location FROM activity WHERE id IN(SELECT activityId from mem_act_collect where memberId = ?)";
20 List<Activity> reslist = new ArrayList<Activity>();
21 List<Object> list = new ArrayList<Object>();
22 list.add(2014303342);
23
24 try {
25 reslist = db.executeQueryByRef(sql,list,Activity.class);
26
27 for(Activity ac:reslist){
28 System.out.println(ac.toString());
29 }
30
31
32 } catch (Exception e) {
33 // TODO Auto-generated catch block
34 e.printStackTrace();
35 }finally{
36 db.closeDB();
37 }
38
39 }
40
41 }
时间： 2024-10-18 14:01:28