一个简单的装饰器模式例子，用来体现直接查询，缓存查询，和过滤敏感词汇
1 import java.sql.Connection;
2 import java.sql.PreparedStatement;
3 import java.sql.ResultSet;
4 import java.sql.SQLException;
5 import java.util.ArrayList;
6 import java.util.HashMap;
7 import java.util.List;
8 import java.util.Map;
9 import util.DBConnection;
10
11 /**
12 *
13 * @author NevinYang
14 */
15 class Student { // 查询结果类，相当于一个JavaBean
16
17 private String Stu_id;
18 private String Stu_name;
19 private String Stu_sex;
20 private String Stu_grade;
21 private int Col_id;
22 private int Pro_id;
23
24 public String getStu_id() {
25 return Stu_id;
26 }
27
28 public void setStu_id(String Stu_id) {
29 this.Stu_id = Stu_id;
30 }
31
32 public String getStu_name() {
33 return Stu_name;
34 }
35
36 public void setStu_name(String Stu_name) {
37 this.Stu_name = Stu_name;
38 }
39
40 public String getStu_sex() {
41 return Stu_sex;
42 }
43
44 public void setStu_sex(String Stu_sex) {
45 this.Stu_sex = Stu_sex;
46 }
47
48 public String getStu_grade() {
49 return Stu_grade;
50 }
51
52 public void setStu_grade(String Stu_grade) {
53 this.Stu_grade = Stu_grade;
54 }
55
56 public int getCol_id() {
57 return Col_id;
58 }
59
60 public void setCol_id(int Col_id) {
61 this.Col_id = Col_id;
62 }
63
64 public int getPro_id() {
65 return Pro_id;
66 }
67
68 public void setPro_id(int Pro_id) {
69 this.Pro_id = Pro_id;
70 }
71
72 @Override
73 public String toString() {
74 return "Student{" + "Stu_id=" + Stu_id + ", Stu_name=" + Stu_name + ", Stu_sex=" + Stu_sex + ", Stu_grade=" + Stu_grade + ", Col_id=" + Col_id + ", Pro_id=" + Pro_id + ‘}‘;
75 }
76 }
77
78 interface Query { // 查询接口，有简单查询和缓存查询
79
80 public Student query(String sql);
81 }
82
83 class SimpleQuery implements Query { // 简单查询，相当于直接查询数据库，这里直接返回Result，相当于是数据库查询的结果
84
85 @Override
86 public Student query(String sql) {
87 Student student = new Student();
88 Connection conn = DBConnection.getConnection();
89 PreparedStatement pstmt = null;
90 ResultSet rs = null;
91 try {
92 pstmt = conn.prepareStatement(sql);
93 rs = pstmt.executeQuery();
94 if (rs.next()) {
95 student.setStu_id(rs.getString(1));
96 student.setStu_name(rs.getString(2));
97 student.setStu_sex(rs.getString(3));
98 student.setStu_grade(rs.getString(4));
99 student.setCol_id(rs.getInt(5));
100 student.setPro_id(rs.getInt(6));
101 }
102
103 } catch (SQLException e) {
104 System.out.println("操作中出现错误:" + e.getMessage());
105 } finally {
106 DBConnection.close(conn, pstmt, rs);
107 }
108 return student;
109 }
110 }
111
112 class CacheQuery implements Query { // 缓存查询，如果查询相同的sql，不直接查询数据库，而是返回map中存在的Result
113
114 private Query query;
115 private Map<String, Student> cache = new HashMap<>();
116
117 public CacheQuery(Query query) {
118 //此时这个query就为SimpQuery
119 this.query = query;
120 }
121
122 @Override
123 public Student query(String sql) {
124 if (cache.containsKey(sql)) {
125 return cache.get(sql);
126 }
127 Student student = query.query(sql);
128 System.out.println("执行了推入操作");
129 cache.put(sql, student);
130 return student;
131 }
132 }
133
134 class FilterQuery implements Query {
135 //过滤敏感词汇
136 private Query query;
137 private List<String> words = new ArrayList<>();
138
139 public FilterQuery(Query query) {
140 this.query = query;
141 words.add("杨晓龙");
142 words.add("杨晓亮");
143 }
144
145 @Override
146 public Student query(String sql) {
147 for (String word : words) {
148 if (sql.contains(word)) {
149 return null;
150 }
151 }
152 return query.query(sql);
153 }
154 }
155
156 public class Test {
157
158 public static void main(String args[]) {
159
160 Query simpleQuery = new SimpleQuery();
161 Student student1 = simpleQuery.query("SELECT * FROM student WHERE Stu_id=1");
162 Student student2 = simpleQuery.query("SELECT * FROM student WHERE Stu_id=2");
163 System.out.println(student1);
164 System.out.println(student2);
165 System.out.println(student1 == student2);
166 System.out.println("---------------------------------------");
167
168 Query cacheQuery = new CacheQuery(simpleQuery);
169 Student student3 = cacheQuery.query("SELECT * FROM student WHERE Stu_id=1");
170 Student student4 = cacheQuery.query("SELECT * FROM student WHERE Stu_id=1");
171 System.out.println(student3);
172 System.out.println(student4);
173 System.out.println(student3 == student4);
174 System.out.println("---------------------------------------");
175
176 Query filterQuery = new FilterQuery(simpleQuery);
177 Student filter1 = filterQuery.query("SELECT * FROM student WHERE Stu_name=‘杨晓龙‘"); // null
178 System.out.println(filter1);
179 Student filter2 = filterQuery.query("SELECT * FROM student WHERE Stu_name=‘杨晓亮‘"); // null
180 System.out.println(filter2);
181
182 }
183 }
对数据库的操作类：
1 import java.sql.Connection;
2 import java.sql.DriverManager;
3 import java.sql.PreparedStatement;
4 import java.sql.ResultSet;
5 import java.sql.SQLException;
6
7 /**
8 *
9 * @author NevinYang
10 */
11 public class DBConnection {
12
13 public static Connection getConnection() {
14 Connection conn = null;
15 try {
16 Class.forName("com.mysql.jdbc.Driver");//帮助建立连接
17 String username = "root";
18 String password = "123456";
19 String url = "jdbc:mysql://localhost:3306/student?"
20 + "useUnicode=true&characterEncoding=UTF-8";
21 conn = DriverManager.getConnection(url, username, password);
22 } catch (ClassNotFoundException e) {
23 System.out.println(e.getMessage());
24 } catch (SQLException e) {
25 System.out.println(e.getMessage());
26 }
27 return conn;
28 }
29
30 public static void close(Connection conn,
31 PreparedStatement pstmt, ResultSet rs) {
32 try {
33 //判断rs 等是否为空?
34 //如果为空会出现空指针异常
35 if (rs != null) {
36 rs.close();
37 }
38 if (pstmt != null) {
39 pstmt.close();
40 }
41 if (conn != null) {
42 conn.close();
43 }
44
45 } catch (Exception e) {
46 e.printStackTrace();
47 }
48 }
49 }
数据库创建语句：
create table student(
Stu_id varchar(32) NOT NULL,
Stu_name varchar(32) DEFAULT NULL,
Stu_sex varchar(32) DEFAULT NULL,
Stu_grade varchar(32) DEFAULT NULL,
Col_id int NOT NULL,
Pro_id int NOT NULL,
PRIMARY KEY (Stu_id)
) DEFAULT CHARSET=utf8
时间： 2024-10-07 06:55:12