一、需求
1.有一张用户表，字段包括用户ID，用户名，昵称，年龄，性别，所在城市，邮箱和手机号；
2.方便的对每个字段的或字段的组合条件进行检索，并打印出sql语句。
二、代码
1.用户表的实体类
1 package com.anndemo.entity;
2
3 import com.anndemo.ann.Column;
4 import com.anndemo.ann.Table;
5
6 /**
7 * 用户表的实体类
8 * @author chen
9 *
10 */
11 @Table("user")
12 public class User {
13
14 @Column("id")
15 private int id;
16
17 @Column("user_name")
18 private String userName;
19
20 @Column("nick_name")
21 private String nickName;
22
23 @Column("age")
24 private int age;
25
26 @Column("city")
27 private String city;
28
29 @Column("email")
30 private String email;
31
32 @Column("mobile")
33 private String mobile;
34
35 public int getId() {
36 return id;
37 }
38 public void setId(int id) {
39 this.id = id;
40 }
41 public String getUserName() {
42 return userName;
43 }
44 public void setUserName(String userName) {
45 this.userName = userName;
46 }
47 public String getNickName() {
48 return nickName;
49 }
50 public void setNickName(String nickName) {
51 this.nickName = nickName;
52 }
53 public int getAge() {
54 return age;
55 }
56 public void setAge(int age) {
57 this.age = age;
58 }
59 public String getCity() {
60 return city;
61 }
62 public void setCity(String city) {
63 this.city = city;
64 }
65 public String getEmail() {
66 return email;
67 }
68 public void setEmail(String email) {
69 this.email = email;
70 }
71 public String getMobile() {
72 return mobile;
73 }
74 public void setMobile(String mobile) {
75 this.mobile = mobile;
76 }
77
78 }
User.java
2.表注解类
1 package com.anndemo.ann;
2
3 import java.lang.annotation.ElementType;
4 import java.lang.annotation.Retention;
5 import java.lang.annotation.RetentionPolicy;
6 import java.lang.annotation.Target;
7
8 /**
9 * 对应数据表的注解
10 * @author chen
11 *
12 */
13 @Target({ElementType.TYPE})
14 @Retention(RetentionPolicy.RUNTIME)
15 public @interface Table {
16
17 String value();
18
19 }
Table.java
3.字段注解类
1 package com.anndemo.ann;
2
3 import java.lang.annotation.ElementType;
4 import java.lang.annotation.Retention;
5 import java.lang.annotation.RetentionPolicy;
6 import java.lang.annotation.Target;
7
8 /**
9 * 对应数据表字段的注解
10 * @author chen
11 *
12 */
13 @Target({ElementType.FIELD})
14 @Retention(RetentionPolicy.RUNTIME)
15 public @interface Column {
16
17 String value();
18
19 }
Column.java
4.查询实现类
1 package com.anndemo.action;
2
3 import java.lang.reflect.Field;
4 import java.lang.reflect.Method;
5
6 import com.anndemo.ann.Column;
7 import com.anndemo.ann.Table;
8 import com.anndemo.entity.User;
9
10 /**
11 * 查询操作类
12 * @author chen
13 *
14 */
15 public class QueryAction {
16
17 public static void main(String[] args) {
18
19 User u1 = new User();
20 u1.setId(10);//查询id为10的用户
21
22 User u2 = new User();
23 u2.setUserName("Lucy");//模糊查询用户名为Lucy的用户
24
25 User u3 = new User();
26 u3.setEmail("[email protected], [email protected], [email protected]");//查询邮箱为其中任意一个的用户
27
28 String sql1 = query(u1);
29 String sql2 = query(u2);
30 String sql3 = query(u3);
31
32 System.out.println(sql1);
33 System.out.println(sql2);
34 System.out.println(sql3);
35
36 }
37
38 private static String query(User u) {
39
40 StringBuilder sb = new StringBuilder();//字符串变量(非线程安全)
41 //1.获取class
42 Class<?> c = u.getClass();
43 //2.获取到table的名字
44 boolean exists = c.isAnnotationPresent(Table.class);//检查User类中是否存在名称为Table的注解
45 if(!exists){
46 return null;
47 }
48 Table t = c.getAnnotation(Table.class);//获取Table注解
49 String tableName = t.value();//获取注解的属性值，即表名
50 sb.append("select * from ").append(tableName).append(" where 1 = 1");//拼装sql
51 //3.遍历所有字段
52 Field[] arrays = c.getDeclaredFields();//遍历User类中的所有属性
53 for(Field array: arrays){
54 //4.处理每个字段对应的sql
55 //4.1拿到字段名
56 boolean fExists = array.isAnnotationPresent(Column.class);//判断属性上是否存在名称为Column的注解
57 if(!fExists){
58 continue;
59 }
60 Column column = array.getAnnotation(Column.class);//获取Column注解
61 String columnValue = column.value();//获取注解的属性值，即表中的字段名
62 //4.2拿到字段值
63 String fieldName = array.getName();//获取属性名
64 String getMethodName = "get" + fieldName.substring(0, 1).toUpperCase() +
65 fieldName.substring(1);//获取该字段的getter方法名
66 Object fieldValue = null;
67 try {
68 Method getMethod = c.getMethod(getMethodName);//获取该字段的getter方法
69 fieldValue = (Object) getMethod.invoke(u);//通过反射获取getter方法的值
70 } catch (Exception e) {
71 e.printStackTrace();
72 }
73 //4.3拼装sql
74 if(fieldValue == null || (fieldValue instanceof Integer && (Integer)fieldValue == 0)){
75 continue;
76 }
77 sb.append(" and ").append(columnValue);
78 if(fieldValue instanceof String){
79 if(((String) fieldValue).contains(",")){
80 String []values = ((String) fieldValue).split(",");
81 sb.append(" in(");
82 for(String value: values){
83 sb.append("‘").append(value).append("‘,");
84 }
85 sb.deleteCharAt(sb.length() - 1);
86 sb.append(")");
87 }else{
88 sb.append(" = ‘").append(fieldValue).append("‘");
89 }
90 }else if(fieldValue instanceof Integer){
91 sb.append(" = ").append(fieldValue);
92 }
93 }
94 return sb.toString();
95
96 }
97
98 }
QueryAction.java
自定义注解基础知识参考：自定义注解(http://www.cnblogs.com/jinjiyese/p/4817645.html)
参考：慕课网(http://www.imooc.com/learn/456)
时间： 2024-07-28 18:42:31