自定义注解使用实例

 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 }

 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 }

 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 }

 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("zs@sina.com, li@163.com, ww@qq.com");//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 }