java注解实例-反射生成sql

 定义描述用户表的注解：

package dao; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; 
// 做用域
@Target({ ElementType.TYPE }) @Retention(RetentionPolicy.RUNTIME) public @interface Table { String value(); }

 定义描述用户属性的注解：

 1 package dao;  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 
13 // 做用域
14 @Target({ ElementType.FIELD }) 15 @Retention(RetentionPolicy.RUNTIME) 16 public @interface Column { 17  String value(); 18 }

定义映射Bean类User：

 1 package dao;  2 
 3 /**
 4  *  5  * 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、手机号：  6  *  7  * @author 8  */
 9 @Table("user") 10 public class User { 11     @Column("id") 12     private int id; 13 
14     @Column("user_name") 15     private String userName; 16 
17     @Column("nick_name") 18     private String nickName; 19 
20     @Column("age") 21     private int age; 22 
23     @Column("city") 24     private String city; 25 
26     @Column("email") 27     private String email; 28 
29     @Column("mobile") 30     private String mobile; 31 
32     public int getId() { 33         return id; 34  } 35 
36     public void setId(int id) { 37         this.id = id; 38  } 39 
40     public String getUserName() { 41         return userName; 42  } 43 
44     public void setUserName(String userName) { 45         this.userName = userName; 46  } 47 
48     public String getNickName() { 49         return nickName; 50  } 51 
52     public void setNickName(String nickName) { 53         this.nickName = nickName; 54  } 55 
56     public int getAge() { 57         return age; 58  } 59 
60     public void setAge(int age) { 61         this.age = age; 62  } 63 
64     public String getCity() { 65         return city; 66  } 67 
68     public void setCity(String city) { 69         this.city = city; 70  } 71 
72     public String getEmail() { 73         return email; 74  } 75 
76     public void setEmail(String email) { 77         this.email = email; 78  } 79 
80     public String getMobile() { 81         return mobile; 82  } 83 
84     public void setMobile(String mobile) { 85         this.mobile = mobile; 86  } 87 }

根据参数动态返回查询语句：

 1 package dao;  2 
 3 import java.lang.reflect.Field;  4 import java.lang.reflect.Method;  5 
 6 /**
 7  * 根据参数动态返回查询语句  8  *  9  * @author10  */
11 public class ReturnQuery { 12 
13     public static String query(User u1) { 14         StringBuilder str = new StringBuilder(); 15         // 1.获取一个类class
16         Class c = u1.getClass(); 17         // 2.获取Table的名字
18         boolean exists = c.isAnnotationPresent(Table.class); 19         if (!exists) { 20             return null; 21  } 22         Table t = (Table) c.getAnnotation(Table.class); 23         String tableName = t.value(); 24         str.append("select * from ").append(tableName).append("where 1=1"); 25         // 3.遍历全部的 字段
26         Field fArray[] = c.getDeclaredFields(); 27         for (Field field : fArray) { 28             // 4.处理每一个字段对应的sql 29             // 4.1取到字段名
30             boolean fExists = field.isAnnotationPresent(Column.class);// 判断是否包含Column类型的注解
31             if (!fExists) { 32                 continue; 33  } 34             Column column = field.getAnnotation(Column.class); 35             String columnName = column.value(); 36             // 4.2取到字段的值
37             String fieldName = field.getName(); 38             // 获取相应字段的getXXX()方法
39             String getMethodName = "get" + fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1); 40             Object fieldValue=null; 41             try { 42                 Method getMethod = c.getMethod(getMethodName); 43                 fieldValue = getMethod.invoke(u1); 44             } catch (Exception e) { 45  e.printStackTrace(); 46  } 47             //4.3拼接Sql
48             if (fieldValue==null||fieldValue instanceof Integer &&(Integer)fieldValue==0) { 49                 continue; 50  } 51             str.append(" and ").append(fieldName); 52             if (fieldValue instanceof String) { 53                 if (((String) fieldValue).contains(",")) { 54                     String[] values=((String) fieldValue).split(","); 55                     str.append(" in ("); 56                     for (String s : values) { 57                         str.append("'").append(s).append("'").append(","); 58  } 59                     str.deleteCharAt(str.length()-1); 60                     str.append(")"); 61                 }else{ 62                     str.append("=").append("'").append(fieldValue).append("' "); 63  } 64             }else { 65                 str.append("=").append(fieldValue); 66  } 67  } 68         return str.toString(); 69  } 70 
71 }

测试类：

 1 package dao;  2 
 3 public class Test {  4     public static void main(String[] args) {  5         User u1 = new User();  6         u1.setId(10); // 查询id
 7 
 8         User u2 = new User();  9         u2.setUserName("JSFei"); // 模糊查询用户名
10         u2.setAge(21); 11 
12         User u3 = new User(); 13         u3.setEmail("123@163.com,123@qq.com"); // 查询邮箱有任意一个的用户
14         
15         String sql1 = ReturnQuery.query(u1); 16         String sql2 = ReturnQuery.query(u2); 17         String sql3 = ReturnQuery.query(u3); 18           
19  System.out.println(sql1); 20  System.out.println(sql2); 21  System.out.println(sql3); 22  } 23 }

输出结果：

...............................................