深入JAVA注解之属性注解
项目目录结构
实体类：
1 package org.guangsoft.annotation.entity;
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 @Target(value = {ElementType.FIELD, ElementType.METHOD})
9 @Retention(RetentionPolicy.RUNTIME)
10 public @interface DBInfo {
11 //属性名参考com.mchange.v2.c3p0.DriverManagerDataSource
12 String driverClass() default "com.mysql.jdbc.Driver";
13 String jdbcUrl() default "jdbc:mysql://192.168.50.30:3306/guanghe";
14 String user() default "root";
15 String password() default "root";
16 }
DAO层：
1 package org.guangsoft.annotation.dao;
2
3 import org.guangsoft.annotation.entity.DBInfo;
4
5 import com.mchange.v2.c3p0.ComboPooledDataSource;
6
7 public class CommDAO {
8
9 @DBInfo
10 private ComboPooledDataSource dataSource;
11
12 public void setDataSource(ComboPooledDataSource dataSource) {
13 this.dataSource = dataSource;
14 }
15
16 public ComboPooledDataSource getDataSource() {
17 return dataSource;
18 }
19
20 }
service层：
1 package org.guangsoft.annotation.service;
2
3 import java.sql.Connection;
4
5 import javax.sql.DataSource;
6
7 import org.guangsoft.annotation.dao.CommDAO;
8 import org.guangsoft.annotation.utils.JDBCUtil3;
9
10 public class CommService {
11
12 public static void main(String args[]) throws Exception {
13 CommDAO commDAO = JDBCUtil3.createCommDAO();
14 DataSource dataSource = commDAO.getDataSource();
15 Connection connection = dataSource.getConnection();
16 System.out.println(connection);
17 }
18
19 }
util类：
1 package org.guangsoft.annotation.utils;
2
3 import java.beans.PropertyDescriptor;
4 import java.lang.reflect.Field;
5 import java.lang.reflect.Method;
6
7 import javax.sql.DataSource;
8
9 import org.guangsoft.annotation.dao.CommDAO;
10 import org.guangsoft.annotation.entity.DBInfo;
11
12 public class JDBCUtil3 {
13
14 //将注解注入到数据源类
15 private static DataSource getDataSourceByDBInfo (DBInfo dbInfo, DataSource dataSource) {
16 Method[] methods = DBInfo.class.getMethods();
17 for(Method method : methods) {
18 String name = method.getName();
19 try {
20 //注解类没有属性，反射注解类的方法名，内省出数据源类设置参数的方法, 找不到会抛异常，进入下次循环
21 PropertyDescriptor propertyDescriptor = new PropertyDescriptor(name, dataSource.getClass());
22 //注解类的方法能得到实际注解的值
23 Object value = method.invoke(dbInfo, null);
24 //用数据源的方法将注解类的值注入
25 propertyDescriptor.getWriteMethod().invoke(dataSource, value);
26 } catch(Exception e) {
27 continue;
28 }
29 }
30 return dataSource;
31 }
32
33 //工厂模式下的创建DAO
34 public static CommDAO createCommDAO() {
35 CommDAO commDAO = new CommDAO();
36 try {
37 Field[] fields = commDAO.getClass().getDeclaredFields();
38 if(fields != null) {
39 for(Field field : fields) {
40 field.setAccessible(true);
41 DBInfo dbInfo = field.getAnnotation(DBInfo.class);
42 if(dbInfo != null) {
43 //获取dao中dataSource的实体类ComboPooledDataSource
44 DataSource dataSource = (DataSource) field.getType().newInstance();
45 dataSource = getDataSourceByDBInfo(dbInfo, dataSource);
46 field.set(commDAO, dataSource);
47 }
48 }
49 }
50 }catch(Exception e) {
51 e.printStackTrace();
52 }
53 return commDAO;
54 }
55
56 }
结果（成功）：
