spring java配置方式@value注解取properties内容为null的一种情况

 1 package com.yangxin.springinaction.demo1;
 2 
 3 import com.alibaba.druid.pool.DruidDataSource;
 4 import org.springframework.beans.factory.annotation.Value;
 5 import org.springframework.context.annotation.*;
 6 import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
 7 import org.springframework.web.servlet.config.annotation.EnableWebMvc;
 8 
 9 import javax.sql.DataSource;
10 
11 
12 /**
13  * Created by Administrator on 2017/2/27.
14  */
15 @Configuration
16 @ComponentScan(excludeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION,value = {EnableWebMvc.class})})
17 @EnableAspectJAutoProxy
18 @PropertySource(value = "classpath:db.properties")
19 public class AppConfig {
20 
21 //    @Value("${jdbc.driver}")
22 //    private String driver;
23 //
24 //    @Value("${jdbc.url}")
25 //    private String url;
26 //
27 //    @Value("${jdbc.username}")
28 //    private String username;
29 //
30 //    @Value("${jdbc.password}")
31 //    private String password;
32     
33     //21 --- 31 行 这是取不到值得 作为方法入参可以取到
34 
35     @Bean
36     public DataSource druidDataSource(@Value("${jdbc.driver}") String driver,
37                                       @Value("${jdbc.url}") String url,
38                                       @Value("${jdbc.username}") String username,
39                                       @Value("${jdbc.password}") String password) {
40         DruidDataSource druidDataSource = new DruidDataSource();
41 
42         druidDataSource.setDbType("mysql");
43 
44         druidDataSource.setDriverClassName(driver);
45 
46         druidDataSource.setUrl(url);
47 
48         druidDataSource.setUsername(username);
49         druidDataSource.setPassword(password);
50 
51         druidDataSource.setMaxActive(10);
52         druidDataSource.setMinIdle(5);
53 
54         try {
55             druidDataSource.setFilters("stat, wall");
56         } catch (Exception e) {
57             e.printStackTrace();
58         }
59 
60         return druidDataSource;
61     }
62 
63     //这个bean不要忘记配置  如果不配置 上面取得的值为 @Value中的表达式 显然是不符合情况的
64     @Bean
65     public PropertySourcesPlaceholderConfigurer propertyConfigInDev() {
66         return new PropertySourcesPlaceholderConfigurer();
67     }
68 
69 }